Have we stopped evolving? Whether the human race is still adapting to our surroundings is heavily debated – and now fresh genetic analyses by Harvard University’s Jonathan Beauchamp suggest natural selection still has a part to play.
Beauchamp, publishing in the Proceedings of the National Academy of Sciences, compared genomes and traits of 20,000 older people with the number of children they’d produced, and found natural selection favours less schooling and a higher age of first menstruation.
In 1859, Charles Darwin defined natural selection as “one general law, leading to the advancement of all organic beings, namely, multiply, vary, let the strongest live and the weakest die”.
The “strong” genes that help a species survive become more common over successive generations. Those traits – and any traits that arise from your genes – are called phenotypes.
Some people suggest human evolution came to a standstill between 40,000 and 50,000 years ago when modern humans emerged and started to control their surroundings.
Perhaps most famously Sir David Attenborough claimed in 2013 that we’d stopped evolving, telling British magazine Radio Times: “We stopped natural selection as soon as we started being able to rear 90-95% of our babies that are born. We are the only species to have put a halt to natural selection, of its own free will, as it were.”
Is he right? It looks unlikely. Recent studies have shown that our ability to process lactose, malaria resistance and adaptation to high altitudes are phenotypes that evolved relatively recently. And now Beauchamp has added more evidence.
He used a statistical test to analyse 20,000 Europe-descended Americans born between 1931 and 1953, part of the University of Michigan’s Health and Retirement Study. (They were chosen as their childbearing years were likely behind them.)
In terms of evolution, the more offspring a person has, the more times their genes can be passed on and the better their “evolutionary fitness”. When compared to the average brood for the population of their age, for instance, this is known as relative lifetime reproductive success.
Beauchamp looked at seven phenotypes in his cohort, including body mass index, height, first menstruation age, schizophrenia and education levels. These traits all have genetic roots – even educational attainment, shown to be the case in 2013.
He found people who had more kids – so were more evolutionarily fit – tended to have lower education levels, and the women were older at the time of their first menstruation.
But there are a number of limitations to the work, Beauchamp admits.
The Health and Retirement study only includes people aged 50 years or more. But 10% of females and 15% of males born in 1940 died before reaching 50 years.
Nor does it account for fertility timing. People with higher education levels tend to have children later, so end up with a smaller brood than if they’d started younger.
And a better indication of evolutionary fitness might be the number of grandchildren – or even great-grandchildren – a person has.