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A question for Biologists.

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I have an issue on Natural Selection:

 

http://www.pnas.org/cgi/reprint/0508653103v1

 

The new study – published online in the Proceedings of the National Academy of Sciences – provides empirical support for the proposition that natural selection is a general force behind the formation of new species by analyzing the relationship between natural selection and the ability to interbreed in hundreds of different organisms – ranging from plants through insects, fish, frogs and birds – and finding that the overall link between them is positive.

 

 

The question is this (bolded in red). Comments much appreciated.

 

Look I explained you this a thousand times. Ask any biologist he'll agree. Natural selection hapens AFTER the apearance of a new specie. First you need to have an evolved specie, then it can overpopulate through natural selection. That makes natural selection a secundairy force in evolution, not a driving force. What they meant in this article is that natural selection does have an effect they had a lousy choice of words by saying it's a driving force. What they meant is that it can steer evolution to a certain direction. But natural selection does not cause new DNA. get your cause and effect right.

 

It's a forum debate, and I am simply asking what he suggested the answer will be if I ask any biologist, how accurate is this that is quoted above.

 

Many thanks

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its pretty accurate. natural selection cannot operate on a species unless it exists in the first place. this is not from a biological POV but simply a logical POV.

 

Natural selection is the process where bad genes will cause a disadvantage to the creature and because of this will die before passing the genes along.

 

it needs to have lived before it can die and natural seletion occur.

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We tend to see it as:

1) beneficial mutation occurs

2) natural selection acts to increase the proportion of that beneficial mutation within the population

 

Assuming that only one mutation is necessary to cause speciation and that mutation is beneficial to individuals who possess it, then yes, natural selection can only act on the individuals who already possess a mutation.

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he's wrong.

 

basically, random mutations create variability, and natural selection (broadly speaking) weeds out the crappy varients and promotes the spread of the good varients.

 

what he seems to be inplying is that mutation is the driving force behind evolution; however, mutation on it's own would not give evolution, it would just give variation and a degredation of genetic information over time... things would get less complex generation after generation, till they became unviable.

 

mutation + some kind of selection process = evolution. hence, natural selection is a driving force behind evolution.

 

"First you need to have an evolved specie, then it can overpopulate through natural selection. "

 

That is evolution. and it will create new species. by natural selection working on random variability.

 

Also:

 

"Proceedings of the National Academy of Sciences"

 

teehee, PNAS

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its pretty accurate. natural selection cannot operate on a species unless it exists in the first place. this is not from a biological POV but simply a logical POV.

 

if we're talking about the evolution of species, then dont forget that we'd be talking species1 --> species2.

 

natural selection is a driving force behind the evolution of species2 by acting upon species1.

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Not to be pulling teeth but ...

 

I think that saying something like speciation occurs when species1 --> species2 is inaccurate because it represents the idea of speciation as a linear progression.

 

In this particular PNAS article, I thought they were referring to allopatric speciation, where both populations diverge from each other so that over time, they are reproductively isolated from each other.

 

In other words, it's more like a V, with the original species at the bottom and the two daughter species at the top.

 

This is important because sometimes the daughter species are reproductively isolated from each other, but not from the "original species". For example, those lizard-thingys in California that make a species ring around the state.

 

Anyways, I don't think he's implying that mutation is the driving force behind evolution. I think he's just stating the obvious: you can't have natural selection unless variability already exists in the population. Variability is often caused by mutations in the genetic code.

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I have an issue on Natural Selection:

 

http://www.pnas.org/cgi/reprint/0508653103v1

 

The new study – published online in the Proceedings of the National Academy of Sciences – provides empirical support for the proposition that natural selection is a general force behind the formation of new species by analyzing the relationship between natural selection and the ability to interbreed in hundreds of different organisms – ranging from plants through insects' date=' fish, frogs and birds – and finding that the overall link between them is positive.

 

 

The question is this (bolded in red). Comments much appreciated.

 

 

 

It's a forum debate, and I am simply asking what he suggested the answer will be if I ask any biologist, how accurate is this that is quoted above.

 

Many thanks[/quote']

 

 

The problem comes with the term "specie". Natural selection needs an assembly of genes living together (let`s call it an individual!) to act on it. So one does not need a whole new specie to have natural selection, but simply an individual bearing a difference compared to his group (specie). If his difference provides it with an advantage or not will affect the natural selection.

