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dmehling

any examples of common ancestors?

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OK...

 

Let's go right back to the start. A) as the process of speciation is a population process and b) the categorization of species is effectively an arbitrary delineation on this continuous process; is it possible to consider "common ancestors" as "common ancestral populations"? The concepts and processes behind diversification are much easier to understand once we can discuss them as such.

 

Now, are we in agreeance that you are not part of the homogenous population that your grandfather was? This means you are not free to breed with the same individuals he was due to the temporal gap and generational turnover that occurs in humans. As an aside, humans are unusual in the biological world by having overlapping generations - so the effect of population differentiation on generational scales is usually more pronounced in other organisms.

 

Let's take it one more step backwards - the population, as defined above to which our great-great grandparents belonged to is no longer with us - in the sense that this population of humans is no longer contributing directly and significantly to the gene pool of the next generation. As such - it is not possible for the simultaneous existence of an interbreeding population of our great - great grandparents and a population of our own generation; thus it is not possible for a population of our ancestors and our own to be simultaneously extant.

 

Now if we go even further backwards - the common ancestral population which became - through the population level process of diversification over several generations humans and chimps, by the same logic as the impossibility of the co-existence of our great-great grandparents and our own generation - cannot be extant. Now the difference here is that most biologists are content to place the arbitrary delimitation of this common ancestral population as being representative of a species distinct from its deruvatives - the chimps and the humans.

 

As such, it is not possible for the common ancestor of two derivative species to be simultaneously extant as the derivatives. It's not reduction ad absurdum because we understand the process by which population differentiation occurs and based on this process we understand it to be not possible.

 

I'm not getting your point here... and I meant that the reduction ad absurdum was saying that chickens are fish (the delimitation of species is genetic, phenotypic, morphological, etc.)

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I'm not getting your point here...

 

The key points are :

 

1) It is not possible for a population of our ancestors (e.g. our great-great grandparents) and our own to be simultaneously extant.

 

2) Thus, it is not possible for the common ancestor of two derivative species to be simultaneously extant as the derivatives.

Edited by Arete

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The key points are :

 

1) It is not possible for a population of our ancestors (e.g. our great-great grandparents) and our own to be simultaneously extant.

 

2) Thus, it is not possible for the common ancestor of two derivative species to be simultaneously extant as the derivatives.

 

That would then be a petitio principi because I am contesting the point one one and thus the point two is not accepted either

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Ok, would you like to explain how a homogenous, interbreeding population of your great-great grandparents and a homogenous interbreeding population of your own generation can simultaneously exist?

I had thought I'd provided a relatively comprehensive explanation of why ancestral populations and contemporary populations do not co-exist and thus would not consider it to be begging the question to make an inference based on that presumption.

Edited by Arete

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Ok, would you like to explain how a homogenous, interbreeding population of your great-great grandparents and a homogenous interbreeding population of your own generation can simultaneously exist?

I had thought I'd provided a relatively comprehensive explanation of why ancestral populations and contemporary populations do not co-exist and thus would not consider it to be begging the question to make an inference based on that presumption.

It is a matter of lifetimes, sad thing I'm more informed about animals than about trees I cannot provide examples but I bet it is viable for an ancestral population that evolved into a different kind of plant to exist simultaneously... The ancestral population would survive through centuries in the same place while isolated descendants would evolve into something esle... When I mentioned my great great grandparents I refered to them as an example of dead beings that I am pretty sure belong to the same species as me... Furthermore, to the same taxa...

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If you can re-read post #25, it might become clearer - neither the in situ population, nor the divergent population ARE the ancestral population in your hypothetical. Both derive from it. The in situ population retains ancestral traits. This relates back to the example of the fish I posted in my initial response in post #3. The derivative populations display differing levels of phenotypic divergence from that ancestral state with some retaining a phenotype closer to the ancestral form than others, sure. This is rather unequivocal. None of them ARE the ancestral population which has long since expired.

 

Again, as I thought I'd explained at length in post #25, you and your grandfather do not belong to the same homogenous population. Your generation is derived from his. If part of your family moved to Madagascar and part stayed where you are now, you would not say your grandfather's population remained while another population went to Madagascar. Both the remaining population and the derived (Madagascan) population are derived from your grandfather's population. Again, as I explained in post #25, the arbitrary inference of a species boundary between two temporally disjunct populations is irrelevant to the process, which occurs at the population level.

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Also, bringing plants into this will further confuse the issue because they can do all sorts odd things when they hybridize or undergo polyploidy events. Even so, if the population is that long lived the time it takes to become sexually mature will probably be much longer than would allow for the populations to be able to evolve at the rate you are suggesting.

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If you can re-read post #25, it might become clearer - neither the in situ population, nor the divergent population ARE the ancestral population in your hypothetical. Both derive from it. The in situ population retains ancestral traits. This relates back to the example of the fish I posted in my initial response in post #3. The derivative populations display differing levels of phenotypic divergence from that ancestral state with some retaining a phenotype closer to the ancestral form than others, sure. This is rather unequivocal. None of them ARE the ancestral population which has long since expired.

 

Again, as I thought I'd explained at length in post #25, you and your grandfather do not belong to the same homogenous population. Your generation is derived from his. If part of your family moved to Madagascar and part stayed where you are now, you would not say your grandfather's population remained while another population went to Madagascar. Both the remaining population and the derived (Madagascan) population are derived from your grandfather's population. Again, as I explained in post #25, the arbitrary inference of a species boundary between two temporally disjunct populations is irrelevant to the process, which occurs at the population level.

 

But who is speaking about populations? I am speaking about taxa, taxa down to the smallest taxa; subspecies... Human subspecies do not exist but wolf subspecies do exist and my great grandparent may belong to a different generation and a different population (half of my great grandparents are Italian if not more than that, one is Scottish and I am Peruvian and mostly of Spanish ancestry but we are all human) but he belongs to the same species/taxa...

 

Also, bringing plants into this will further confuse the issue because they can do all sorts odd things when they hybridize or undergo polyploidy events. Even so, if the population is that long lived the time it takes to become sexually mature will probably be much longer than would allow for the populations to be able to evolve at the rate you are suggesting.

 

Well, yeah, plants can go through different processes but in that regards they still apply as more resistant to time... I did not know however that the more a plant can survive the later it reproduces, from an ecological collective perspective its logical but from a evolutionary individualistic perspective it makes no sense, however if scientific evidence corroborates their is an average constant proportion or some small range between life expectancy and reproductive maturity for plants I cannot argue otherwise but instead mention tardigrades and other extremophiles that have been known to lay dormant for many years and then, when the conditions allowed, get back to life, such creatures could survive to coexist with their evolutionary descendants...

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Well, yeah, plants can go through different processes but in that regards they still apply as more resistant to time... I did not know however that the more a plant can survive the later it reproduces, from an ecological collective perspective its logical but from a evolutionary individualistic perspective it makes no sense, however if scientific evidence corroborates their is an average constant proportion or some small range between life expectancy and reproductive maturity for plants I cannot argue otherwise but instead mention tardigrades and other extremophiles that have been known to lay dormant for many years and then, when the conditions allowed, get back to life, such creatures could survive to coexist with their evolutionary descendants...

 

There may or may not be a constant proportion between life span and sexual maturity, but there is definitely a link , and it also tends to correlate with amount of offspring. I don't see why it wouldn't make sense from and evolutionary survival perspective. If an organism has a long life it has a longer period of time that it can be taken advantage of by competitors so it should allocate a good amount of its energy to its own survival, a sort of support structure. Since the amount of energy allocated tends to be high and the energy needed to produce offspring is also high it cannot due both due to available energy restraints. This would put selective pressures on species to do one or the other but not both.

 

The tardigrades and other extremophiles that are dormant are completely different scenario. We have been looking at a set of populations of a species that have been breeding separately over time and comparing their descendants. When looking at the dormant extremophiles we may be directly comparing descendants to preserved ancestors instead, so it's not really a good comparison.

 

Also, since evolution only deals with populations and not individuals the discussion must be focused at the population level.

 

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But who is speaking about populations? I am speaking about taxa...

