For most of our evolutionary past, humans hunted and gathered their food, living in small groups on the African veld. By 2 million years ago, our ancestors had shifted from a mostly vegetarian diet to eating plenty of meat. Yet agriculture only stirred 12,000 years ago at the earliest.
At most, our ancestors have farmed for only 0.5 percent of our history as modern humans. You can see why many evolutionists assume all the interesting stuff happened before the agricultural revolution. It’s an assumption that sits well with folks who are willing to accept the importance of evolution but get a bit squeamish about natural selection being something that’s happening to them.
A few weeks back I wrote about how selection is always acting to stabilise the sex ratio near 50:50. It’s a fact so obvious that it escapes our notice, brought to you nonetheless by natural selection. And molecular analyses are starting to report the statistical signature of recent selection on gene frequencies.
But we’re mostly still in the dark about just how strong post-agriculture natural selection has been. Perhaps cultural and economic changes, including the spread of monogamous marriages, had such influence over survival and reproduction that they obliterated any action of natural selection?
Fortunately a small group of biologists spend their time not in the field, but in archives, where they ferret out historic records of recent human populations for evolutionary analysis. One such group, led by Dr Virpi Lummaa, has been especially successful studying the records kept by Lutheran parishes in pre-industrial Finland.
This week, Lummaa and collaborators Alexandre Courtiol, Jenni Pettay, Markus Jokela and Anna Rotkirch report in PNAS that selection on a group of 5,923 Finns born between 1760 and 1849 is comparable with the stronger estimates from wild animal populations.
Their method dissects the contribution of survival to maturity, success in marrying, number of marriages and the number of children born to each individual. Only about 60 percent of children lived to 15 years of age, and so child survival had a big effect on the overall estimate of selection.
Their estimates also confirmed another prediction from evolutionary theory: that men vary more in mating success than women. More males than females failed to have any children. Men who did marry several times had more children than those who married only once, but this relationship was weaker for women.
There’s much more to the paper, and it is getting lots of popular press if you want to read more. One of the paper’s main virtues, in my opinion, is as an illustration that the opportunity for natural selection to act did not somehow weaken with the advent of agriculture or the spread of monotheism and monogamy. These communities, and millions of others for which we have no such detailed records, experienced just as much evolutionary activity as any other animal living in its natural environment.
Their results add serious quantitative weight to the idea that human evolution continues as relentlessly as ever. Probably more so as people adapt to rapidly changing conditions. Henry Harpending and Gregory Cochrane, in The 10,000 Year Explosion argue that agriculture, far from slowing human evolution, propelled it ever faster.
And I’d be willing to bet a case of Pinot that when the modern data-rich world coughs up suitable information about our current generation, the opportunity for selection will be at least as strong as it was in pre-industrial Finland.
What are your predictions for contemporary evolution of humans?
Comment here or Tweet @Brooks_Rob #naturalhistoryofpresent