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Evolution Question

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Actually, the whole "interbreeding" thing is much more murky than one might suppose.

 

Yesterday I heard how two different species of frog interbred.

 

I though that 'species' are a definition of what can't interbreed?

 

There is no single definition of a species. It's a pretty fuzzy concept really.

Could the hybrid frog reproduce or was it sterile?

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How do you explain those people with ape-like faces and hair all over their bodies? Is this a gene from waaaay back when?? Or are their parents...??? You know? I own a book about freak shows. One of the people the book talked about was this girl who actually had the head of what looked like a chimp or an ape or something. It said that her whole family rejected her, hated her and treated her like less than human. Except....her mother!!! Now, idk but that's kinda fishy LOL. It's probably wrong, but it's funny to think about. I mean, WHY would she look like that? Then she had a baby, but it did die at birth and she died too. The baby was just as hairy with an ape head. So, technically, she couldn't give birth to a live child. Maybe it was interbreeding???

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But precisely this raises the question regarding the validity of such a kind of species concept.

 

Not really. Because evolution is true, any definition of species is going to have populations that are in the gray area of transforming from one species to another. Just get used to it.

 

It is quite clear that isolation of gene pools (either due to genetic incompatibility, spatial isolation or morphological incompatibility) is not clear cut enough to warrant a classification on which further (more universal) theories can be based on.

 

It's not clear cut precisely because those more universal theories -- evolution -- are true! Since species transform to new species gradually over hundreds/thousands of generations, at any given time there are going to be populations that are somewhere in that transition. If you have a speciation that takes 500 generations, you can't possibly point to generation 249 and say "we have species A) and then at generation 250 and say "now we have species B." But you can point to generation 1 as species A and generation 500 as species B. But no point in-between.

 

As I said before, species concepts of reproductive isolation do not work with prokaryotes (or for most non-sexually propagating organisms for that matter).

 

Of course. The biological species concept can only be used on contemporary sexually reproducing organisms. For non-sexually reproducing organisms you use the genetic species concept and for paleontology you use a morphological species concept.

 

Of course this is not directly related to the OP but is rather a general discussion on how species can be defined and whether such a distinction makes biological sense. The practical advantages are quite clear.

 

Yes, the distinction makes sense. The only biological reality is species. However, part of that "sense" is realizing that evolution makes precise definitions with no in-between examples impossible.

 

I though that 'species' are a definition of what can't interbreed?

 

The Biological Species Concept is more about populations that do not interbreed:

 

"Species are groups of actually or potentially interbreeding populations that are reproductively isolated from other such groups." (Mayr 1942)

 

That "reproductive isolation" can have several causes, and infertility is just one of them. Most of the barriers to reproduction are behavioral or physical, not genetic. In fact, a genetic barrier is the last in a line of isolating mechanisms. One of the most prevalent of isolating mechanisms is mate selection: one population simply does not perceive the other as being mates. This is the case with horses and zebras. They emphatically do not mate in the wild, even where their territories overlap. Yes, if you artificially insemminate, then you can get a hybrid. But in nature, such would never happen. You have 2 separate gene pools.

 

In terms of chimps and humans, neither species views the other as a potential mate. Now, whether the genetic difference over the speciations separating chimps and humans since the last common ancestor is enough to prevent a hybrid forming if we were to perform artificial insemmination was the question asked. But biologically, what is important is that chimps and humans, left to themselves, do not interbreed. Considering the number of speciations in both the chimp and human lineages, I would be surprised if you could get a viable hybrid.

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It's not clear cut precisely because those more universal theories -- evolution -- are true! Since species transform to new species gradually over hundreds/thousands of generations, at any given time there are going to be populations that are somewhere in that transition. If you have a speciation that takes 500 generations, you can't possibly point to generation 249 and say "we have species A) and then at generation 250 and say "now we have species B." But you can point to generation 1 as species A and generation 500 as species B. But no point in-between.