 

So:

Specie is a term that we arbitrary apply to a heterous population that we put together due to great similarities. This is decided by humans so essentialy AFTER the facts of natural selection occured. Never forget that "natural selection" is applied to individuals (in real to genes, read Richard Dawkins that opened this depate looooong ago) and the term "specie" to a group of individuals. Therefore in such an explanation, it is clear that natural selection will occur before we decide that a group is a specie.

 

THOUGH, in your quote, this term is used clearly to identify individual(s) bearing a difference, which makes it 100% correct, but badly stated.

 

Hope it is clear?

 

Look at the exemple:

Bacteria A is a specie. Among this specie, one of the individuals gets a mutation that allows it to metabolise faster than others. Natural selection allows this individual to generate an increasingly important proportion of the descendants from this specie, hence generating a slightly different group of cells. If one can isolate an old A bacteria and the new mutated one, he would get somehow 2 different species. But only after the individual was favored is it possible.

 

Hope that it is clear. It is highly a question of semantic: Specie is arbitrary whereas natural selection is conceptual, so it is not obvious to mix them. Try and use individual instead of specie. It will actually renders your discussion more acurate as natural selection does not refer to species per se, but on interrelations between individuals, resources and other individuals.

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First, 'species' is both singular and plural, like 'sheep'.

 

Second, can occur in any population of organisms. If your species is one big population, then while they change over time due to natural selection, they're still just a different version of what came before.

 

However, if your species is one big population, but then is split into two smaller populations (say by rising sea levels), they're initially the same, but natural selection might take different directions in each of the now-separate populations. Over time, they become more and more different, until they can no longer interbreed, and thus are separate species.

 

So the short answer is that natural selection affects any population of animals. When it makes two populations increasingly different, that eventually results in speciation.

 

Mokele

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First' date=' 'species' is both singular and plural, like 'sheep'.

 

Second, can occur in any population of organisms. If your species is one big population, then while they change over time due to natural selection, they're still just a different version of what came before.

 

However, if your species is one big population, but then is split into two smaller populations (say by rising sea levels), they're initially the same, but natural selection might take different directions in each of the now-separate populations. Over time, they become more and more different, until they can no longer interbreed, and thus are separate species.

 

So the short answer is that natural selection affects any population of animals. When it makes two populations increasingly different, that eventually results in speciation.

 

Mokele[/quote']

 

 

Species:

 

Genus, species, sub-species (serovar and others)... So specie is a concise, precise, defined and arbitrary thing.

 

And Natural Selection is not acting on species, but on INDIVIDUALS (and even on genes to be more precise, again).

A new specie will come after a complete differentiation, but Natural Selection is already acting to promote the survival of ONE INDIVIDUAL before any descendant of this INDIVIDUAL is created. So NO, a SPECIE is not needed for natural selection if we are precise, simply because natural selection is acting on a lower level than that.

 

It is an old view that evolution is a question of species. Evolution is a question of fundamental units, simply: individuals; precisely: genes. Species are created once enough individuals are in it to form it. But how do these Individuals get an increasing proportion and survival? By natural selection.

 

We should think of evolution not only on mammals but also on bacterias. It makes it more precise.

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I think I'm having a little bit of trouble understanding the distinction being made. Immunologist, are you denying the existence of a gene pool, wherein members of a species more apt to survive under given conditions produce more offspring, thereby (over the course of many generations) diffusing a greater concentration of their genetic traits in the population as a whole, and "changing the species?"

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I think I'm having a little bit of trouble understanding the distinction being made. Immunologist, are you denying the existence of a gene pool, wherein members of a species more apt to survive under given conditions produce more offspring, thereby (over the course of many generations) diffusing a greater concentration of their genetic traits in the population as a whole, and "changing the species?"

 

No in fact I even prefer your way of saying it. What is important is the gene pool and the "new gene-bearer". The concept of its eventual offspring and the foundation of the gene pool will come after the initial survival of this new individual (and its replication). So natural selection is not acting on the gene pool itself, but on each gene-bearer in function of the concerned gene.

 

So the distinction being:

Species: Arbitrary decision of 2 different groups each containing heterogeneity in their respective gene pool.

 

Saying that natural selection occurs on new species is therefore impossible because it acts simply at the level of the individual (gene-bearer).

 

I am having a complicated issue here essentialy over a semantic question: a mutated individual and its first descendants do not form a different specie from their originating specie until they diverged enough. One gene difference is not enough to have a different specie.

 

Is it better?

