First a special thanks to commenter race realist for his recent guest blogging on the evolution of human athleticism. Even though I don’t necessarily agree with every point, It was an incredibly well researched article that has stimulated a lot of great discussions.
An urgent request from Afrosapiens
Speaking of great guest bloggers, commenter Afrosapiens really wanted us to watch this urgent video he found on the internet:
Welcome to the real world, kids.
No donation is too small….
It’s an emergency, give guys please.I don’t know what to do to soften you hearts but please just do something, relay the message at least.
A DNA discussion
Well Afro was watching that urgent video, I was watching this presentation by Professor Moses Schanfield:
Now I’m no biologist (obviously) but I was struck by his claim around the 6 minute mark that only 2.5% of our DNA codes for phenotype. Now he notes that the other 97.5% of DNA is not truly junk DNA since it serves important functions, but one major function it serves is just to absorb harmful mutations. So if I understand correctly, animals were selected for a lot of non-coding DNA in part, to increase the odds that a mutation wouldn’t occur on the important genes? On the other hand, a lot of non-coding DNA can be very important in its own right, and is not just there to sacrifice itself for the coding DNA.
One of the arguments I’m always making is that how race, species (or other taxonomic categories) are classified by DNA, doesn’t perfectly correlate with how it’s classified by morphology. So one has to decide what one means by taxonomical categories like “race”, “species” and “genus”. Does one simply mean a group with a shared breeding history, or does one mean a group that is morphologically similar, or both? I prefer to define a taxon as:
A group of one or more populations of an organism or organisms that share a relatively similar phenotype genetically inherited from a common ancestor. The more shared the phenotype, the more specific the taxon (i.e. race is more specific than species which is more specific than genus).
So two populations might share a really recent common ancestor, but if they haven’t both preserved the phenotype of that common ancestor, they’re not in the same taxon as I would define it. Or, two populations might have identical phenotypes, but if they didn’t inherit them from the same common ancestor, they’re also not the same taxon, as I would define it.
On the other hand, two populations could share an incredibly ancient common ancestor, but if they both genetically PRESERVED the phenotype of that common ancestor, I’d consider them the same taxon no matter how old that common ancestor was.
That’s just my layman opinion, but even among specialists there’s great debate about how taxonomy should be done, so I don’ think the issue is settled.
One provocative part of the above video is at the very end: Schanfield seems skeptical of the widely accepted claim that modern humans interbred with Neanderthals. Neanderthals and modern humans are considered different species, and as Race Realist has pointed out, one definition of species is a population that can only produce fertile offspring with other members of its population. However I’ve heard on various reputable science documentaries (sorry no specific source) that primate populations that have been reproductively isolated for 1-2 million years can still produce fertile offspring so I don’t think that definition works.
Of course Schanfield is not arguing about the definition of species, but instead arguing that scientists can’t distinguish Neanderthal DNA caused by admixture from Neanderthals from DNA caused by ancient shared ancestry with Neanderthals.