What two mammalian species which most recently are known to have had a coommon ancestor are unable to produce hybrid offspring? I’m not concerned about whether the hybrid offspring are fertile or not, although that would be nice to know.
To clarify, I’m looking to see if, for instance, we know of two different species that seperated relatively recently and are unable to breed.
I ask this question as a way of making a guess at two questions that often come up on this board: 1. Could modern humans and Neanderthals interbreed? 2. Might it be possible for humans and chimps to interbreed?
Given that we think modern humans and Neanderthals shared a common ancestor about 500k years ago, I’m inclinded to believe that #1 was possible unless we know of two extant mammal species that split ~500k years ago and are unable to hybridize.
I’m guessing that it would be best to consider only large mammals with lifespans at least of the same order of magnitude (10) as humans.
What jumps up in my mind are dogs and foxes. I don’t know when they branched off the canine line though. I might even be wrong about the lack of viable hybreds, but I’ve never heard of it. I certianly run across wolf/dog and coyote/dog crosses often enough.
Zoogirl: Thanks for the reply. I know lots of species that can’t hybridize, but without knowing when they split off from eachother, it really doesn’t get to the question. Wolves and coyotes shared a common ancestor over 1M yrs ago, IIRC.
Referring to the list I do know that Coyotes and dogs can and will interbreed on their own (split @3mya)
Don’t know about the Black-Backed Jackals, but it seems likely since they share the same number of chromosomes as all of the wolf like canids see 2n column on Table 1. (which places them at about 7 mya - guess I’m going the wrong way, but how interesting, no?)
As for the OP and Neandertals (don’t know about chimps):
These guys are pretty sure that we did interbreed.
Of course you realize what the working definition (among several) of a species is:
An actually or potentially interbreeding population that does not interbreed with other such populations when there is opportunity to do so. - Ernst Mayr
Which means that most species won’t produce viable offspring (even sterile ones) due to a variety of Prezygotic (death before birth) and Postzygotic (death after birth) Isolation Mechanisms.
This is incorrect. “Prezygotic Isolation Mechanisms” does not mean “death before birth,” it simply means that no zygote (fertilized egg) is produced. These can include anything from behavioral mechanisms, such as courtship patterns, that usually prevent mating from taking place (in which case the species may be completely interfertile if mating does occur), to physiological conditions within the female’s reproductive tract that prevent sperm from reaching the egg, and a host of other mechanisms.
Dunno :). But I suspect that while a hybrid might be possible, the odds are good it would be sterile. The human lineage has undergone a Robertsonian fusion in chromosomes vis-a-vis the other great apes. So we have only 46 chromosomes to a chimps 48. See here:
The above probably aren’t absolute lines in the sand ( domestic and Prezwalski’s horses can produce fertile offspring despite chromosome counts of 64 and 66, respectively ), but they do tend to make it a little less likely.
Well there is the concept of instant speciation via chromosomal mutation that results in hybrid non-viability between the “parental” species/population and its mutant offspring. This may have happened with this little novelty ( which granted, is not a “large” mammal and is pretty darn unique ):
Robertsonian translocations in particular ( at least fusions, if not fissions ), like the one above, are apparently pretty common in mammals and a selection against heterozygotes might in theory lead to rapid, if not necessarily instantaneous speciation. But the concept has certainly been criticized ( see this article for some rebuttals and defense ):
I’m not really coming up with any large mammal species pairs that diverged recently and can’t produce fertile hybrids under lab conditions. But that might just be that I’m not looking hard enough. I’ll try poking around again later if nobody else comes up with anything :).
There is tremendous variability in the length of time two species have been separated before they lose the ability to produce hybrids. Chromosomal mechanisms have the potential to produce almost instantaneous inter-sterility, while some species have been separate for tens of millions of years and still can produce fertile offspring.
This article gives a review of chromosomal mechanisms of speciation.
While it is not the large mammal you are looking for, and while the actual time frame is not given, some populations of the House Mouse seem to have undergone chromosomal speciation in the very recent past:
Incidentally, I believe that the chromosomal difference between apes and humans is a Robertsonian rearrangement.
BTW, coincidentally I have NPR Science Friday on right now, and the interview is with Tim White and Svante Paabo (Im sure you’re familiar with these two guys). One topic is Sapiens/Neanderthal DNA mixing.
FTR, Robertsonian translocations are pretty common in humans. A person who has Robertsonian translocation of chromsome 21 will always produce triploid 21 (Down Syndrome) children (the other option is monoploid 21 which is inviable), except in the extremely rare case of nondisjunction of 21 in the other parent. This will lead to whole chromosome uniparental disomy of 21, which may have no phenotype:
Humans and chimps differ by 1.24% of their DNA. That is ridiculously little. We can all hazard a guess if chimps and humans could produce a hybrid: I bet that they could, with a bit of chromosomal gymnastics at mitosis. The hybrids probably wouldn’t be fertile – the pericentric inversions would mean that pairing in meiosis would be enormously disrupted. In fact, we use a similar technique in the fruit fly to prevent recombination at all, but I think there would be serious issues with nonrecombined chromsomes and later genomic imprinting (along with the bizarre meiotic figures mentioned by Colibri).
I know you were talking about mammals, but I am currently working on a group of different species of flies that are around 5-10% genomically diverged from each other (under 6 million years of evolutionary divergence). Many of them can produce interspecific hybrids, and some can even produce fertile interspecific hybrids. The male genitals of these species seem to be among the most highly divergent phenotypic characteristics, and production of the hybrids seems to depend a lot on how compatible the genitals are. So, in some sense, one could claim that the chihuahua and Great Dane do not produce hybrids (even though they are of the same species) because of genital incompatibility. One could speculate that if a population of chihuahuas and a population of Great Danes became feral (and survived and thrived), they would not interbreed and would presumably soon speciate. So simple genetic differences may not be the only reason behind production of hybrids.
As far as I’m aware, this is not the case with humans and chimps. But I profess deep ignorance of these matters.
Ouch, well now we’re getting just a bit picky. :rolleyes:
But of course you are right…
I just didn’t find the need to explain this any further - the OP was probably not concerned with the details of Isolation Methods (of which I can bore the best of 'em with - if you’d like, from now on I will elaborate)
“Interspecies chimeras are made in the laboratory. There have been rat/mouse chimeras and recently a rabbit/human mix (it was not allowed to develop beyond a few days).”
