Tuesday 11 December 2007

Pic of the day: I won't even touch the area of sexual selection, one of the most rapid drivers of evolution.

Evolution in overdrive

Rapid acceleration in human evolution described in Reuters Science News: "In fact, people today are genetically more different from people living 5,000 years ago than those humans were different from the Neanderthals who vanished 30,000 years ago, according to anthropologist John Hawks of the University of Wisconsin."

OK, that is probably over the top. Hopefully this is a misunderstanding and he meant Cro-Magnon, the ancestral European race that replaced the Neanderthals. You see, the Neanderthals are now widely consider a different species, evolved separately from a common ancestor, living on their own for 600 000 years or so. They were visibley different in many ways: Far more muscular, stockier, with a more solid skeleton to anchor their bulging muscles. Their brain was larger but mainly in the back of their heads, with their forehead lower and sloping except for large brow ridges. They would have attracted some curious stares on the street even if in suit and tie, I think. To say nothing about their culture, but then again we didn't have much of that either until 60 000 years ago, perhaps a bit less.

On the other hand, there really is a profusion of new genes around the world. Our species has exploded unto an empty scene, and as always when some life form breaks out of a bottleneck, there is a flurry of adaptations to the new niches. If we see the whole species as one, I can certainly believe that there are more accumulated mutations in the last 5000 years than the previous 600 000. But probably not in each lineage.

The mutations that have been identified so far mainly fall into two broad categories: Adaptation to diet, and resistance to diseases. As we settled in different areas, being able to metabolize the local plants became particularly useful. And at least three different places saw humans grow the new ability to drink milk throughout their lives rather than just as babies. This ability was probably crucial to make the current Europeans - and their cousins in India - become dominant in that area. But there are other less remarkable adaptations. Each region has its favorite grains, for instance: Wheat in the Mediterranean and Middle East area, rice in East Asia, Maize in the Americas. There are subtle differences among them, and being able to digest and metabolize one of them more perfectly can give a great boost to your genes. Or could during the lean times that lasted until just recently.

One example that I have described in connection with my own life is the way animal farmers and grain farmers have developed different preferences in metabolizing sugar and fat. For animal farmers, including my ancestors on both sides, fat is fairly plentiful. Milk, meat and even pure fat from around the kidneys and intestines were crucial calorie sources during the winter and spring. For the grain farmers, however, fat was rare, while grain was the staple food all through the year. What little fat was in their diet needed to be saved for essential use in the body tissues (brains, for instance, consist mostly of fat and water). So they will tend to put on weight more easily these days, as their bodies still believe fat to be a precious commodity that needs hoarding. We children of the herders will happily burn fat as we get it, gaining weight more slowly. Dietary fat also has less influence on our hearts and blood vessels.

The human immune system may have evolved more rapidly than any other part of us. There is also a slightly controversial theory that women prefer to mate with men whose immune system is widely different from their own, out of some instinct to give their children the best possible arsenal of immune responses. (Mice do this too.) Evidently the attraction to men with a different immune complex is strongest around the time of ovulation. Of course women aren't entirely in the grip of their instincts (well, most of them aren't) but enough that it can be traced in statistics. You may say that it kicks in "all other things being equal and sometimes even when not".

The study does not cover these more controversial ideas, and it is very very quiet about the possibility that brain function could be one of the areas selected for rapid evolution. Some scientists believe that living in a civilization, interacting with far more people, could put a strong selective pressure on intelligence. This seems likely, for certain values of intelligence. On the other hand, living "in the wild" means you have to memorize what kind of food is edible, what is toxic, what fruits or roots grow where at what time of the year, and the behavior of various prey animals. It seems likely that civilization would require not so much "more" intelligence as a "different" intelligence, one with less focus on memorizing concrete details but more focus on inferring relationships.

In any case, the topic is so controversial that it will probably not see much publicity for a long time. This is partly due to the horrors of eugenics gone wild before and during World War II. But not least it is because of America's legacy of slavery. The notion of black Africans as stupid and lazy was easy to sustain during the age of slavery: Who would not be stupid and lazy after a day of hard work and too little food, not to mention no education? Given that slave owners probably bred for physical strength and low intelligence, the amazing thing is that the blacks in America have bounced back as quickly as they have. It seems to support the notion that our current civilization is not even using all of our inherent mental capacity.

In any case, intelligence is a trait that is easily masked by culture, at least compared to puking when you drink milk or writhing in pain after eating beans. There are no doubt many other genes not represented in a sample of 270 people. As we moved toward a near future where it is normal to have your genome analyzed, a wealth of new information is likely to come to light. And we will see both how different we are - every one of us is a mutant - and how similar we are after all. Because even today, the genetic variation between two of our "races" is less than is found within a single tribe of chimpanzees. We are still a young race, and all of us are close relatives. It is something we should never forget, even in an age of mutants.