Thinking about chimpanzees again:
We have thought about chimpanzees in two contexts. They do not have some of the genetic advantages that we have, and they do seem to engage in warfare. More evidence has accumulated.
I have pointed out that we humans have physical capabilities, the better ability to run and swim, to endure heat and cold and starvation and thirst, to climb most obstacles and probably better balance, that a chimpanzee would find quite useful. I put this down to the fact that genomes of most animals have been optimized, so that there are tradeoffs, one ability being sacrificed for another more valuable. The thing we appear to have traded off for a lot of our abilities is a robust immune system. We do not need it because we are not promiscuous; at least those of us who have offspring in the long run are less promiscuous than chimps. The cad is the loser. True love has made us human.
Scientists are looking ever more closely at the specific differences between our DNA and that of chimps. (What Makes Us Human? Katherine S. Pollard. SCIENTIFIC AMERICAN volume 300 number 5 May 2009 page 44. Unsurprisingly, the answer offered is not true love.) It turns out that we share all but 15 million base pairs, out of 3 billion, with chimpanzees. And now they are beginning to take seriously what used to be called “junk DNA,” which is to say DNA that does not code for the manufacture of a protein in the classical way. It has turned out that only 1.5 % of our DNA is classical genes.
Imagine that you are a character in a 1950’s science fiction film, and some harmless aliens have built a flying saucer factory. The aliens were called away to rescue some other planet, leaving their factory behind, which soon became declared an eye sore. You purchased it with the understanding that you would destroy it immediately, so being busy, you send in a crew of men to collect everything of value and destroy everything else. When you meet with them they produce drill presses, lathes, metal stamps, welding equipment and so forth. When you ask for the plans, they shrug that there was indeed a lot of paper left behind, but it seemed of no value since it already had writing on it so they did not keep it. You are understandably disappointed. The tools, the equivalent of the genes, are fine so far as they go, but you are not going to be able to build your flying saucers without knowing how to use those tools. That is what the 98.5 % of our DNA does.
Katherine Pollard looked closely for places where our DNA differed the most from chimpanzee DNA and found such regions. The most conspicuous had something to do with the formation of the brain. It also, and this is tantalizing since it bears on fertility but I have no idea what it means, has something to do with sperm production.
Other regions coded for hand structure and for digesting starches and milk. Chimps don’t get fries and a milkshake very often.
And indeed there were changes in the immune system. One of interest is a change that makes us resistant to a virus they call PrEV1. There is a change in our DNA that makes us more resistant than chimpanzees are to the virus. The same change also made us more vulnerable to the HIV virus than they. This is interesting, because it is a clear case of a genetic tradeoff, sacrificing one ability to gain another.
An article called “An Advantage of Promiscuity” in NATURE was where I learned that humans have the weak immune system of monogamous primates, not the robust one of promiscuous ones. To my mind the title suggests that an advantage of a crime wave is you get a much better police force. At all events, the logic seems to me to indicate that we abandoned some of our immunity to gain other abilities, and in that case it should be possible to find regions of our DNA that are concerned with immunity that have undergone “accelerated evolution” with greater than average change from the apes, but which in fact are simply deteriorating. It would be easy to tell the difference. A region undergoing accelerated evolution because of positive selection should show about the same change appearing in everybody, where an abandoned site would show changes in any number of directions. I do not know whether this has been found, but I shall inquire and if I learn anything I shall let you know.
In the same issue, (The Planning of the Apes. Coco Bayllantyne. SCIENTIFIC AMERICAN volume 300 number 5 May 2009 page 27.) there is a story about a chimp in a Swedish zoo that spends the morning gathering rocks up to the size of dessert plates and then at 11:30 AM throws them at people. This shows he can plan. But he never hits anybody, which they say is because he has bad aim. I hesitate to add better throwing to the skills we have. Since the zoo is in Sweden, it seems likely that the animal has always been treated gently and has no intention of actually hurting anybody. It would be rather idle but sort of fun if somebody would actually see how well a chimp could be taught to throw a baseball.
Meanwhile on the issue of whether chimps fight wars, it has been baldly stated that they only do so if humans have encroached on their habitat. (ECONOMIST volume 390 number 8624 March 28, 2009 page 91.) However, since people seem to be encroaching on their environments everywhere, and if there were no humans around the behavior would be hard to observe, the issue seems a little problematic. And opinion is not unanimous. (Taming the Urge to War. John Horgan. SCIENTIFIC AMERICAN volume 300 number 5 May 2009 page 16.)
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