Tom Clarke has a background in zoology. After leaving the lab he worked on science radio and television programmes in the United States. He now writes about the latest research in science and technology for Nature magazine's 'Nature News Service'.

Has Human Evolution Stopped?
Between three and five million years ago the forces of nature drove our ape-like ancestors down from the safety of the trees and made them stand on their own two feet. These upright apes were then sculpted by natural selection into lankier, less hairy, brainy creatures.

Later, other natural forces, perhaps climate change, disease or even war relegated our cousins the Neanderthals to the evolutionary scrap heap while our species, Homo sapiens survived — but only just.

In the 500 thousand or so years we've been strolling the Earth Homo sapiens have been continually feeling the force of natural selection too. We were nearly snuffed out by an ice age and whole civilisations disappeared beneath floodwaters, volcanic ash or were wiped out by horrific diseases. Only those of us with good genes and good fortune survived to reproductive age and passed those genes on.

Now almost everyone in the developed world lives past reproductive age and improving healthcare and infrastructure in the developing world will surely mean that poorer countries will enjoy the same luxury. As people aren't dying until after they reproduce, bad genes and harmful mutations are passed on to the next generation. This surely flies in the face of natural selection — the survival of the fittest — meaning human evolution has come grinding to a halt?

In my opinion, no. In the developing world (which is most of the world) vast numbers of children die because of natural disasters, diseases and warfare —the same things that were killing our ancestors 500,000 thousand years ago. You only have to look to the HIV pandemic or drought induced famine for a very modern example of nature's selective forces at work. The case is perhaps harder to argue for those of us living in a sturdy house in a safe leafy suburb, with clean drinking water and private health care. Infant mortality is a thing of the past, major diseases are treatable and natural disasters largely avoidable, so the merciless selective forces of nature are something of an irrelevance.

Certainly, but that doesn't necessarily mean human evolution has stopped. I'd argue that technologically developed societies have merely slowed evolution down. But we can only keep nature at bay for so long. Take disease as an example; HIV is far from under control in the developed world and many experts predict that old enemies like influenza and tuberculosis are poised to make a comeback. After enjoying a century or two of the good life, with "bad genes" accumulating in our population, we will be a very soft target for a new disease outbreak or an unforeseen natural disaster. If our technologies fail to protect us against these forces of nature our genetic heritage could fail us too, meaning human evolution will return with a vengeance.

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Content last updated: 17/07/2006

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