Continuing our series of Big Science Questions, Mark Buchanan asks if we are in a post-evolutionary age, and Michael Ruse looks at our role in change.
Comments that followed the death of Stephen Jay Gould last week show that research into our evolutionary beginnings still excites great controversy among academics, but what about the future? Are we still evolving? Most people know that the main causal mechanism of evolution is natural selection, whereby there is a "differential reproduction" of organisms, with only the successful (the "fittest") passing on their heritable characteristics to future generations.
Many people think that, thanks to modern civilisation, humans today are largely free from natural selection and that evolution is therefore finished. But, as Charles Darwin himself realised and discussed somewhat gloomily in The Descent of Man , there is more to evolution than natural selection. There has to be raw variation on which selection can work. If everything and everyone were identical, there could be no differential reproduction, and evolution would indeed grind to a halt.
Although Darwin did not have much idea about the causes and nature of this variation - today we think it comes through mutation, which ultimately goes back to random changes in DNA - he realised fully that if you stopped or relaxed natural selection, evolution would continue (or perhaps restart). If new variations constantly enter populations of organisms, and there is no selection directing or removing them, these variations will quickly cause overall changes.
Darwin's big worry was that modern medicine would mean that many people - people who have new or inherited deleterious variations - would survive and reproduce, whereas before they would have died as children and failed to pass on these unfortunate features. He did not want us to stop helping the sick and ailing, and he would have been appalled at the idea that we might coerce people into forgoing reproduction, but he did point out that we would never let such bad practices persist in our domestic animals and plants.
Although I think Darwin was right in his science - protecting people from the forces of selection simply means that evolution goes in other ways - I am not as worried as he about the consequences. I use beta blockers for high blood pressure, but they are just as much a part of my environment as were the high-cholesterol school lunches of my youth. Just as human culture has changed the forces of evolution, so it can protect us from the side-effects of these changes.
Nevertheless, natural selection does still occur, even in the first world. Disease has always been a major factor in human evolution and, given that we are a social species, we have often acquired new, natural protections to life-threatening invaders. In the 19th century, tuberculosis was a killer, especially as people moved to cities where infection spread that much more easily. Epidemiologists, however, saw that natural resistance to the disease started to kick in, even before the advent of medical methods of treatment. Similar forces are at work today. One possible instance is among Aids sufferers in Africa. Some people have a greater natural immunity to the HIV virus, and it will be their offspring who survive and reproduce in greater numbers.
Another big, continuing evolutionary change comes thanks to modern travel, education and social mingling. The differences between races are starting to break down through interbreeding. Biologically, Jews are not that different from Gentiles, but in the US even these differences are being obliterated as the grandchildren of the ghetto rush into unions with the Protestant and Catholic offspring of Britain and the rest of Europe. The recent US census tells us that a similar pattern is to be found between the children of orientals and the children of occidentals. These are what you might call relatively natural evolutionary processes - at least, unplanned evolutionary processes.
Since the time of Darwin, "eugenicists" have dreamt that we humans might take control of our evolution and mould it for better ends. Of course, there is considerable doubt as to what constitutes a "better end", and the legacy of the Nazis means that few are willing openly to endorse deliberate, racial-breeding practices. Moreover, human nature is a fairly strong conservative force.
Nevertheless, some kinds of biological population-shaping are occurring today and look likely to increase. Take sex selection. In parts of the world, India notoriously, there is widespread use of techniques for discovering a foetus's sex and aborting if it is not the desired one - which in practice almost inevitably means aborting if the foetus is not male. At the population level, this is bound to have significant effects on sex ratios (normally, roughly 50-50) and will have major trickle-down social effects.
The Human Genome Project is just about finished, and we have a map of the genetic nature of humankind. Thanks to this, you might think that even if conventional human evolution is fairly slow and perhaps stagnant, in the immediate future there will be a new, very rapid and dramatic form of evolution. Through manipulation of our heredity, it may be possible to bypass the conventional methods of reproduction and design the kind of traits we want for our successors. At a minimum, we could try jiggling around with our existing frames, extending or perfecting the desirable features already possessed. Most people of my generation will live longer than our parents because of better nutrition and related environmental and cultural changes - quitting smoking, most significantly.
Perhaps we might aim for a biologically based greater longevity. Yet, even something as modest as this could have rather strange side-effects. It could be a classic case of Greeks bearing gifts. If we are going to live to, say, an average of 100 years rather than an average of 75, then I for one would hope that this would be accompanied by a little adjustment of the workings, or non-workings, of the lower back - maybe a stockier more forward-leaning frame, a longer, more twisted neck and shorter legs? Perhaps, after all, a short life and an upright one has things to be said in its favour.
The big thing about human evolution, however, is that it has moved from the biological to the cultural. We have not grown feathers, but we can fly. We have not developed bigger mathematical brain modules, but we can do calculations at far greater rates than ever before. We have no bigger talons or teeth, but we can kill by the millions. Here is the real point of human evolution today. This is why the human species floods the earth.
But my intuition is that biological evolution is crafty and conservative. After 3.75 billion years of change, nature has learnt that it cannot afford to be seduced irretrievably by the latest great breakthrough in the selective process. There have to be safeguards to see that things do not go too fast and that tried and true ways can endure. Hence, one should not assume that culture is all-conquering. But it succeeds best when it works with biology rather than against it.
Consider those weird perversions of Christianity that came forth from 19th-century America. The Shakers proscribed sexual intercourse, and now they are down to two or three aged members, their sect remembered chiefly for its beautiful furniture. Saints and politicians try to change things, especially biologically encoded things, but they do not often succeed. Feminists have spent the past few decades trying to change the ways of men, with debatable success. Bill Clinton was not much different from John F. Kennedy, who was not much different from many of his predecessors. The hypocrisy factor may have risen, but the inclinations and behaviour remain unaltered.
The point is that we are evolving culturally, but that you should not necessarily think that this at once translates into biological evolution. Or more important, you should not think that cultural evolution can go as fast as it likes in whatever direction it likes. Evolution is a blind, thoughtless process. Those who speak of the "wisdom of the genes" do so metaphorically, and it is a mistake to conclude that any tampering with what nature has produced has to be wrong. However, natural selection is a relentless force, and successful organisms - and we humans are certainly successful - work as well as they do because their parts function together harmoniously. Change has to be gradual and relatively smooth rather than sharp and jerky. But, having said this, change is what evolution is all about. Humans are the product of evolution, and there is good reason to think that our evolution is still in action. In part, this action is outside our control. In part, it is inside our control. But which part is which, and whether we have the power to move the parts around at will is another question.
Michael Ruse is professor of philosophy at Florida State University. His appreciation of Stephen Jay Gould can be found in The THES common room at