 

Diversification is a population process, which only makes sense in the context of populations. Species is an arbitrary and somewhat artifical system of categorizing a continuous process. I am repeating things I've already said:

 

Also, the process of biological diversification is a continuum, with the category of "species" being somewhat arbitrary.....So, in summary, the term "common ancestor" used in the literal sense, doesn't really take into account the continuous nature of evolution, the coalescent processes of speciation or the dynamic of stochastic drift. "Common ancestral population" may be a more appropriate way to phrase the term.

 

Even in the absence of divergence, if a contemporary population arises from an ancestral population, The ancestral population cannot simultaneously exist at the same time point as the derived population (unless you have a DeLorean I guess). If we consider contemporary species to be the same as their ancestors, chickens are really velociraptors, which are really amphibians, which are really fish, etc.

 

Let's go right back to the start. A) as the process of speciation is a population process and b) the categorization of species is effectively an arbitrary delineation on this continuous process; is it possible to consider "common ancestors" as "common ancestral populations"? The concepts and processes behind diversification are much easier to understand once we can discuss them as such.

Edited by Arete

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Diversification is a population process, which only makes sense in the context of populations. Species is an arbitrary and somewhat artifical system of categorizing a continuous process. I am repeating things I've already said:

 

 

Ok, now I understand you, well I don't think species is an artificial and meaningless classification, no do taxonomists and most evolutionary scientists nor do anyone that understands emergentism

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Ok, now I understand you, well I don't think species is an artificial and meaningless classification, no do taxonomists and most evolutionary scientists nor do anyone that understands emergentism

 

I am an evolutionary biologist who works on species delimitation and has published taxonomic revisions. I never said taxonomic classification was meaningless - I said it was arbitrary and I carefully stated that this was due to the process being continuous. The separation of organisms into a hierarchically classified taxonomic system is not due to the biological presence of systematically categorized biota - the diversification of biological organisms is a continuous, ongoing, dynamic process. the categories are there because it is easier for people, not because it is reflective of the processes from which biological entities diversify.

 

For this reason, thinking of common ancestors as taxa/species is less constructive than thinking of them in terms of populations. The process of diversification happens to populations rather than species - because species is a categorization we humans imposed on biological entities to assist our understanding of differences between populations of organisms rather than being representative of a hard boundary that actually exists in nature.

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I am an evolutionary biologist who works on species delimitation and has published taxonomic revisions. I never said taxonomic classification was meaningless - I said it was arbitrary and I carefully stated that this was due to the process being continuous. The separation of organisms into a hierarchically classified taxonomic system is not due to the biological presence of systematically categorized biota - the diversification of biological organisms is a continuous, ongoing, dynamic process. the categories are there because it is easier for people, not because it is reflective of the processes from which biological entities diversify.

 

For this reason, thinking of common ancestors as taxa/species is less constructive than thinking of them in terms of populations. The process of diversification happens to populations rather than species - because species is a categorization we humans imposed on biological entities to assist our understanding of differences between populations of organisms rather than being representative of a hard boundary that actually exists in nature.

 

Oh I see... then I was wrong to believe you knew a lot of the subject but that was not your specialty... You are licensed to be an authority in the matter yet accepting your word for that reason would be an ad verecundiam...

 

Is your position favoured by the scientific community or is your position one you are proposing to be incorporated?

 

Anyway, here I will tell you about many things you will consider mumbling if you do not read the whole text so please, read the following from the start to the finish;

 

Between lumper and splitters there is a lot of opposition in any field where categorization is necessary... I'm not graduated yet but I hope you dont take this to underestimate my words ro dismiss me as uninformed... That would be ad hominem and ad verecundiam fallacies and prejudice... However I admit you may have more scientific knowledge on the subject than me but I can provide you with a philosophical perspective (I am non-graduated student of philosophy, my knowledge is greater on ontology, philosophy of language, gnoseology and philosophy of biology than on any other field yet I prefer ethics and politics and may create a field of philosophy dedicated to narrative and categorization so the acknowledging of the lumper and splitter debate is important for me)...

 

In narrative we have clichés and similiar phenomenon that are called "tropes" by the best source of information about them I have ever found, the webpage "tv tropes". They too have lumpers and splitters that wanted to use less categories or split hairs... Wikipedia has an article for lumpers and splitters to (and wikieditors that want to lump every related article into one and wikieditors that want to split every article into more detailed articles)... Here is what wikipedia says on the subject:

 

A "lumper" is an individual who takes a gestalt view of a definition, and assigns examples broadly, assuming that differences are not as important as signature similarities. A "splitter" is an individual who takes precise definitions, and creates new categories to classify samples that differ in key ways.

 

Before that they present the same idea I am telling you;

 

Lumping and splitting refers to a well-known problem in any discipline which has to place individual examples into rigorously defined categories. The lumper/splitter problem occurs when there is the need to create classifications and assign examples to them, for example schools of literature, biological taxa and so on.

 

Wikipedia gives examples of the divide in the subjects of industry, biology, history, software modelling , language classification and liturgical studies but I can give further examples... Do you know the individualist and collectivist divide? Marxists are mostly collectivists (they champion equality at the cost of freedom), liberals are mostly individualists (they champion freedom at the cost of equality), neither get what they want (you cannot have freedom without equality and you cannot have equality without freedom)... Balance is necessary (ethics is very much shaped by the lumper/splitter or collectivist/individualist divide and I propose that neither position should we underestimated; altruism a lumper/collectivist position and egoism an individualist/splitter position, should be balanced according to my position; racism, classism, xenophobia, sexism and other such "me versus you" are other kind of intermediate position between lumping and splitting, they split humans by race/class/nationality/gender and lump individuals by the same categories, so you can see it is a double edged sword as you can do a negative balance of splitting and lumping, but you can go to the other extreme and lump everything as an animist would do and refuse to eat because any destruction is evil to you, then you would die from starvation as you can feed on air, and I have heard of a guy that actually died because he tried to eat nothing but air, it was in the news... in the opposite direction you can be an extremist splitter and follow Ayn Rand or, even worse, follow Ayn Rand with no concern for your future because "you are who you are now, you are not who you gonna be")...

 

This is just a long foreword to an accusation I have against you, but take it as positive criticism; you are splitting lifeforms too much when you split them into populations... It is next to impossible to work as a biologist or a scientist of any pertinent field with creatures on the population and generation level. Think how absurd would it sould if I splitted things even further and claim that since each individual is a snowflake with unique genes (or in the case of a snowflake, unique shape) I preteneded to claim that I can survive doses of water that would make any person of my age and weight and physical condition suffer water poisoning... Would it be logical if I did that and proceeded to experiment on it? Think of the problem of induction, it is a criticism against lumping things too much, i.e. it claims that lumping the past into the future as to assume that the laws of reality are permanent is a mistake, however we still do science that pretty much assumes that there is no such problem of induction... Why do we do so? Because we are pragmatic; We need to act and we need to act on educated guesses because we know we are always really betting and guessing but we realize that an educated guess has a better cost-benefit nature than a random guess. What do we use for educated guesses? Empirism and rationalism well balanced... What are classifications of categories for? They are a bet and the bet is that we can get results from lumping or splitting something to some degree between one and another point of lumping/splitting...

 

So sure, you can bet to divide creatures on the population level but think of the computing power it would demand on those studying life and its relationship to humans in the interest of the benefits of humanity? Lumping populations into species is much better according to a quick non-professional cost-benefit analysis and yet the lumping is not entirely arbiratry as you think, not more arbitrary than any use of language because emergence is a real phenomenon of nature... Rather than making myself the point on how lumping is not arbitrary I will refer you to the book that introduced me to the beauty of emergentism; "Gödel, Escher, Bach: An Eternal Golden Braid" by Douglas Hofstadter.