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Hi Guys,

 

Thanks for your input so far.

 

I am wondering about the following scenario.

 

Is genetic recombination always a mutational process, with the recent example of the Galapagos finch rapidly evolving a smaller beak size then this evolutionary change could be said to have occured without a "smaller beaksize mutation" unless of course recombination changes are classed as "mutation"?

 

Thanks for all who have contributed.

 

Rapid Evolution of Darwins finches

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So specie is a concise, precise, defined and arbitrary thing

 

Actually, it *isn't* well-defined. Try finding a definition that *everyone* accepts and which works for all animals, sexual and non-sexual. You won't find one.

 

And Natural Selection is not acting on species, but on INDIVIDUALS (and even on genes to be more precise, again).

A new specie will come after a complete differentiation, but Natural Selection is already acting to promote the survival of ONE INDIVIDUAL before any descendant of this INDIVIDUAL is created. So NO, a SPECIE is not needed for natural selection if we are precise, simply because natural selection is acting on a lower level than that.

 

Natural selection affects the individual (not the gene; it's the individual who lives or dies), but individuals don't evolve, populations do. Populations (or gene pools) evolve based on which individuals natural selection kills or spares. So while the individual is what selection acts on, that action shapes the evolution of the population.

 

Also, there *is* species level selection, though granted it's not important as individual level selection. Imagine two species which are reproductively and geographically distinct, but fill the same niche. Now imagine that suddenly the geographic barrier has been removed, and the two species are competing for the same ecological niche. While natural selection is still acting on the individual, as always, in contrast to competition within a population, there are now two 'teams' (species) which do not exchange genes, rather than a free-for all where genes are mixed.

 

So the distinction being:

Species: Arbitrary decision of 2 different groups each containing heterogeneity in their respective gene pool.

 

What about asexual organisms? Each organism does not mix genes with any other, and thus there *is* no gene pool? This is what I mean about it being difficult to define a species.

 

Also, what of hybrids? Fertile inter-species hybrids are common, even between obviously distinct species. Hell, I've even seen an inter-generic hybrid (though I don't know if it was fertile).

 

Is genetic recombination always a mutational process, with the recent example of the Galapagos finch rapidly evolving a smaller beak size then this evolutionary change could be said to have occured without a "smaller beaksize mutation" unless of course recombination changes are classed as "mutation"?

 

Not strictly. Think of the genome like a deck of cards. Mutation changes the 3 of clubs into the 3 of hearts, recombination just shuffles the deck.

 

That said, recombination *can* occur within genes, altering their sequence and thereby causing mutation (like cutting the 3 of clubs and hearts in two, and taping them back together with the peices swapped). But recombination does not necessarily do that; it only happens in some cases.

 

Mokele

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What about asexual organisms? Each organism does not mix genes with any other, and thus there *is* no gene pool? This is what I mean about it being difficult to define a species.

 

Also, what of hybrids? Fertile inter-species hybrids are common, even between obviously distinct species. Hell, I've even seen an inter-generic hybrid (though I don't know if it was fertile).

 

Or how about prokaryotes? On the one hand they got asexual reproduction, on the other hand heavy horizontal gene transfer. Here we got, well, gene pools that flow into each other so to say...

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No true . NS is operative in the FORMATION of a new species by incremental steps . Each initial variation is subject to the forces of NS re its survivablity. A new species is generally definable by its inability to reproduce with its generative ancestral form or close relative . There are a few exceptions to this like mules , tigrons , etc

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It's a forum debate, and I am simply asking what he suggested the answer will be if I ask any biologist, how accurate is this that is quoted above.

 

Not at all accurate. THe part in red reflects a theory within evolution called the "neutral theory" of evolution. It was advanced by Kimura and colleagues and involved speciation.

 

There were two theories:

1. The original one proposed by Darwin -- where natural selection gradually transforms a population over generations such that the new population is so different from the original as to constitute a new species and be unable to interbreed with the original species. In this theory, reproductive isolation is a product of natural selection.

 

2. The neutral theory where reproductive isolation happens first to create a new species, then natural selection acts on it to change the new species.

 

The data is now very clear. #1 is correct can #2 is wrong. The PNAS paper is simply another nail in the coffin of #2. However, there had already been several studies in the lab and in the wild showing that it is natural selection that works on an isolated population of a species -- changing that population to meet the new environment. The result of those changes by natural selection is that the new population can no longer interbreed with the original population.

