Genetics question: Primate interbreeding

[briandunning]

I'm hoping someone knowledgeable can help me with some research. Mitochondrial DNA has shown that Homo neantherthalensis is NOT an ancestor of Homo sapiens. Is it known authoritatively whether they would have been able to interbreed, had they lived at the same time?

 

[RecoveringYuppy]

Don't think there's a definitive answer. The last study I saw found something like a .3% difference. Their conclusion was that we didn't interbreed and I don't recall that study expressing an opinion on whether they could.

ETA: This wikipedia article indicates there is no consensus and the hope is that the Neanderthal genome will be sequenced in a few years, hopefully settling the issue. It also cites a .5% difference rather that the .3 I recalled.

 

[Ichneumonwasp]

I don't think there is any way truly to know. Many have assumed that interbreeding was impossible because there is no evidence of Neanderthal mitochondrial DNA in humans today. The argument seems to run like this: humans and Neanderthals coexisted for long periods of time. Some humans will try to mate with anything that walks (let's hear it Dennis Hopper), within some reason. The absence of Neanderthal mitochondrial DNA would argue against our ability to produce viable offspring, since if we mated, there should be some evidence of it now.

I don't completely buy this argument for the following reasons:

1. We don't know how fertile Neanderthals were in the furst place compared with modern humans.
2. We don't know how fertile any offspring we might have had with Neanderthals would be.
3. It is entirely possible (though I think unlikely) that any human-Neanderthal offspring were killed off at some point when modern humans took over, just as the Neanderthal were killed off.

While it is very likely that Neanderthal and modern or other archaic humans could not produce viable offspring, I don't discount the possibility and don't see any way to prove it one way or the other.

 

[drkitten]

I don't think there is any way truly to know. Many have assumed that interbreeding was impossible because there is no evidence of Neanderthal mitochondrial DNA in humans today. The argument seems to run like this: humans and Neanderthals coexisted for long periods of time. Some humans will try to mate with anything that walks (let's hear it Dennis Hopper), within some reason. The absence of Neanderthal mitochondrial DNA would argue against our ability to produce viable offspring, since if we mated, there should be some evidence of it now.

Yup.

I don't completely buy this argument for the following reasons:

I find your reasons, ... unconvincing.

1. We don't know how fertile Neanderthals were in the furst place compared with modern humans.

If they were substantially less fertile than the rest of the Hominidae, they wouldn't have been as successful as they demonstrably were. Do you have any evidence suggesting that Neanderthals were less fertile than Saps?

2. We don't know how fertile any offspring we might have had with Neanderthals would be.

If the cross between a Neanderthal and a Sap is non-fertile, that means that Neanderthals and Saps cannot interbreed. Remember that mules are viable, but sterile. Biologists are comfortable with the idea that breeding that produces sterile offspring isn't "interbreeding."

3. It is entirely possible (though I think unlikely) that any human-Neanderthal offspring were killed off at some point when modern humans took over, just as the Neanderthal were killed off.

Yeah, it's also possile that they all flew away on great big silver space ships, and then only came back to pick up JFK and Elvis. By your own admission, this is an unlikely enough scenario that it can be discounted.

 

[RecoveringYuppy]

I don't think there is any way truly to know.

Well, "truly know" might be greater certainty than is reasonable to expect. If it turns out that our (Neanderthal and Sapiens) nuclear DNA is organized in to the same number of chromosomes and has differences comparable to what exist in our current genome I'd be convinced interbreeding was possible.

 

[Ichneumonwasp]

If they were substantially less fertile than the rest of the Hominidae, they wouldn't have been as successful as they demonstrably were. Do you have any evidence suggesting that Neanderthals were less fertile than Saps?

Not as such. I'm not arguing that they were less fertile, only that this is one of the problems in deciding whether or not viable offspring were possible.

With that said, the only evidence that I am aware of is that they tended to band together in smaller groups. Smaller groups have two obvious potential causes -- lower fertility rates and/or different social structure/interaction. There is no way to tell the difference at this remove, so it's all speculation. It was probably a social thing, though, based on the carrying capacity of the land and their particular diet.

If the cross between a Neanderthal and a Sap is non-fertile, that means that Neanderthals and Saps cannot interbreed. Remember that mules are viable, but sterile. Biologists are comfortable with the idea that breeding that produces sterile offspring isn't "interbreeding."

That is why I said less fertile, not infertile.

Yeah, it's also possile that they all flew away on great big silver space ships, and then only came back to pick up JFK and Elvis. By your own admission, this is an unlikely enough scenario that it can be discounted.

I'm not sure how unlikely it is as a scenario. I don't think it is very likely, but I wouldn't abolutely discount it. Again, those points were not to be taken as an argument for why I think it is likely that humans and Neanderthals could produce viable offspring. They were meant as potential confounders for anyone arguing that it is impossible for humans and Neanderthals ever to have mated successfully given the mitochondrial data. I think it might be possible. But I still think it is very, very unlikely that they could.

As evidence for the above claim (my uncertainty over the fate of any putative "hybrids"), there does seem to have been a bottleneck in human evolutionary history. We are thought to have been reduced to somewhere around 30,000 individuals at some point, were we not? It could possibly (however unlikely) be that any human-Neanderthal hybrids could have perished during that time period leaving behind no progeny.

By the way, JFK is not with Elvis. David Koresh is. They're in a time share in Pago-Pago.

 

[Ichneumonwasp]

Well, "truly know" might be greater certainty than is reasonable to expect. If it turns out that our (Neanderthal and Sapiens) nuclear DNA is organized in to the same number of chromosomes and has differences comparable to what exist in our current genome I'd be convinced interbreeding was possible.

Yep, but there are people out there who seem to be absolutely certain one way or the other. My point really is that we cannot be certain, so why argue about it?

 

[Madalch]

3. It is entirely possible (though I think unlikely) that any human-Neanderthal offspring were killed off at some point when modern humans took over, just as the Neanderthal were killed off.

It's entirely possible that such hybrids were considered very ugly by either neanderthal or human standards, and thus weren't very successful at reaching breeding age.

"This child is deformed." <toss>

 

[Soapy Sam]

While agreeing that we don't know, I lean towards the social differences argument to suggest it's unlikely.
Gorillas, Chimps, Bonobos and humans have very different social structures. Neanderthals , though closer to us than the other three, may also have had different social structure. If , for example, they tended more towards the alpha male with several females group structure of gorillas, it would have been very unlikely for crossbreeding to occur.
(Just because we are genetically close to Neanderthals need not imply cultural similarity. There have been human cultures with harems before now).

But speculation aside, I doubt we will ever have an answer to the OP, though if DNA recovery tecniques improve and we find a Neanderthal body in a tarpit, we might get lucky enough to define the degree of viability.