 

There it shows how while ants are thought to be individually instinctual they can show some degree of intelligence on the collective level... How sociology, anthropology and such sciences that study human collectivies study something that only exist in the plural that emerges from interaction of the singular, how reducing all sciences to physics just because physics center on the founding particles of existence is a mistake... Because things do have meaningful existence as collectivities... Even if they are not touching each other which you can argues is the truth about all reality, at the subatomic level we are all quarks not in contact with each other... But are we just that? Are we just quarks? Are we the machine Descartes thought animals were? My favourite field in science is anthropology (comparative mythology) and ethology and I hope I can study them both eventually so I can get better justification for lumping humanity as a species in the name of promoting secular humanism (many marxist, despite their collectivist nature, tend to oppose such lumping, they claim that what works for Europe does not works for Peru because we have different cultures, they lump philosophers by nationality more than they do by philosophical position, which I find stupid, I think that a British rationalist has more in common with a French rationalist than a German empirist with a German rationalist, likewise they oppose the lumping of people beyond the class criteria, because most of marxists are dirt poor or slightly more wealthy and resent the wealthier people, personally I am a social democrat and I believe in direct democracy and in the importance of simple living and investing everything one does not really needs in the benefit of one's society, so I have many points in commong with marxists, we are both left, but I'm not that bloodthirsty; as I learnt more about world mythologies I realized how human nature is so meaningful similiar between people, I love animals and that is why I love ethology but I would specialize in lumping anthropology on ancient humans with ethology on modern primates if I got to study those careers... Polymaths in the past like Leonardo Da Vinci lumped fields even less connected to each other so why would I not be able to if I succeed?). Empiric evidence shows that sentience is a meaningful classification, psychologists, ethologists and those researching the possibility of inventing artificial intelligence are not following a study of fictional elements... And the fact we have conscience and are exclusively physical has motivated the debate of dualists and monists that argued over splitting mind/matter or not, those that lumped mind and matter, monists, were further divided whether to accept mind (Descartes in some extent, Berkeley and other idealists) or to reject it and find everything to be material (Descartes in some extent, Marx and his many followers and Julien Offray de La Mettrie and other materialists)...

 

So think about species and see how meaningful it is, and by meaningful I mean "not exclusively arbitrary" or "not carelessly whimsical" or "useful for understanding, reaction and developing further knowledge and determining further action"...

 

I should quote wikipedia again;

 

The sorites paradox (from Greek:soureites, meaning "heaped up") is a paradox that arises from vague predicates. The paradox of the heap is an example of this paradox which arises when one considers a heap of sand, from which grains are individually removed. Is it still a heap when only one grain remains? If not, when did it change from a heap to a non-heap?

 

The word "sorites" derives from the Greek word for heap. The paradox is so named because of its original characterization, attributed to Eubulides of Miletus. The paradox goes as follows: consider a heap of sand from which grains are individually removed. One might construct the argument, using premises, as follows:

 

1000000 grains of sand is a heap of sand (Premise 1)

A heap of sand minus one grain is still a heap. (Premise 2)

Repeated applications of Premise 2 (each time starting with one fewer grains), eventually forces one to accept the conclusion that a heap may be composed of just one grain of sand (and consequently, if one grain of sand is still a heap, then removing that one grain of sand to leave no grains at all still leaves a heap of sand; indeed a negative number of grains must also form a heap).

 

Now wonder... Is not this solved by the premise that a heap of sand becomes such when a critical number of grains of sand are accumulated together as to hold them into the shape we have identified as a heap? Is not this meaningful and useful to determine the behaviour of a heap of sand versus the behaviour of scattered sand or oen grain of sand or sand in the beach in greater quantities than a heap? The same applies to the realism of intelligence and species... Are species arbitrary then? Not entirely because they are real... You know what is arbitrary? Calling a whale a fish, a bat a bird and an earthworm a snake, but before Linnaeus such classifications happened often (just read the bible or use the skeptic's annotated bible to find the lack of scientific rigor in the bible)... They are meaningless from a biological and genetic perspective but they are useful for an anthropological perspective and from an ecological perspective (If we had morphological categorization of animals we would know which niches relate better to which shapes, why the tasmanian devil looks so much like a canine, why not every aquatic mammal is as fish-like as whales and dolphins, I mean, just take a look at pinippeds, they are unique in shape, they dont look like amphibians or transitional species that life between water and earth, they have some common features but not all, this is what we can learn about ecology from inventing a morphological classification, for anthropology we can understand human interaction with animals and the role of animals by their niche and shape in human culture, the term "serpent" is already used in English for any creature, both real and mythical, that looks like a slender living cylinder, we can argue that dragons are a morphological-taxa above serpent because serpents can be dragons but dragons can be other than serpents)

 

The coastline paradox and the ship of Theseus, Heraclitus' maxim "you never bath twice in the same river because the apparent second time you do so neither you nor the river are the same" and even Zeno's paradoxes relate to the lumping and splitting divide... By splitting too much Heraclitus believed that tempus fugit, pantha rhei, carpe diem and you should not accept the "you versus other" dichotomy because even the idea of such a "you" being real is a mistake... By realizing that empirism favours splitting and rationalism favours lumping Zeno argued that empirism is an illusion and only the mind exists... Plato followed his teachings very closely... Thanks Aristotle came and set the studies in line for science to appear or we would be living with the technology of ancient greece or worse and believing in topos uranus and other useless heavens... Maybe under the golden dictatorship Plato wanted us to have in The Republic... If you wonder the coastline paradox is the paradox that the shape of a coastline is different at different degrees of analysis (i.e different scales) while the ship of Theseus is the question whether the ship is still the same after you replace one of its constitutent elements for an equivalent and so on until every element has been replaced; Is the ship the same if the elements are new? Likewise the problem of the philosophical zombie (whether a person can show sentience but actually lack it) is related to a variant of the ship of Theseus, known as Swampman;

 

Suppose Davidson goes hiking in the swamp and is struck and killed by a lightning bolt. At the same time, nearby in the swamp another lightning bolt spontaneously rearranges a bunch of molecules such that, entirely by coincidence, they take on exactly the same form that Davidson's body had at the moment of his untimely death. This being, whom Davidson terms 'Swampman', has, of course, a brain which is structurally identical to that which Davidson had, and will thus, presumably, behave exactly as Davidson would have. He will walk out of the swamp, return to Davidson's office at Berkeley, and write the same essays he would have written; he will interact like an amicable person with all of Davidson's friends and family, and so forth.

 

Donald Davidson, in his 1987 paper "Knowing One's Own Mind" wrote these words and then claimed "it can't recognize anything, because it never recognized anything in the first place." refering to the swampman as "it" instead of as "him" But I guess he did not read Hofstadter's book (that was published earlier in time, like 8 years or so I think)... You know Star Trek? I hope you do because I will take my example from an episode of The Next Generation and an episode of Deep Space Nine... You know they have "transporters", machines that do on purpose what coincidence did on Davidson's swampan thought experiment... William Thomas Riker, a character known in the older series as a commander and the right hand man of the captain of the spaceship where the adventure happens, was accidentally duplicated when he was still a lieutenant, the duplication meant that one of his two bodies lived for eight years stranded alone in a harsh planet and the other duplicate continued to ascend in ranks until he became the right hand man of a captain (and in future works a captain himself)... Which one is the real William Thomas Riker? At the time of the accident neither, and every second thereafter both were progressively growing into a newer character... One was known as William Riker and, for eight years, the other one was totally unknown so there was no one to give him a name and therefore he lost the right to the name William and instead became Thomas Riker... They further differentiated over time; William kept loyal to the federation and rised to captain, Thomas joined some rebels... Why do I give this solution to the swampman problem and the ship of Theseus? Because a person is not his body but his mind, even if his mind is just a codified organization of matter, this all has to do with the solution I give to the problem of lumping and splitting; critical mass. So this all relates to your splitting species to the population level... It can be a valid taxa (I advice you to propose populations as a subtaxa, below subspecies if you are so confident of their meaningful nature) but it is not a reason to disregard the value of species as a taxa (species are meaningful in genetics and biology and in ethology, what you learn about one horse applies equally well to a horse of a different population if you study them from the fields of genetics, biology or ethology)... For instance I favour the taxa of species but I acknowledge that the higher taxas are useful too (therefore I want to lump ethology and comparative mythology which I think is a form of anthropology that studies the instincts and primitive drives of humans; because I think I can learn about humans from studying animals and specially primates and other hominids)...

 

But the origina poster asked whether we have examples of common ancestors and even you agree we have them; dogs and modern wolves have ancient wolves as common ancestors...

 

 

 

 

 

 

In narrative we have clichés and similiar phenomenon that are called "tropes" by the best source of information about them I have ever found, the webpage "tv tropes". They too have lumpers and splitters that wanted to use less categories or split hairs... Wikipedia has an article for lumpers and splitters to (and wikieditors that want to lump every related article into one and wikieditors that want to split every article into more detailed articles)...

