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12 December, 2006

Keeping On

Are human beings still evolving? Well duh! We’re still replicating, our genes are still mixing and mutating, therefore we’re still evolving. It’s amazing that anyone could ask such a question. A much more sensible question is: in what way are human beings evolving?

What brought this to mind was an article in today’s press about some research which shows that lactose tolerance – the ability to digest milk – has only arisen in some African populations in the past 3,000 to 6,000 years. It has only been a human trait in any population for 8,00 or 9,000 years – since people began keeping cattle. It is such a powerful survival advantage for pastoral peoples – estimated at a ten to one breeding advantage – that it has evolved separately in three or four places by different genetic mechanisms and has spread widely.

So, I ask myself, what are the evolutionary pressures on the world today? Obviously some of the killer diseases, like tuberculosis, malaria and AIDS are culling populations that would benefit greatly if they developed a resistance. Then there are the ‘epidemics’ of the modern, Western world – like obesity, asthma and depression – that we could use a few genetic tweaks to be rid of (or to keep on breeding despite them). Then there are the coming problems of global climate change and ever-increasing pollution levels. People who need less food, can breathe more particulates and tolerate more UV might have a distinct advantage.

On the other hand, one of the greatest barriers to reproduction has been education and increasing standards of living. The Western world is reproducing at well below the replacement rate (the rate at which the population would be maintained – about 2.1 children per female). In this situation, being poor and ignorant has a reproductive advantage which is being selected for even as we speak.

Trying to imagine what a human being five or ten thousand years from now might be like given today’s selective pressures is a bit depressing. It definitely won’t be the big-brained, scrawny types from 1950’s science fiction. I can see no pressures moving us in the direction of increasing intelligence. In fact, the opposite seems to be the case.

On the other hand, as we increasingly take our evolution into our own hands – through direct manipulation of our own genome – disease resistance, longevity, resistance to obesity, tolerance of environmental and man-made toxins, greater physical size, physical attractiveness, and so on will be what we aim for in ourselves (just as we engineer the same things in our food crops today). However, the idea that this will mean ‘the end of human evolution’ is stupidly naïve. Whatever we would like our genome to be, our environment will always have the last word.

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