For a long while we have been told that humans mated with Neanderthals. Then we were told that humans mated with another type of ‘hominid’ called Denisovan. A recent article in New Scientist now tells us that a further type of hominid has now shown up in human DNA that has been labeled ‘Neandersovan’. These other hominds have all disappeared but small percentages of their DNA now shows up in the human genome. So I wrote to this guy who came up with this latest finding about Neandersovans. It was all becoming a bit too unbelievable for me – especially the fact that all these hominids have disappeared off the face of the Earth without any explanation.
My email to him:
I caught your article about the Neandersovans. I was wondering if you could help me with something. Lately there has been a spate of articles how humans mated with Neanderthals and Denisovans and now with hominids called Neandersovans.
Yet we are told that there is only a 1-2% difference in DNA sequence between human and chimpanzee.
So doesn't that mean that this DNA from all these hominids should be showing up in the DNA of the chimpanzee as well?
I can see how you might think that. It's confusing but true that modern Eurasians got about 2% of their DNA from Neanderthals, and also that humans differ from chimps at 1-2% of nucleotide sites. Yet this doesn't imply that we should find Neanderthal DNA in chimps.
The two percentages are not really comparable. It's true that perhaps 2% of my DNA came from a from Neanderthal ancestor. But at the vast majority of those Neanderthal-derived nucleotide sites, humans and Neanderthals are identical. Humans and Neanderthals are also identical at the vast majority of the nucleotide sites that I did *not* inherit from a Neanderthal. So humans are much more similar to Neanderthals than they are to chimps.
Humans have been separate from chimps about 10 times as long as they have been separate from Neanderthals. And even the shorter separation from Neanderthals was long enough to make interbreeding hard. It's unlikely that there could be interbreeding between humans and chimps.
My response to him:
“Humans and Neanderthals are also identical at the vast majority of the nucleotide sites that I did *not* inherit from a Neanderthal. So humans are much more similar to Neanderthals than they are to chimps.”
With respect I can't help feeling there's a flaw in your logic here cos the vast majority of sites that were not inherited from Neanderthal must have come from the common ancestor of human, Neanderthal and chimp. The orthodox view is that human and Pan branched off 6 million years ago so all the nucleotide sites we didn't inherit from Neanderthal must have come from the common ancestor that lived millions of years before that.
Modern humans are said to have migrated out of Africa about 2 million years ago and the conventional story is that humans mated with Neanderthals about 100K years ago and Denisovans about 50K.
We are told that there is 1-2% difference in DNA sequence between human and chimp, and as the chimp only inhabits parts of Africa, the only way this can be logically feasible is to assume that before the Neanderthals and other hominids and then the humans started to migrate from Africa the genomes of human, Neanderthal and chimp, and any other hominids as well, were identical.
A better story for the evolution of man doesn't require a missing link. A common ancestor simply evolved into humans, Neanderthals and other hominids, and chimps. You don't even need all that natural selection of adaptive phenotypes stuff. Especially as all of them at the molecular level are even more similar than sibling species. More like identical quadruplets.