 

I think another way of saying this, is that all populations are "transition species" at all times. The process of evolution doesn't stop, even if a species experiences little evolution in a given time. Hardy-Weinberg equilibrium doesn't really exist in nature.

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The Biological Species Concept is more about populations that do not interbreed:

 

 

yes, there is a big difference between "can't interbreed" and "don't interbreed". Only the latter is meaningful in nature.

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Thank you, Paralith. It's interesting. What's a species, and what's not.

 

 

Hm. (When I start a thread about this, and the Tribal Masters deem it a Creationist thread to be destroyed at all costs... I'll just grin and think of Monty Python).

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Re chimp/human sex

 

Yes, of course it has been done, and many times.

The general rule in human sexuality is this : If you can imagine it, someone has done it!

 

I had a book some years ago that actually described a woman who kept a pet male chimp, who was specially trained to provide service. Guess what kind.

 

End result of all of this. There has never been a human/chimp hybrid born. It can't be done. Chimps and humans are too different genetically.

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I think another way of saying this, is that all populations are "transition species" at all times.

 

No, you can't say that. Because some species do go extinct and leave no ancestors. :) Also, species that are well-adapted to their ecological niche are under purifying selection: keeping them at that fitness and preventing change.

 

The process of evolution doesn't stop, even if a species experiences little evolution in a given time. Hardy-Weinberg equilibrium doesn't really exist in nature.

 

Yes, it does. In fact, most alleles at most times are at Hardy-Weinberg equilibrium. There are many studies showing Hardy-Weinberg equilibria:

 

"In most populations, the genotype frequencies at most loci fit the Hardy-Weinberg distribution very well. (We will illustrate this shortly.) ... The most important assumptions of the Hardy-Weinberg principle are: ...

2. The population is infinitely large (or so large that it can be treated as if it were infinite)" Futuyma, Evolutionary Biology, pg 237. 1999.

 

The population does not have to be "infinite" for Hardy-Weinberg to apply. Now to an example:

 

"From our hypothetical example, we have seen thatan array of genotype frequencies ... may or may not be in Hardy-Weinberg proportions of p^2:2pg:q^2. The principle's assumptions, such as infinite population size and no mutation, are manifestly unrealistic, so we might imagine that real populations would never fit its predictions. But as we noted above, the forces actiong on a real locus may be so weak, ormay balance each other in such a way, that reality may conform closely to the Hardy-Weinberg predictions. In fact, genotype frequencies in human and other populations very often fit Hardy-Weinberg proportions.

"Let us return to E.B. Ford's collection, made over 32 years, of Panaxia dominula. The sample consists of 17,062 A1A1, 1295 A1A2, and 28 A2A2 moths. We calculated p = 0.963 and q = 0.037. From our estimates of p and q, we can calculate the expected frequency p^2, 2pq, and q^2, thus the expected frequency of A1A1 is 0.963^2 = 0.9274. The expected numbers are calculated by multiplying the number of moths (N) by the expected frequencies, thus the expected numbre of A1A1 is 0.9273 x 18385 = 17,050. Continuing these calculations, we obtain the following results: [table] ...

"The difference between the observed numbers of each genotype and the theoretically expected numbers is so slight tht it can readily be attributed to accidents of sampling (SAMPLING ERROR). Thus, averaged over 32 years, this locus appears to be in Hardy-Weinberg equilibrium." Futuyma, Ibid, pg 237-238.

 

Sigh. I don't know how to put this tactfully, so I will apologize in advance for any offense I may cause. I do want to make a point: it seems that not only do creationists not read up on evolution, but that the vast majority of people supporting evolution do not either. I find so many myths about evolution propagated by supporters of evolution. iNow, you just demonstrated 2. Please invest in an evolutionary biology textbook and do some reading. At the least, accept the corrections from evolutionary biologists and cease making the false claims once you have been shown they are false.

