Attenborough is wrong. Humans are still evolving
Like Prof Steve Jones before him, Sir David Attenborough has argued that humans have stopped evolving physically and genetically because of birth control and abortion, but that cultural evolution is proceeding "with extraordinary swiftness".india Updated: Sep 13, 2013 02:24 IST
Like Prof Steve Jones before him, Sir David Attenborough (http://tinyurl.com/pqsjgnf) has argued that humans have stopped evolving physically and genetically because of birth control and abortion, but that cultural evolution is proceeding "with extraordinary swiftness".
So have we, in Attenborough's words "put a halt to natural selection", the major force of evolution, which drives adaptation, creating and destroying exquisitely variable species at its whim? The short answer is "no".
In fact, there is not a population on the planet that is free from the forces of nature in this way, and in fact it is hard to imagine how there ever could be.
Attenborough and Jones are right about one thing - natural selection requires variation. It needs some individuals to thrive more than others. So the improved survival prospects over centuries drastically decreases the potential for natural selection to work in those populations.
But this is not the end of the argument. Even if everyone survives to the same age, there is still variation for natural selection to work with. Natural selection doesn't really care about survival.
Another problem with the argument that populations with high survival rates have escaped natural selection comes from the fact that as we change our environments, they become something to which we are no longer well adapted, again catching the beady eye of natural selection.
As I argued earlier, changes to infrastructure, sanitation and medical care not only improve survival - they also change the way that natural selection operates on those who do survive.
Such changes show how the evolutionary experience of humans is entwined with cultural changes in habits and traditions. These variable human qualities are why a third of humans have, over the past few thousand years, evolved the capacity to consume fresh milk as adults, which is to most mammals simply "baby food".
Human association with cattle and milk-drinking behaviour - a cultural trait - provided the environment that rapidly selected for the genes that allow lactose tolerance.
Similarly, the ancient innovation of cooking our food meant that our bodies no longer needed to spend scarce nutrients on growing powerful teeth and jaws to crush raw plant material.
Arguably, the lesson to be drawn from this global diversity is not that humans will diverge into several different species; instead, we must recognise that the unpredictability of human affairs means that our knowledge of natural selection in any specific human population right now will be useless in the long run.
Furthermore, the assumption that human evolution can ever reach an endpoint fails to appreciate the dynamism of both nature and of humanity.
First Published: Sep 13, 2013 02:21 IST