 

the line in paranthesis should read "and wikieditors that want to lump every related article into one and wikieditors that want to split every article into more detailed articles, they call them mergists and separatists"

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Oh I see... then I was wrong to believe you knew a lot of the subject but that was not your specialty... You are licensed to be an authority in the matter yet accepting your word for that reason would be an ad verecundiam...

 

Is your position favoured by the scientific community or is your position one you are proposing to be incorporated?

 

Anyway, here I will tell you about many things you will consider mumbling if you do not read the whole text so please, read the following from the start to the finish;

. . .

 

Nothing in your post does anything to invalidate the fact that classification of virtually any taxa, not just species, is fairly arbitrary while some are more arbitrary than others. Since we are talking about ancestral species it is even more arbitrary because there is no strict point at which one species becomes another. Even if there were we would have no way to show that two separate ancestral species were, in actuality, separate species. Something being arbitrary doesn't mean it's not real, it just means it there is not a strict way to delineate things so it is not an absolute category.

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Nothing in your post does anything to invalidate the fact that classification of virtually any taxa, not just species, is fairly arbitrary while some are more arbitrary than others. Since we are talking about ancestral species it is even more arbitrary because there is no strict point at which one species becomes another. Even if there were we would have no way to show that two separate ancestral species were, in actuality, separate species. Something being arbitrary doesn't mean it's not real, it just means it there is not a strict way to delineate things so it is not an absolute category.

 

I'm must disagree with you, arbitrary means it is decided by an arbiter, a referee, a judge... Someone that could do so out of mere whims... Arbitrary often implies that it indeed has been done out of pure whim... In this way what is arbitrary is rarely what is real... As by being arbitrary you can, on purpose, go against reality... For once I remember a guy that wanted to offend me so he arbitrarily claimed that everyone in my city and country lives in a straw house based on a photo he picked on the net despite it not being reality (where you life depends on how rich you are, poor people life in straw house but only the pporest of people, even the poor can sometimes afford brick houses)... I do not think that arbitrary oposes reality and I think nothing in reality is absolute... Everything is part of some continuum... by the way... I am confused... Ringer and Arete are different people? Aren't them? Because "ringer" can mean "postcript" in television if my memory serves right... and I was arguing with arete when a post came labeled "ringer" but then a guy or gal answered a question I needed solved and he or she used the name "ringer" and then again this time the answer is not a post after the post made by arete but after my post... I am confused...

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I'm must disagree with you, arbitrary means it is decided by an arbiter, a referee, a judge... Someone that could do so out of mere whims... Arbitrary often implies that it indeed has been done out of pure whim... In this way what is arbitrary is rarely what is real... As by being arbitrary you can, on purpose, go against reality... For once I remember a guy that wanted to offend me so he arbitrarily claimed that everyone in my city and country lives in a straw house based on a photo he picked on the net despite it not being reality (where you life depends on how rich you are, poor people life in straw house but only the pporest of people, even the poor can sometimes afford brick houses)... I do not think that arbitrary oposes reality and I think nothing in reality is absolute... Everything is part of some continuum... by the way... I am confused... Ringer and Arete are different people? Aren't them? Because "ringer" can mean "postcript" in television if my memory serves right... and I was arguing with arete when a post came labeled "ringer" but then a guy or gal answered a question I needed solved and he or she used the name "ringer" and then again this time the answer is not a post after the post made by arete but after my post... I am confused...

[emphasis added]

 

Just because you could doesn't mean you do. How does you example of a single person making a claim invalidate the fact that the boundaries of taxa are arbitrarily decided?

 

And yes I am a different person than Arete.

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[emphasis added]

 

Just because you could doesn't mean you do. How does you example of a single person making a claim invalidate the fact that the boundaries of taxa are arbitrarily decided?

 

And yes I am a different person than Arete.

 

Well, you are right but then the mistake is in the realms of communications; People learning to communicate better (from writers of any kind to public speakers an politicians) know that you use words based on their most common usage unless you want to exploit its flexibility in any way, either for fun or to twist the legal validity of the claim, that is why laws are worded with great effort and a very technical language in those places that do not use the common law... however, I must have you explain me what you say is any of my examples about "a single person making a claim", any claim, I need to understand what example you are refering to so I can explain (or better say, give deeper motivation) to how come it can or should invalidate what you call "the fact that the boundaries of taxa are arbitrarily decided"... So far I gotta say that the strongest realism has ever gotten has been when the concept of probability was deviced; rather than claiming that things are 100% real you assess a percentage bet on how real you think they are and you treat them as real if the chances are high... That is how modern science works (to circunvent the problem of induction) and how communication works (to understand a higher number of people)... That is why statistics is so meaningful; it does not give perfect resolution but it gives a proportionated solution... (For example, you trust condoms but we know that condoms are not 100% effective, but they are... good enough)

 

Edit: I find your description of my example to be too vague to be sure which example you are referign to or, better said, to make me remember what example I could have given that fits that description...

Edited by anotherfilthyape

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This is just a long foreword to an accusation I have against you, but take it as positive criticism; you are splitting lifeforms too much when you split them into populations... It is next to impossible to work as a biologist or a scientist of any pertinent field with creatures on the population and generation level.

 

Nature hasn't given you a choice. The process of biological diversification happens at the level of the population. If you wish to study the process of speciation, the toolkit necessary is that of population genetics. And prehaps a dozen journals are dedicated to it (Evolution, Molecular Ecology, Journal of Evolutionary Biology, Journal of Heredity, Molecular Phylogenetics and Evolution, etc). This and even my own research would indicate that far from being impossible, it is imperative to work on the scale of the population.

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Well, you are right but then the mistake is in the realms of communications; People learning to communicate better (from writers of any kind to public speakers an politicians) know that you use words based on their most common usage unless you want to exploit its flexibility in any way, either for fun or to twist the legal validity of the claim, that is why laws are worded with great effort and a very technical language in those places that do not use the common law... however, I must have you explain me what you say is any of my examples about "a single person making a claim", any claim, I need to understand what example you are refering to so I can explain (or better say, give deeper motivation) to how come it can or should invalidate what you call "the fact that the boundaries of taxa are arbitrarily decided"... So far I gotta say that the strongest realism has ever gotten has been when the concept of probability was deviced; rather than claiming that things are 100% real you assess a percentage bet on how real you think they are and you treat them as real if the chances are high... That is how modern science works (to circunvent the problem of induction) and how communication works (to understand a higher number of people)... That is why statistics is so meaningful; it does not give perfect resolution but it gives a proportionated solution... (For example, you trust condoms but we know that condoms are not 100% effective, but they are... good enough)

 

Edit: I find your description of my example to be too vague to be sure which example you are referign to or, better said, to make me remember what example I could have given that fits that description...

 

In scientific communication definitions are very strict so communication can be as unambiguous as possible. Your example was a personal communication, it is the same thing when people say evolution is only a theory. They refer to a common usage, not a scientific one. When I say the lines are arbitrary I mean that the boundaries are not strictly defined and so the boundary is a sort of best guess. To show taxa are not arbitrary you must show that the boundaries are strictly defined, not attempt to use an alternate definition of arbitrary.

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Nature hasn't given you a choice. The process of biological diversification happens at the level of the population. If you wish to study the process of speciation, the toolkit necessary is that of population genetics. And prehaps a dozen journals are dedicated to it (Evolution, Molecular Ecology, Journal of Evolutionary Biology, Journal of Heredity, Molecular Phylogenetics and Evolution, etc). This and even my own research would indicate that far from being impossible, it is imperative to work on the scale of the population.

 

Then should we not call the process speciation but populationization? Or something like that? Anyway, semantics aside... I have now to give my counterargument in the form of semi-rethorical questions; You see any merit in studying life forms by taxa (whether you study common properties among the same species or common properties among the same family or common properties among the same subspecies or common properties among the same order or so on? Do you see any value in that or do you hold that every study for animals must be done in the population level? So far it seems you only consider that population is what has to be analysed in the subject of speciation but you have left open the possibility that in other fields their is a use for higher taxa?