 

Re chimp/human sex

 

Yes, of course it has been done, and many times. I had a book some years ago that actually described a woman who kept a pet male chimp, who was specially trained to provide service. Guess what kind.

 

Documented? Or urban legend? Your example may fit into the urban legend category.

 

The "many times" is not documented.

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To lucaspa

 

Re woman with chimp.

Of course it may be wrong. Anything we read in books may be wrong. However, with human/chimp interactions going back several hundred years (for westerners) anyone who believes that inter-species sex has not happened, and many times, is very naive. With sex, basically there is always someone who will do it.

 

I could tell some very lurid and fully documented cases of weird sex. Sometimes the utterly strange people involved will push the boundaries so far, it ends up killing them. Simply having sex with a chimp is almost normal by comparison.

 

We had a guy here in NZ who was into being abused by a dominatrix. He ended up being tied into a chair by said dominatrix and thrown over a waterfall - at his own insistence as detailed by a number of witnesses. It killed him. But apparently he got sexual jollies out of it. Go figure!

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I do want to make a point: it seems that not only do creationists not read up on evolution, but that the vast majority of people supporting evolution do not either. I find so many myths about evolution propagated by supporters of evolution. iNow, you just demonstrated 2. Please invest in an evolutionary biology textbook and do some reading. At the least, accept the corrections from evolutionary biologists and cease making the false claims once you have been shown they are false.

WTF are you talking about? I haven't even posted in this thread (at least, not until now).

 

Can you clarify the venom you've just spat in my direction, please, and advise precisely which comments I've made that imply I should "invest in an evolutionary biology textbook?"

 

Seriously, wtf?

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Further to what I was saying:

 

>> The Biological Species Concept is more about populations that do not interbreed:

 

Hmm.... so if human 'group' A (race, religion) refuse to interbreed with group B, that makes them a different species?

 

I think we don't know what a 'species' is.

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To vexer

 

If population A does not breed with population B, and enough time passes, we end up with 2 separate species. Do not forget the time factor - of the order of hundreds or thousands of generations.

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SkepticLance

 

Yes, but I am right: as long as A and B *can* breed, they are the same species.

 

(Actually, my earlier comment meant more than perhaps I'm permitted to say here)

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To vexer

 

Sadly, it is not as simple as that. Lots of occasions exist where two populations can interbreed, but are nevertheless considered different species. The definition of species is not really very clear cut.

 

This is especially true with certain microorganisms. Bacteria freely exchange genes, which is a kind of interbreeding, among widely differing species.

 

Lots of flowering plants can hybridise, but do not do so in nature, because of geographic or some other isolation, such as flowering times. They are considered to be separate species.

 

Even animals often have the ability to interbreed, but are nevertheless considered separate species. Cichlid fishes from the Lake Victoria region of Africa are known to evolve rapidly (100 years) into reproductively isolated groups that are visually distinctly different from each other. Many biologists consider those populations as separate species, in spite of strong genetic similarity.

 

There are butterflies which are genetically almost identical, but have different markings. Because of these visual differences, they do not interbreed in spite of being geneticaly able to. These groups are considered separate species.

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Further to what I was saying:

 

>> The Biological Species Concept is more about populations that do not interbreed:

 

Hmm.... so if human 'group' A (race, religion) refuse to interbreed with group B, that makes them a different species?

 

I think we don't know what a 'species' is.

 

That would technically be true (except for religion, because people of any race/group can convert). But I think you will find that due to our very long generation times, our ability to rapidly move throughout the globe, and that people of different races actually do mate with each other even when socially condemned, no such groups are likely to remain separate long enough to become genetically incompatible. Remember that species can merge, and that even a rather small amount of gene flow can prevent speciation.

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To lucaspa

 

Re woman with chimp.

Of course it may be wrong. Anything we read in books may be wrong.

 

What books?

 

However, with human/chimp interactions going back several hundred years[

 

What interactions? You have made the assertions but so far have offered no sources. I'm asking for the sources and you keep giving me more undocumented assertions.

