Like Prof Steve Jones before him, Sir David Attenborough has argued that humanity has now escaped nature's clutches, and we have now stopped evolving. Masters of our own destiny, as a species we have confronted the four horsemen of the apocalypse, and emerged victorious.
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.
At a British science festival event on Sunday, I was one of a group of four evolutionary scientists who presented their latest research to an audience of festival attendees, from whom we took an array of enthusiastically proffered questions. We had specifically set out to address the question: "Are we still evolving?" The conclusion, from all four of us, was a resounding yes.
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 around the world over recent decades and 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.
What it is ultimately interested in is the number of descendants an individual produces who can then pass on their genes. So long as some people are having children and some people are not, natural selection has something else to which it can turn its attention. And – as Prof Tom Kirkwood of Newcastle University explained to our audience, the fact that more people in European countries are delaying childbearing, piques natural selection's interest in the novelty of whatever genes they might be carrying.
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 this year, 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. As Dr Pascale Gerbault of UCL told us, 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. Natural selection chose more modest dentition than our hominid ancestors. Another example: as west African farmers began to farm yams thousands of years ago, they inadvertently changed the landscape so that it supported populations of malaria-carrying mosquitos, which then led to natural selection for individuals carrying the sickle-cell allele because it granted some individuals immunity to malaria.
As malaria prevention and treatment improves, we can expect that the otherwise harmful sickle-cell allele will decline in frequency, though there are no studies as yet that have confirmed this. Thousands of years are to evolution a mere blink of an eye, and so a longterm view is necessary if we are to fully appreciate our place in natural history. Similarly, we need to consider our species as a whole, inhabiting a range of environments, not just one western educated industrialised rich democratic (Weird) niche. As Dr Andrea Migliano of UCL pointed out, there are many populations around the world experiencing a range of environments, all subject to natural selection in slightly different ways.
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 completely useless in the long run. Prediction is very difficult, especially when it is about the future. Furthermore, the assumption that human evolution can ever reach an endpoint fails to appreciate the dynamism of both nature and of humanity.