 

(by the way if populations are so pertinent they must be added to the taxonomic sistem as a taxa below subspecies, it must be data that common people can access too if they ever get interested to if we are to help humanity, I mean.. With the threats of obscurantism in the hands of religious zealots science and philosophy needs to be unified and more professionals should leave their desk and join the previous ranks of science popularizers and, furthermore, philosphy popularizers must arise too... Because only these fields of study; philosophy and science can save our future as... ¿a set of populations? although I guess that migration is so often in the human enviroment that you cannot treat cities as populations, you can? or you treat the whole of humanity as a single population? What do you do in regards to populations? how do the categorization of speciation by population behaves in relation to the mythology that we have races or to the more cultural than biological concept of ethnicities?)

 

How many populations can a species have? How do you delimitate a population to determine it is not the same population as another population? I mean, when you say "this species is not the same species as that" you have phenotypical divergences to prove they are different species (my favourite argument against the impossibility of Noah's ark is that you would demand that a man that confuses a bat with a bird determines that a moon bear and a sun bear and a spectacled bear are not the same despite having little differences that can be recognized only when you have accepted they are different species and it also applies to determining that a donkey and a horse are not the same species despite being so closely alike... sidenote; all the examples I know of hybridization between species of animals prove that sterility is the common ground between different species and the reason why hybridization is not considered a factor for evolution like mutation is so that is why I would learn a lot of you mentioned me any species that produce hybrids that have the same chances of sterility as purebreeds... however this could be more an argument against splitting two populations into different species than an argument against considering that there is any value for speciation in the concept of species but species also show phenotypic patterns common between individuasl we lump in the same species and a similiar make up in their DNA print) Now I want... What do you use to say that individual A is not of population alpha but of population B? as far as I know pulations can sometimes find meeting places... Cannot they? and how many populations would a species have thus how many populations would compose the world? I already use the argument against the Noah's Ark that species on the world are too many (and many more are unknown) to expect that a primitive fool could have identified a couple of each and that his ship was big enough to hold them all despite the little time he had to built it and collect them.

 

But I was sidetracking on other possible counterarguments... My interest to know is what solution you offer to ethologists and other people studying natural sciences like ecology or the relationship between humans and the animals they developed with throughout history or people studying any field of natural sciences where species or higher taxa are pertinent when they want to stablish a relationship between their field and the speciation process? Can people studying evolutionary psychology get far rather than obstaculized by the difficult of working with populations instead of species?

 

In scientific communication definitions are very strict so communication can be as unambiguous as possible. Your example was a personal communication, it is the same thing when people say evolution is only a theory. They refer to a common usage, not a scientific one. When I say the lines are arbitrary I mean that the boundaries are not strictly defined and so the boundary is a sort of best guess. To show taxa are not arbitrary you must show that the boundaries are strictly defined, not attempt to use an alternate definition of arbitrary.

 

You are right. I assumed however that "arbitrary" was not a technicism of scientists and thus it mean the same in the context of science as it meant in other contexts... What you say about scientific communication is also true about legal language and that kind of strict lack of "ambigousity" is something I which we could extend to every noun; only nouns; to have a scientific language to identify objects without ambigous nature, I mean, it is a problem when a word has one meaning in one dialect and another meaning in another dialect and a way more complex meaning on another language... It is what I wanted about morphology.... Anyway I will take your position now that arbitrary means "the boundary is a best guess";

 

Ok, the boundary is a best guess; Is not that true about everything about science? Everything about science is a best guess, you cannot be a good scientist without remembering two things 1.the problem of induction looms like the sword of Damocles over your head 2.Science is the field of analysing the past to make educated guesses to predict the future and prevent what you do not want and achieve what you do want and therefore it relies on being open to change the educated guesses as soon as it is proven necessary... Considering that, tell me; what is the meaningful difference between "best guess" and "educated guess"? Should we not consider species as valuable as populations? (Sidenote, Since we are now three people discussing these subjects and two of us have already manifested their academic background, what is your academic background Ringer? I want to know for mere curiosity)

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You are right. I assumed however that "arbitrary" was not a technicism of scientists and thus it mean the same in the context of science as it meant in other contexts... What you say about scientific communication is also true about legal language and that kind of strict lack of "ambigousity" is something I which we could extend to every noun; only nouns; to have a scientific language to identify objects without ambigous nature, I mean, it is a problem when a word has one meaning in one dialect and another meaning in another dialect and a way more complex meaning on another language... It is what I wanted about morphology.... Anyway I will take your position now that arbitrary means "the boundary is a best guess";

 

It's similar, but the law tends to leave quite a bit of room for interpretation in phrasing, even if they don't in words. In science leaving room for interpretation causes misunderstandings that are detrimental to communication.

 

Ok, the boundary is a best guess; Is not that true about everything about science? Everything about science is a best guess, you cannot be a good scientist without remembering two things 1.the problem of induction looms like the sword of Damocles over your head 2.Science is the field of analysing the past to make educated guesses to predict the future and prevent what you do not want and achieve what you do want and therefore it relies on being open to change the educated guesses as soon as it is proven necessary... Considering that, tell me; what is the meaningful difference between "best guess" and "educated guess"? Should we not consider species as valuable as populations? (Sidenote, Since we are now three people discussing these subjects and two of us have already manifested their academic background, what is your academic background Ringer? I want to know for mere curiosity)

 

To an extant yes everything in science is a best guess, but the terms themselves tend to be strictly defined in most sciences. If I talk about, say, oxidation of NADH the boundary of NADH/NAD in its oxidized and reduced form is easily defined. The problem is life tends to be a bit of a mess for easy definitions. Since biological systems are always changing and are always branching off of each other there isn't a good way to really say This is species A and this is species B unless they are very distantly related. The closer in relation they become they more fuzzy the boundary becomes. Not to say species is not a valuable concept, if it was not it wouldn't be used, but when talking about evolution it is necessary to look at populations. Even more so when ancestral species is brought into the discussion because it's virtually impossible to tell if the ancestral population could mate with the extant population even if their morphology seems to be exactly the same.

 

I'm not sure what it brings to the discussion but I am a student in biology and psychology, focusing on neurobiology.

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Do you see any value in that or do you hold that every study for animals must be done in the population level? So far it seems you only consider that population is what has to be analysed in the subject of speciation but you have left open the possibility that in other fields their is a use for higher taxa?

 

For someone so attuned to logical fallacy you've pulled a rather blatant strawman here. No one is claiming that the concept of species is flawed or useless. It's especially useful for a diversity of studies.

 

The original post asks a specific question about diversification - which is unequivocally a phenomenon which occurs amongst populations. Reciting the reasons why this occurs would be to simply recite the contents of your average first year evolution course. I've also already attempted to do the best I can via the medium of forum posts numerous times in this thread.

 

(by the way if populations are so pertinent they must be added to the taxonomic sistem as a taxa below subspecies, it must be data that common people can access too if they ever get interested to if we are to help humanity, I mean..

 

Evolutionary significant unit prehaps? http://en.wikipedia....ignificant_Unit

Genetic cluster? Clade? Flock/School/Herd/etc? Kin group? Race (ethnic, karyotypic, phenotypic) Colony? Any of the other categorizations used by the general public to define subsets of biological entities below the level of species used contiguously or otherwise by the general public or scientific community?

 

How many populations can a species have?

As defined earlier, a species can be defined as a metapopulation.

 

 

How do you delimitate a population to determine it is not the same population as another population?

 

Are you familiar with the term Panmixia? http://en.wikipedia.org/wiki/Panmixia. A population of sexually reproducing organisms can be defined as a panmicitic group of organisms. If the sampled group of organisms is not panmictic (as can be demonstrated with test of Hardy-Weinberg Equilibrium http://en.wikipedia....nberg_principle) it is comprised of more than one population.

