“This suggests that when ancient humans met and mixed with Neanderthals, the two species were at the edge of biological incompatibility,” said Reich, who is also a senior associate member of the Broad Institute and an investigator at the Howard Hughes Medical Institute. Present-day human populations, which can be separated from one another by as much as 100,000 years (such as West Africans and Europeans), are fully compatible with no evidence of increased male infertility. In contrast, ancient human and Neanderthal populations apparently faced interbreeding challenges after 500,000 years of evolutionary separation.
“It is fascinating that these types of problems could arise over that short a time scale,” Reich said.
via Neanderthals’ Genetic Legacy | HMS.
An interesting article exploring the effects of Neanderthal DNA in the populations that have them (anyone whose heritage is outside of Africa).
I found the snippet above interesting. I’ve seen a lot of discussion recently in paleoanthropology about whether or not the various prehistoric populations of humanity should be considered separate species, or just variants of the same species. If us and Neanderthals were at the limit of compatibility, it seems to show that some of those other variants were probably not compatible.
My understanding of the definition of a species is that the individual members are genetically compatible enough for breeding. If Neanderthals, separated by a few hundred thousand years, were only borderline compatible, it probably indicates that Homo Erectus was probably not, and probably should be considered a separate species, at least in my completely inexpert opinion.
SelfAwarePatterns 
When seperating one species from another, there are actually two criteria: are they genetically dissimilar enough to prevent interbreeding OR are they geographically seperated so that interbreeding is unlikely to occur? For example, polar bears and grizzly bears are genetically compatible, but they live in such different environments that they rarely if ever get the chance to mate with each other, so they’re considered seperate species.
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Thanks. Interesting. I didn’t realize that. I would have thought they would have been sub-species, or something along those lines.
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The “species” concept is slippery! It actually provides a good way to explain why science is not-really about truth, or at least not a clear-cut idea of truth. But I’ll proceed in order…
The first part of my point is splendidly explained by Dawkins in his reply to the last Edge question:
http://www.edge.org/response-detail/25366
Essentialism is a wrong way of thinking because reality usually likes to mix things in ways that defy clearly cut categories. So, if you want to use the concept of “species” you can, but you should be very aware that the boundaries between species are both fuzzy and arbitrary. James’ example of polar/grizzly (and European brown) bears exemplifies the concept.
Dawkins however falls for the same mistake: by saying
he actually implies that “species” is a strong concept, an essence that we and our ancestors have in common.
The consequence of this observation (e.g. that the quoted sentence above isn’t really meaningful once we accept the fuzzyness of each single species and that there is no unique essence of any species) is somewhat surprising: should we stop talking about species altogether? I’d say no, we can still use the concept, but should accept that it is fuzzy and use it only when useful.
In practice I can still say “that’s a cat” and claim I’m saying something that’s true, but I should be aware that the truthfulness of such statement is strictly context-dependent. There are domains, for example if I was referring to the fossil of an ancestral “cat” (note the scare quotes), where it stops making sense.
That’s to say that the paleoanthropology discussion you’ve seen are actually equivalent of discussing the sexuality of angels. Discussing the interfecondity of different populations would make sense, but it can be done only if we’ll find genetic material to sequence. And even then, it’s slippery!
We now know that Euro/Asian current populations have some genes that came from Neanderthal ancestors, plus we know that Africans don’t. Crucially, we know it from the DNA that comes largely from a single Neanderthal individual. This means that it’s reasonable to expect that similar mixtures, and geographical segregations were affecting also the populations present at that time: but in this case, we are treating the DNA from a single toe as the “essential” description of a Neanderthal DNA. It is a questionable approach (still useful!), and a problem acknowledged at least by the authors of one of the studies (“The team has already begun trying to improve their human genome ancestry results by analyzing multiple Neanderthals instead of one”, see the link in the original post) but the main point remains: once you realise the limits of “essentialism”, your claims of truthfulness necessarily become fuzzy.
Doesn’t make science one single bit less useful, but it’s a humbling thought just the same…
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Thanks. I agree with everything you said, except I don’t think Dawkins fell for the mistake in his quote, but was using the common understanding of the word ‘species’ to make a point.
I knew that anthropological evidence for Neaderthal DNA was from a limited number of samples, but I didn’t realize it was one. Thanks for the info!
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Yes, it’s not clear if Dawkins is really doing that mistake or if he just settled for an easy-flowing sentence, accepting the (wrong) convention for clarity and simplicity. I decided to include my observation just the same because it exemplifies the slipperiness of the whole issue.
In the end, it has a lot to do with the fact (?!) that our brains are symbol-manipulation engines, use symbols as equivalence classes, and equivalence classes rely on essentialism. It’s a useful trick to be able to learn about the external world, but our comprehension has reached the point of exposing the limit of the whole approach. Whether we can truly think in other, non-essentialist ways is another matter though.
Anyway, thanks. I’ve been planning a blog post (or, as usual, a series of posts?) around these issues and thanks also to this short discussion I’m finally getting the needed clarity…
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