 

I could tell some very lurid and fully documented cases of weird sex.

 

Then please provide us the sources for "fully documented cases" of human/chimp sex.

 

WTF are you talking about? I haven't even posted in this thread (at least, not until now).

 

My sincere apologies. I meant Ecoli. My mistake.

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My sincere apologies. I meant Ecoli. My mistake.

No worries. Thank you for having enough integrity to come back to that and respond. :)

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yes, there is a big difference between "can't interbreed" and "don't interbreed". Only the latter is meaningful in nature.

 

Well, that's not quite true. Species that can interbreed but don't (e.g via geographical isolation, or behaviour) tend to diverge intospecies tat cannot interbreed. The latter is usually a forerunner to the former.

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Well, that's not quite true. Species that can interbreed but don't (e.g via geographical isolation, or behaviour) tend to diverge intospecies tat cannot interbreed. The latter is usually a forerunner to the former.

 

Which is why the latter is so important. If a species does not interbreed, eventually the genetic distance will get to the point that they can't. By genetic drift if nothing else.

 

However, the point protist was making was that, in considering biological species, not interbreeding makes separate gene pools long before the genetic changes accumulate to "can't interbreed" (infertility). So, altho lions and tigers "can" interbreed in the sense that you can do artificial insemination to make ligers, lions and tigers are, in biological fact, separate species because they simply don't interbreed on their own. It is the "don't interbreed" that is critical biologically.

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This is something that's been bugging me for a long time.

 

Cattle were one of the first animals we domesticated. I believe they come Asia originally.

 

North American Bison have only recently been domesticated.

 

Bison and cattle can interbreed though. They will do so without artificial insemination. The resulting offspring are reproductively viable.

 

As species they diverged a very long time ago, and their populations were isolated at least since the Bering land bridge disappeared.

 

So how long does it take before divergent species can't interbreed anymore? Do we know? Does it differ in different species?

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Bison and cattle can interbreed though. They will do so without artificial insemination. The resulting offspring are reproductively viable.

 

As I read the data:

http://www.nature.org/wherewework/northamerica/states/southdakota/news/news2446.html

http://boldventure.info/dna.html

 

it appears that, altho artificial insemination is not used, artificial breeding conditions are used. IOW, a bison bull is presented only with cattle females in heat. Part of reproductive isolation is mate choice, and mate choice is not permitted.

 

For the wild herds, initial DNA testing does not show hybrids: "Tail hairs from 100 bison at Ordway Prairie were collected in the fall of 2006 and evaluated for cattle interbreeding in 2007. So far the results show only one animal has cattle genetics,"

 

That's not much. Also, it appears that not all hybrids are fertile. The second website takes pains to list each and every individual animal that is. That makes me think that this is unusual.

 

So I question the premise that bison and cattle are completely interfertile.

 

So how long does it take before divergent species can't interbreed anymore? Do we know? Does it differ in different species?

 

Probably differs from species to species. Although it may be fairly constant in terms of generations. May. Researchers are just starting to look at the molecular basis of speciation.

 

The gene involved in hybrid sterility has been identified at least in Drosophila and mammals have an homologous gene:

1. M Nei and J Zhang, Evolution: molecular origin of species. Science 282: 1428-1429, Nov. 20, 1998. Primary article is: CT Ting, SC Tsaur, ML We, and CE Wu, A rapidly evolving homeobox at the site of a hybrid sterility gene. Science 282: 1501-1504, Nov. 20, 1998.

 

The difference was 10-15 amino acids between sibling species.

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In-breeding and closely related species, like lions and tigers interbreeding, both these breeding scenarios produce some infertile offspring. What do both have in common that makes infertile offspring more likely?

Edited by dichotomy

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Thank you, lucaspa. That actually helps a fair bit. Even the part about the White Buffalo, which answers an unstated question about something so incredibly off-topic that some neo-mystics are likely to be a little pissed at me for a year or so.

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