 

all the examples I know of hybridization between species of animals prove that sterility is the common ground between different species and the reason why hybridization is not considered a factor for evolution like mutation is so that is why I would learn a lot of you mentioned me any species that produce hybrids that have the same chances of sterility as purebreeds

 

You have been provided with examples of how this assumption is false - hybridization occurs between species. Hybridization is a powerful force in evolution:

http://en.wikipedia....ki/Hybrid_swarm

http://www.ncbi.nlm....pubmed/21448227

http://rstb.royalsoc.../1506/2971.full

http://hydrodictyon....ization_Seminar

 

 

Here's a study which may be of particular interest:

http://bio.research....Hexagrammos.pdf

 

"Hybridization and introgression are antagonistic to the process of speciation. If hybrids are viable and backcross, introgression will slow or prevent the evolution of reproductive isolation between populations. If species hybridize upon secondary contact, introgression will ultimately erode species boundaries. If hybridization is rampant and gene flow is high, the proportion of hybrids will approach values expected with random mating, and introgression will overcome species boundaries, homogenizing populations. Alternatively, if species are genetically distinct, the proportion of hybrids would be significantly less than expected with random mating, gene flow would be interrupted by selection against hybrids, and inviability or sterility of F 1 hybrids or backcrosses would be expected. Here, we investigate a system with characteristics expected by both of these opposing scenarios. Hybridization occurs between three species of reef fishes in the genus Hexagrammos at unexpected high frequencies in a zone of distributional overlap. Backcrossed individuals are detected, indicating F1 hybrids are viable and capable of reproducing. Yet, these species are genetically distinct at multiple loci. To study this apparent paradox, we estimate the relative proportions of hybrids, patterns of symmetry, inviability, and cytonuclear disequilibria using one mitochondrial and two nuclear markers. We invoke selection against hybrids, at various life history stages, in the maintenance of species boundaries in this system."

 

 

And this one:

http://www.nature.co...ature03800.html

 

"Speciation in animals is almost always envisioned as the split of an existing lineage into an ancestral and a derived species. An alternative speciation route is homoploid hybrid speciation1 in which two ancestral taxa give rise to a third, derived, species by hybridization without a change in chromosome number. Although theoretically possible it has been regarded as rare1 and hence of little importance in animals. On the basis of molecular and chromosomal evidence, hybridization is the best explanation for the origin of a handful of extant diploid bisexual animal taxa2, 3, 4, 5, 6. Here we report the first case in which hybridization between two host-specific animals (tephritid fruitflies) is clearly associated with the shift to a new resource. Such a hybrid host shift presents an ecologically robust scenario for animal hybrid speciation because it offers a potential mechanism for reproductive isolation through differential adaptation to a new ecological niche7. The necessary conditions for this mechanism of speciation7 are common in parasitic animals, which represent much of animal diversity8. The frequency of homoploid hybrid speciation in animals may therefore be higher than previously assumed."

 

But I was sidetracking on other possible counterarguments... My interest to know is what solution you offer to ethologists and other people studying natural sciences like ecology or the relationship between humans and the animals they developed with throughout history or people studying any field of natural sciences where species or higher taxa are pertinent when they want to stablish a relationship between their field and the speciation process? Can people studying evolutionary psychology get far rather than obstaculized by the difficult of working with populations instead of species?

 

Understanding the role of the population in evolution is a fundamental building block one must understand in order to make any sense of the theory. To not understand the role of populations, gene flow and standing genetic variation and selection in the processes of evolution is to not understand evolution.

 

So my answer is, if one doesn't understand the importance of the population in the processes of evolution, one doe not understand the processes of evolution.

 

Ok, the boundary is a best guess.

 

No. groups of organisms exist in an infinite number of intermediate states between panmicitic populations and entirely diverged populations. There is no dichotomous set of two boxes into which all circumstances fit neatly, but infinite shades of grey between them. This leads to the boundary between taxonomic classifications being arbitrary.

 

As an analogy, if you had a paint store, you might divide your paints into colors. This is very useful for a broad range of applications, as someone who wants to buy a shade of blue paint can go to the blue section, someone looking for representatives of all the major shades can easily select representatives from each, etc and so on. HOWEVER, you probably have a vast number of colors which have elements of other colors. There may be a thousand shades between green and blue. A which point you stop putting the bluey-greens in the blue section and start putting the greeny-blues in the green section is going to be arbitrary and subject to a set of conditions predetermined by you. Even if someone else applies the same conditions, they might draw the line between blue and green at a different point to you.

 

The imprecision of species boundaries is not due to the process of defining them being "a best guess" or otherwise fundamentally inaccurate - the boundary is artificial in the sense that the things it delineates into neat clusters exist in a multitude of intermediate states between those classifications.

Edited by Arete

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So my answer is, if one doesn't understand the importance of the population in the processes of evolution, one doe not understand the processes of evolution.

 

Highly relevant bit.

Regarding species: as it has been explained numerous times by Arete and others, nature does not create strict boundaries. They are sometimes there, but then often times not. Just look at prokaryotes trying to find hard species boundaries is an exercise in futility. As such Arete is absolutely correct in saying that the delimiters are somewhat arbitrary. But, and that is the important bit, even if they do not reflect nature perfectly, they are useful. This is a basic thing that all biologists are aware of.

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It's similar, but the law tends to leave quite a bit of room for interpretation in phrasing, even if they don't in words. In science leaving room for interpretation causes misunderstandings that are detrimental to communication.

 

True... Thing is... I thought "arbitrary" was not a term with a specified meaning in science but that scientists used the same term as common people when they refered to "arbitrary"... Anyway, people that study the law develop less deeper studies in ontology, categoremas, categorization and language than taxonomists... I believe...

 

And When I said "I which we could extend to every noun; only nouns; to have a scientific language to identify objects without ambigous nature, I mean, it is a problem when a word has one meaning in one dialect and another meaning in another dialect and a way more complex meaning on another language... It is what I wanted about morphology..." I made a mistake... I meant "I wish" I dont know why I wrote the wrong word there...

 

To an extant yes everything in science is a best guess, but the terms themselves tend to be strictly defined in most sciences. If I talk about, say, oxidation of NADH the boundary of NADH/NAD in its oxidized and reduced form is easily defined. The problem is life tends to be a bit of a mess for easy definitions. Since biological systems are always changing and are always branching off of each other there isn't a good way to really say This is species A and this is species B unless they are very distantly related. The closer in relation they become they more fuzzy the boundary becomes. Not to say species is not a valuable concept, if it was not it wouldn't be used, but when talking about evolution it is necessary to look at populations. Even more so when ancestral species is brought into the discussion because it's virtually impossible to tell if the ancestral population could mate with the extant population even if their morphology seems to be exactly the same.

 

Easily defined? Every definition is hard, some are harder than others... Even the concept of categories is sometimes contested... Ontology is a hard field and scientists must realize that they have to know as much of ontology as ontologists must know about science.

 

I'm not sure what it brings to the discussion but I am a student in biology and psychology, focusing on neurobiology.

 

It brings to the discussion that you are somewhat more of an authority than me... I mean, yes, your studies do not mean you are necessarily right (believing so would be ad verecundiam) but it does gives credence to your words and it makes me realize you understand my claim that studies in the field of pscyhology cannot focus on single populations... I recommend you the book "Gödel, Escher, Bach: An Eternal Golden Braid", is a very good book...

 

For someone so attuned to logical fallacy you've pulled a rather blatant strawman here. No one is claiming that the concept of species is flawed or useless. It's especially useful for a diversity of studies.

 

The original post asks a specific question about diversification - which is unequivocally a phenomenon which occurs amongst populations. Reciting the reasons why this occurs would be to simply recite the contents of your average first year evolution course. I've also already attempted to do the best I can via the medium of forum posts numerous times in this thread.

 

Yes, sorry, I love biology and in school I was among the best students in biology but things changed when I went to university, we were forced to take a course of biology but the course was oriented toward the agendas of the teachers and did not helped me learn much beyond high school level, other than the concept of sustainability, everything I learnt about biology beyond high school I learnt it on my own through the net.

 

About the straw man, sorry for it, my bad, it was not intentional... I just had misunderstood your position...

 

Evolutionary significant unit prehaps? http://en.wikipedia....ignificant_Unit

Genetic cluster? Clade? Flock/School/Herd/etc? Kin group? Race (ethnic, karyotypic, phenotypic) Colony? Any of the other categorizations used by the general public to define subsets of biological entities below the level of species used contiguously or otherwise by the general public or scientific community?

 

Yes, but if you check any animal on wikipedia they list their taxas but not to which ESU they belong or which ESU they have.

 

As defined earlier, a species can be defined as a metapopulation.

 

Fine...

 

Are you familiar with the term Panmixia? http://en.wikipedia.org/wiki/Panmixia. A population of sexually reproducing organisms can be defined as a panmicitic group of organisms. If the sampled group of organisms is not panmictic (as can be demonstrated with test of Hardy-Weinberg Equilibrium http://en.wikipedia....nberg_principle) it is comprised of more than one population.