 

Sometimes natural selection works directly on genes that influence reproductive isolation. In fact, there is a study finding the genes that control hybrid sterility. When these genes are changed, the hybrids are no longer fertile among themselves or with the parent populations. And these are changed by natural selection.

 

References available upon request.

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Actually, it *isn't* well-defined. Try finding a definition that *everyone* accepts and which works for all animals, sexual and non-sexual. You won't find one. ... What about asexual organisms? Each organism does not mix genes with any other, and thus there *is* no gene pool? This is what I mean about it being difficult to define a species.

 

As you noted, it is impossible to provide an exact definition of species. That's because evolution is true. Since popuations transform gradually from one species to another, there is ALWAYS a gray area where it is unclear whether there is still one species or two.

 

Also, as you noted, the idea of species is different with different types of organisms. Mostly biologists use the biological species concept, which deals with the ability to interbreed.

 

But, for fossils, they use the morphological species concept which is based on differences in appearances.

 

For unicellular organisms, the genetic species concept is used. This looks at the genetic differences between populations.

 

Also, there *is* species level selection, though granted it's not important as individual level selection. Imagine two species which are reproductively and geographically distinct, but fill the same niche. Now imagine that suddenly the geographic barrier has been removed, and the two species are competing for the same ecological niche. While natural selection is still acting on the individual, as always, in contrast to competition within a population, there are now two 'teams' (species) which do not exchange genes, rather than a free-for all where genes are mixed.

 

You would get an argument here from most evolutionary biologists -- particularly Ernst Mayr (What Evolution Is). If you look, selection is STILL at the level of the individual. You still don't select for the group. It's just that one group has many more individuals that do well in the competition for scarce resources.

 

Think of the situation that the environment has changed -- now the envirionment includes competition for the same resources by individuals from the other species.

 

Also, what of hybrids? Fertile inter-species hybrids are common, even between obviously distinct species. Hell, I've even seen an inter-generic hybrid (though I don't know if it was fertile).

 

What this shows is that speciation is not a simple all-or-nothing event. There is a continuum of reproductive isolation during speciation, and in some cases fully separated species have not yet been formed.

 

This has also been studied in the lab. However, I would be interested in citations for your statement "fully fertile hybrids between obviously distinct species" Thank you.

 

Not strictly. Think of the genome like a deck of cards. Mutation changes the 3 of clubs into the 3 of hearts, recombination just shuffles the deck.[

 

That said, recombination *can* occur within genes, altering their sequence and thereby causing mutation (like cutting the 3 of clubs and hearts in two, and taping them back together with the peices swapped). But recombination does not necessarily do that; it only happens in some cases.

 

Not quite. Most traits are combinations of several genes. So a combination of alleles ABCD is a different trait than alleles abcd and AbCD or abCD, etc. Recombination shuffles alleles and can lead to the fixation of some alleles and elimination of others.

 

Thus, recombination could keep the combination of ABCD and AbCD. In that case, alleles a,c, and d are eliminated from the populationa and alleles A, C, and D are fixed.

 

So recombination can change the population by itself. In fact, recombination accounts for over 90% of variability within a population.

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2. The neutral theory where reproductive isolation happens first to create a new species, then natural selection acts on it to change the new species.

 

isn't neutral evolution stuff like random allele dropout in small populations, genetic drift, stuff like bottlenecking etc? i.e., prosesses that cause allele-frequency changes, but not in a manner that is affected by the fitness-of-survival benifit that the allele confurs to the possessing individual (or, i suppose, totally random 'evolution').

 

if not, what do those phenomena fit under?

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isn't neutral evolution stuff like random allele dropout in small populations' date=' genetic drift, stuff like bottlenecking etc? i.e., prosesses that cause allele-frequency changes, but not in a manner that is affected by the fitness-of-survival benifit that the allele confurs to the possessing individual (or, i suppose, totally random 'evolution').

 

if not, what do those phenomena fit under?[/quote']

 

It's both. :) It's confusing. You have the neutral theory of speciation, which is what the OP and I were talking about. And you also have the neutral (genetic) drift to allele fixation, which is what you are thinking of.

 

Bottlenecks are a different concept. If you have a bottleneck where the population drops to a low number, then fixation of traits by genetic (neutral) drift is more likely.

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ah right, i see. cheers :)

 

wasn't really sure if bottlenecks would count as neutral evolution, but couldn't think of any other examples off the top of my head.

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