Are There Two (or more) Living Species of Humans?

For those of you looking for some racist rant, you’re not going to find it here, despite the interesting title.

Here’s the conjecture; there’s a lot of genetic diversity in humans. Is there enough variation between humans to prevent two of them from producing fertile offspring, and if so, could they be considered two different species of humans?

Amongst the seven species in the genus Equus, we know that horses and donkeys can breed together, but always create sterile offspring (mules, that is). Likewise, zebras and donkeys have produced the “zeedonk”, which is also sterile. The definition of a species separation is that two animals from separate species cannot produce fertile offspring. Sterile mules and zeedonks, fine, but you won’t be seeing a purebred line of mules any time soon.

So theory has it that speciation occurs when two groups from one species are separated for so long that accumulated mutations in their DNA prevent them from making babies effectively, or making effective babies. It’s actually senseless to speak of two species that can crossbreed, because then, of course, by definition they are the same species.

But here is where it gets interesting. Let’s break a species up into tribes, or herds, whatever. What if tribe A can breed with tribe B, and tribe B can breed with tribe C, and C with D, and D with E. But they are spread across the country, and though there’s been some local mixing, tribe A is so genetically different from E that they can’t breed at all. Are they then different species? If a meteor came along and wiped out B, C, and D, then there would be no doubt at all that A and E were now different species. And yet, if you plopped all these tribes into a city, you would only have a statistic for “infertility” between certain members that appeared to be unable to produce fertile kids; the Zeedonks of the human species, the chance meeting of a type A and type E person.

So it’s entirely conceivable that all humans could mate with 99% of all other humans, but would qualify as a “different species” when paired up with any member of the other 1%. Thus, though the species superficially looks like a single species, you could selectively sample two humans and technically prove they are different species, even though each of them could produce viable offspring with a large and overlapping majority of other humans. Wouldn’t that be odd?

It would be interesting and informative to take a broad sampling of genes from both parents of sterile children and see if, statistically, they have a much broader genetic difference than parents of non-sterile kids. It would also be telling to know if children from mixed marriages (racial, not religious!) tend to have a higher incident of sterile offspring. And lastly, if any of this is correct at all, I would expect that the percentage of sterile offspring would be on the rise, because the world has lost its tribal nature and interracial marriages are much more common than they used to be. This should be a fairly easy statistic to locate and correlate with the evolution of travel in the world, with isolationist communities like China offering a valuable “control experiment”.

A problem with this list of data-mining “experiments” is that our society tends to associate sterility with an individual, not with his or her parents. We need to establish a data-base of genetic information that goes back a generation from the sterile individual, not assume that the cause of the problem started with him.

Of greater significance and concern is that our rush toward universal mixing, though perhaps ethically desirable, could result in such an incredible diversity of genetic mixing due to the huge population involved that the norm might become sterility. There may be a maximum population-mixing size allowable before it self-sterilizes, and forces itself into a mass speciation event. Or it could mean the opposite, and human blending will become so complete that there could never be a human Zeedonk. It’s hard to say; the rules of human society have had such a non-natural effect on the rules of evolution that they hardly apply to us anymore, despite the fact that we continue to mutate and evolve, or devolve as medical advances help keep us alive. However, I find the questions that I’ve proposed of weighty enough substance that, hopefully, someone with more intelligence and energy than myself may decide to pursue them to their natural solutions.


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