 

Ok... I guess humans are the most panmicitic of all species (I understand that panmixia is something where some evolutionary significant unit can have a higher degree of panmixia than another evolutionary significant unit)... I was not faimiliar with the term panmixia but I was familiar with the term "sympatric speciation" and "allopatric speciation"... With the degree of panmixia in humans and the way human "populations" are all sympatric... Would you say humanity can really be divided into populations?

 

You have been provided with examples of how this assumption is false - hybridization occurs between species. Hybridization is a powerful force in evolution:

http://en.wikipedia....ki/Hybrid_swarm

http://www.ncbi.nlm....pubmed/21448227

http://rstb.royalsoc.../1506/2971.full

http://hydrodictyon....ization_Seminar

 

 

Here's a study which may be of particular interest:

http://bio.research....Hexagrammos.pdf

 

"Hybridization and introgression are antagonistic to the process of speciation. If hybrids are viable and backcross, introgression will slow or prevent the evolution of reproductive isolation between populations. If species hybridize upon secondary contact, introgression will ultimately erode species boundaries. If hybridization is rampant and gene flow is high, the proportion of hybrids will approach values expected with random mating, and introgression will overcome species boundaries, homogenizing populations. Alternatively, if species are genetically distinct, the proportion of hybrids would be significantly less than expected with random mating, gene flow would be interrupted by selection against hybrids, and inviability or sterility of F 1 hybrids or backcrosses would be expected. Here, we investigate a system with characteristics expected by both of these opposing scenarios. Hybridization occurs between three species of reef fishes in the genus Hexagrammos at unexpected high frequencies in a zone of distributional overlap. Backcrossed individuals are detected, indicating F1 hybrids are viable and capable of reproducing. Yet, these species are genetically distinct at multiple loci. To study this apparent paradox, we estimate the relative proportions of hybrids, patterns of symmetry, inviability, and cytonuclear disequilibria using one mitochondrial and two nuclear markers. We invoke selection against hybrids, at various life history stages, in the maintenance of species boundaries in this system."

 

 

And this one:

http://www.nature.co...ature03800.html

 

"Speciation in animals is almost always envisioned as the split of an existing lineage into an ancestral and a derived species. An alternative speciation route is homoploid hybrid speciation1 in which two ancestral taxa give rise to a third, derived, species by hybridization without a change in chromosome number. Although theoretically possible it has been regarded as rare1 and hence of little importance in animals. On the basis of molecular and chromosomal evidence, hybridization is the best explanation for the origin of a handful of extant diploid bisexual animal taxa. Here we report the first case in which hybridization between two host-specific animals (tephritid fruitflies) is clearly associated with the shift to a new resource. Such a hybrid host shift presents an ecologically robust scenario for animal hybrid speciation because it offers a potential mechanism for reproductive isolation through differential adaptation to a new ecological niche. The necessary conditions for this mechanism of speciation7 are common in parasitic animals, which represent much of animal diversity. The frequency of homoploid hybrid speciation in animals may therefore be higher than previously assumed."

 

Of all the links you have provided so far the best one is the one of the hybrid swarm because it leads to an article on "Hybrid speciation" that mentions how the heliconius butterflies have generated hybrid swarms... But I love the subject of hybrids because chimeras have been my favourite kind of creature ever since I learnt about mythology and hybrids are the closest you can get to chimeras (I know that in science we get chimeras too but they are just not the same as hybrid, chimeras do not have hybrid vigour which mythical chimeras do have). This is why I have investigated everything I could about hybrids and I wanted to know anything about hybrids that could reproduce... The kind of evidence I wanted about it being possible was a list of species, evolutionary significant units or any other taxa that are known to hybridize benefiting from hybrid vigour and producing more unique creatures as a result... Ligers, the goat-sheep hybrids, hinnies, I find all such creatures interesting...

 

Understanding the role of the population in evolution is a fundamental building block one must understand in order to make any sense of the theory. To not understand the role of populations, gene flow and standing genetic variation and selection in the processes of evolution is to not understand evolution.

 

So my answer is, if one doesn't understand the importance of the population in the processes of evolution, one doe not understand the processes of evolution.

 

Ok, but even if you understand the processes of evolution you need to work with metapopulations, not with populations, it is too hard to make useful scientific advances when your studies are only pertinent to a single population

 

No. groups of organisms exist in an infinite number of intermediate states between panmicitic populations and entirely diverged populations. There is no dichotomous set of two boxes into which all circumstances fit neatly, but infinite shades of grey between them. This leads to the boundary between taxonomic classifications being arbitrary.

 

As an analogy, if you had a paint store, you might divide your paints into colors. This is very useful for a broad range of applications, as someone who wants to buy a shade of blue paint can go to the blue section, someone looking for representatives of all the major shades can easily select representatives from each, etc and so on. HOWEVER, you probably have a vast number of colors which have elements of other colors. There may be a thousand shades between green and blue. A which point you stop putting the bluey-greens in the blue section and start putting the greeny-blues in the green section is going to be arbitrary and subject to a set of conditions predetermined by you. Even if someone else applies the same conditions, they might draw the line between blue and green at a different point to you.

 

The imprecision of species boundaries is not due to the process of defining them being "a best guess" or otherwise fundamentally inaccurate - the boundary is artificial in the sense that the things it delineates into neat clusters exist in a multitude of intermediate states between those classifications.

 

Perfectly, your analogy is an excellent addition to this debate... And I have an explanation that serves as a solution;

 

http://en.wikipedia.org/wiki/Distinguishing_blue_from_green_in_language

http://en.wikipedia.org/wiki/Linguistic_relativity_and_the_color_naming_debate

http://en.wikipedia.org/wiki/Grue_and_bleen

http://en.wikipedia.org/wiki/Teal

http://en.wikipedia.org/wiki/Cyan

 

I guess you are familiar with this ontological problem and that is why you propose that the limits are arbitrary... It happens with other colours and with plant taxa too... (The expression orange and apples has been contested on linguistic grounds; http://en.wikipedia.org/wiki/Oranges_and_apples )... Etymologists are not sure what was called orange before, the fruit or the colour and we can say that the green of mucous is different than the green of the sea and the green of grass, that the blue seen in the sky, the blue in the sea, the blue in some birds are all different shades of blue... There are shades we might have hard time classifying but there are shades we can classify easily... We have a hard time distinguishing some individuals between close species but we have other individuals that are easily identified, or is that not the case?

 

http://en.wikipedia.org/wiki/Loki%27s_Wager

 

We cannot tell where the neck ends and the head begins but we can tell that the nose is in the head and Adam's apple is in the neck... The existence of gray is in no way a reason to deny the existence of black and white... It applies to morals too... The existence of things that are neither evil nor good does not means that good and evil do not exist... The solution to the colour problem is the following:

 

You can determine that violet or purple is the colour with a wavelength between 380 and 450 nm, that blue is the colour with a wavelength between 451 and 485 nanometers, that green has between 486 and 570 nanometers of wavelength, that yellow is 571 to 590, orange goes from 591 and 620 nanometers and red from 620 to 750 nanometers...

 

Human sight cannot diferentiate wavelengths of light so well as to make this differentiation useless... 415 nanometers of wavelength is deffinitely purple, 468 nanometers of wavelength is definitely blue, 528 nanometers of wavelength is definitely green and so on... Creatures do not have wavelengths... But they have genoma and dna... Now that the dna and genoma are getting broken and cracked we can find a way to determine limitations between species that is not as whimsical as saying "this is where green ends and blue begins" when a person that sells paints do it and which are of any use, the categories have been determined with more analysis and greater thought... By people with expertise in spectroscopy (you see I am using six colours instead of the traditional seven, but the traditional seven are an invention of Newton because he was still motivated by superstition, he can be the father of spectroscopy but he was just that, the father, not the specialist;

 

the ancient Greek sophists saw a connection between the colors, the musical notes, the known objects in the solar system, and the days of the week. but the human eye is relatively insensitive to indigo's frequencies, and some otherwise well-sighted people cannot distinguish indigo from blue and violet. For this reason some commentators, including Isaac Asimov, have suggested that indigo should not be regarded as a color in its own right but merely as a shade of blue or violet.)

