Thursday, May 06, 2010

50 million Neandertals living today

Or 50 million Neandertal equivalents ....
NEANDERTALS LIVE! | john (Neandertal) hawks weblog
... In genetic terms, we can ask, how many times has the average Neandertal-derived gene been replicated in our present gene pool? Those aren't Neandertal individuals -- that is, a forensic anthropologist wouldn't classify them as Neandertals. They're the genetic equivalent.
The answer to this is also simple: In absolute terms, the Neandertals are here around us, yawping from the rooftops.
There are more than five billion people living outside of Africa today. If they are one percent Neandertal, that's the genetic equivalent of fifty million Neandertals walking the Earth around us.
Does that sound minor? If I told you that your average gene would be replicated into fifty million copies in the future, would you be satisfied? Maybe your ambition is greater, but I think the Neandertals have done very well for themselves.
Does this mean that Neandertals belong in our species, Homo sapiens?
Interbreeding with fertile offspring in nature. That's the biological species concept.
Dogs look a lot more diverse than modern humans and neandertal humans, and they interbreed happily. We are one with Neandertal. Tell the BBC, Walking with Cavemen needs an epilogue.

Hawks has written a long, excited, essay with the occasional sentence fragments. He's probably been hitting the champagne. Today's Nature articles on the Neandertal genome are a validation of his research and his enthusiasms.

There's more (emphases mine).
... Burbano and colleagues put together a microarray including all the amino acid changes inferred to have happened on the human lineage. They used this to genotype the Neandertal DNA, and show that out of more than 10,000 amino acid changes that happened in human evolution, only 88 of them are shared by humans today but not present in the Neandertals.
That's amazingly few.
Green and colleagues did a similar exercise, except they went looking for "selective sweeps" in the ancestors of today's' humans. ... They identify 212 regions that seem to be new selected genes present in humans and not in Neandertals. This number is probably fairly close to the real number of selected changes in the ancestry of modern humans, because it includes non-coding changes that might have been selected.
Again, that's really a small number. We have roughly 200,000-300,000 years for these to have occurred on the human lineage -- after the inferred population divergence with Neandertals, but early enough that one of these selected genes could reach fixation in the expanding and dispersing human population. That makes roughly one selected substitution per 1000 years.
Which is more or less the rate that we infer by comparing humans and chimpanzees. What this means is simple: The origin of modern humans was nothing special, in adaptive terms. To the extent that we can see adaptive genetic changes, they happened at the basic long-term rate that they happened during the rest of our evolution.
Now from my perspective, this means something even more interesting. In our earlier work, we inferred a recent acceleration of human evolution from living human populations. That is a measure of the number of new selected mutations that have arisen very recently, within the last 40,000 years. And most of those happened within the past 10,000 years.
In that short time period, more than a couple thousand selected changes arose in the different human populations we surveyed. We demonstrated that this was a genuine acceleration, because it is much higher than the rate that could have occurred across human evolution, from the human-chimpanzee ancestor.
What we now know is that this is a genuine acceleration compared to the evolution of modern humans, within the last couple hundred thousand years.
Our recent evolution, after the dispersal of human populations across the world, was much faster than the evolution of Late Pleistocene populations. In adaptive terms, it is really true -- we're more different from early "modern" humans today, than they were from Neandertals. Possibly many times more different.
Now take a look at my recent post on deep history...
... Even after the development of agriculture and writing we see thousand year intervals of relative stasis in China, Egypt and Mesopotamia. How could this be when our fundamental technologies change in decades. Are the minds of modern Egyptians radically different from the minds of only 6,000 years ago? Why? Why do we see this graph at this time in human history?...
Why do we go from steam engines to iPads in a few human lifespans? Why do we have so much schizophrenia and autism? Our brains have been rewired at top speed; accidents are common.

A big day in science, a big day for Darwin, a bad day for creationists. The Neandertals, of course, must have had souls ...

Update: More from Carl Zimmer. When I wrote the above sentence about autism and schizophrenia, much less the original post some years ago, I didn't know this ...
If you believe the difference between humans and Neanderthals is primarily in the way we think, then you may be intrigued by the strongly selected genes that have been linked to the brain. These genes got their links to the brain thanks to the mental disorders that they can help produce when they mutate. For exampe, one gene, called AUTS2, gets its name from its link to autism. Another strongly-selected human gene, NRG3, has been linked to schizophrenia...
So the brain changes that occurred after Neandertal, in the time of deep history, have associations with the disorder of schizophrenia and autism.

In 2007 I wrote: Is schizophrenia the price we pay for an evolving brain? and I speculated that we could consider autism and schizophrenia to be "evolutionary disorders".

Update 10/6/2010: Clearly prescient: Your Mother Was a Neanderthal #4 (Time Warp Trio). Also, Robert Sawyer must be feeling cheerful today. Lastly, do read the whole Hawks essay. There were a lot of hominin-variants roaming the world 50,000 years ago, and they were likely "dynamic" (or at least - kinetic). We need a word with less historic baggage than "breed" to replace "species" in this discussion.

Update 10/7/2010: The Economist has a good summary, with more on what I've been calling evolutionary disorders.
... But an examination of the 20 largest regions that have evolved in this way shows that they include several genes associated with cognitive ability—and whose malfunction causes serious mental problems. The presence of an extra copy of DYRK1A is linked to Down’s syndrome; mutation of NRG3 is linked to schizophrenia; mutations of CADPS2 and AUTS2 are linked to autism. These four genes therefore look like good places to start the search for modern humanity’s essence...
Incidentally, I did a google search on "evolutionary disorders" and the term has been in use for a year or two. I had the earliest hit I saw though!

Zimmer's article has the clearest overview so far, with a balanced review of the scientific debates.

1 comment:

Paul said...

That is a very interesting paper you’ve assembled and although I bring no professional – or even personal – experience to your proposition it just strikes me as right. In fact I’d go so far as to say it’s so right it’s obvious.

It also makes me wonder if the staggering increase in incidences or clinical depression (or bi-polar disorder, if you prefer) are explained by some peoples’ inability to cope with [modern] life. The changes made in living from the time of the steam engine to the time of the ipad are, I suggest, too much for some people. They literally cannot cope with the pace of [modern] life.