 

Of course this is just an approximation, but we use an approximation for pi and that does not means that pi is arbitrary... Or is it?

 

However I still wonder how the fact that evolution happens on the population level means that an ancestor must be extinct for him or her to be considered an ancestor, I consider my father one of my ancestors and he is alive and he can have children, not with my mother but if they divorced or he cheated on her or she died he could impregnate a younger woman, his reproductive qualities are not extinguished but I still retain confidence in him being not only my father but my ancestor... The same applies to populations, species or evolutionary significant unit...

 

I must however admit one thing... Aren't we branching of into a debate that no longer relates to the OP's post? I mean, if you ask "are their any pair of evolutionary significant units that share a known common ancestors" the answer still is yes; any population of dogs and any population of contemporary wolves share the ancient wolves as ancestors... But back to the debate...

 

How can you delimitate populations for dogs? I mean, dogs are rarely ever mixed by breeds but breeds are found through all the world and they are controlled by human intervention so schnauzers only breed with schnauzers, fox terriers only breed with fox terriers and so on... But fox terriers and schnauzers are as much dog as each other is and both can live as close as neighbours and yet not interact with each other... The species problem is even more complex, or we can say, the population problem or the evolutionary significant unit problem, when human intervention is considered... A schnauzer from Lima, Peru has greater chances of interbreeding with a schnauzer from Pursat, Cambodia than schnauzer from Berlin, Germany has with a fox terrier from Berlin, Germany (yet mongrels exist, but how many mongrels exist is related to how many stray/street dogs exist, this is why I chose Berlin for comparision, I doubt they have many stray dogs or street dogs... I mean, the way their laws are so strict and correctly applied I guess they have avoided the problem of allowing dogs go stray... Mongrels and stray dog behave like the cities were another kind of natural enviroment, for us humans and our pets and the domesticated animals and not-so domesticated animals we manipulate cities and similiar anthropological units are artificial enviroments with human factor being stronger than natural factors; humans no longer adapt to the enviroment but adapt the enviroment to themselves and adapt themselves to each other, few adaptations are to the enviroment and these are mostly tools; clothing for colder or hotter climates, ointments to resist mosquitos and solar radiation, tools to reduce or eliminate plague-bearers, pathogens or other pests and problems, et cetera)

 

Bottomline, this is a linguistic and ontological problem not only a scientific problem. It may even involve mereology...

 

Highly relevant bit.

Regarding species: as it has been explained numerous times by Arete and others, nature does not create strict boundaries. They are sometimes there, but then often times not. Just look at prokaryotes trying to find hard species boundaries is an exercise in futility. As such Arete is absolutely correct in saying that the delimiters are somewhat arbitrary. But, and that is the important bit, even if they do not reflect nature perfectly, they are useful. This is a basic thing that all biologists are aware of.

 

I did not need Arete to tell me that nature lacks strict boundaries... I have been aware of that a long time already... Ontology and sociology and anthropology reveal the difficulty in determining boundaries, between language, culture, etc. I for once have been influenced by many cultures, from the British school I went to foreign television from Brazil, Venezuela, Colombia, Mexico, Japan, the United States and even the United Kingdom and some movies from China (such as the excelent The Gods Must Be Crazy III that mixes a bush tribe with the legend of hoping vampires and caucasian villians), Germany, Ireland, etc. Even tv series from Australia... My previous knowledge on physics and chemistry, while not extensive, was enough to understand the difficulty of boundaries, philosophy of time also helps to understand the difficulty in determining boundaries... When does the present starts an when it ends? When the past becomes the future? Where the sea ends and the land begins? Where a solid object ends and its fluid surroundings begin? Where matter ends and energy begins? Where one object ends and another object begins? Is there void gaps between space occupied by matter?

 

If you accept, in the field of mereology, that everything is composed of gunks, you understand that reality is filled with fuzzy bourders and has no strict bourders... This does not means that bourders are arbitrary because they are pragmatic... Bourders are not decided upon from a dogmatic position, not always, and when they are they often are useless, but bourders as decided by scientists are pragmatic... They are useful... We benefit from them...

 

http://en.wikipedia.org/wiki/Gunk_(mereology) Hope I'm not incomodating anyone with my persistence but I will persist until I run out of answers... or arguments... I feel debate benefits us...

 

 

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Yes, but if you check any animal on wikipedia they list their taxas but not to which ESU they belong or which ESU they have.

 

The population structure of all extant animals is unknown and different groups of humans use different terminology to describe variants below the level of species. Wikipedia is also not an authority on vertebrate diversity.

 

Ok... I guess humans are the most panmicitic of all species

 

As a concept, panmixia is a binary condition. Either all individuals in a given sample mate at random, or they don't. In reality, perfect panmixia doesn't exist, but using genetic tools we can evaluate significant deviations from the assumptions we make of panmictic populations.

 

Humans are not panmicitc at all and cluster genetically according to geographic region http://pritch.bsd.uc...nbergEtAl02.pdf

 

Sympatry refers to overlapping geographic distribution. If two populations occur in the same place, they are sympatric. Human populations in Asia are not sympatric with those in Europe. Migration occurs between these populations allowing for gene flow, but this is not the same as sympatry.

 

I was not faimiliar with the term panmixia but I was familiar with the term "sympatric speciation" and "allopatric speciation"... With the degree of panmixia in humans and the way human "populations" are all sympatric... Would you say humanity can really be divided into populations?

 

Human populations are not sympatric or panmicitic: http://pritch.bsd.uc...nbergEtAl02.pdf http://www.sciencedi...002929707605746

 

 

Of all the links you have provided so far the best one is the one of the hybrid swarm because it leads to an article on "Hybrid speciation" that mentions how the heliconius butterflies have generated hybrid swarms...

 

Glad you're coming around to understanding that hybridization can occur between species :) It is an interesting field.

 

Ok, but even if you understand the processes of evolution you need to work with metapopulations, not with populations, it is too hard to make useful scientific advances when your studies are only pertinent to a single population

 

One does not need to work on the level of meta-populations to conduct an evolutionary study. If the processes you are interested in happen at the population level that is the scale you work at. See population genetics, http://en.wikipedia....lation_genetics, phylogeography http://en.wikipedia..../Phylogeography landscape genetics http://webpages.icav...9/Papers/21.pdf etc.

 

However I still wonder how the fact that evolution happens on the population level means that an ancestor must be extinct for him or her to be considered an ancestor, I consider my father one of my ancestors and he is alive and he can have children, not with my mother but if they divorced or he cheated on her or she died he could impregnate a younger woman, his reproductive qualities are not extinguished but I still retain confidence in him being not only my father but my ancestor...

 

Generational overlap has already been discussed in this thread at length. in post #25, I tried to explain at length the separation of populations on the temporal scale.

 

I must however admit one thing... Aren't we branching of into a debate that no longer relates to the OP's post? I mean, if you ask "are their any pair of evolutionary significant units that share a known common ancestors" the answer still is yes; any population of dogs and any population of contemporary wolves share the ancient wolves as ancestors... But back to the debate...

 

That was not the question in the OP. The question was "Is there any examples where the common ancestor of two or more derived species is still extant?" [paraphrased]. As was explained at length, the ancestral population of two derived species cannot co-exist with it descendants. Hence the wolves/dog ancestor being ancient wolves and not contemporary wolves.

 

How can you delimitate populations for dogs?

 

Similarly to any other group of interest - examine genetic loci under netural selection for deviations from the assumptions of panmixia.

 

humans no longer adapt to the enviroment but adapt the enviroment to themselves and adapt themselves to each other, few adaptations are to the enviroment and these are mostly tools; clothing for colder or hotter climates, ointments to resist mosquitos and solar radiation, tools to reduce or eliminate plague-bearers, pathogens or other pests and problems, et cetera)

 

This is not true either. The "environment" in terms of natural selection, is any external factor which interacts with your genotype to influence your ability to pass genes on to the next generation. E.g. A child's genotype confers it a severe allergy to penicillin. It is prescribed penicillin, suffers a anaphylaxic reaction and dies. The deleterious components of its genotype were selected against by the environment. The ability to adapt the environment to better suit you does not eliminate selection by it - it simply changes the selection pressures.

Edited by Arete

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