Nya rön, nya utmaningar
Människans evolution har inte bromsats, utan tvärtom gått snabbare de senaste 10 000 åren. Den större populationen, och den vidare spridningen över klotet, har skapat allt fler urvalsmekanismer eftersom människan utsatts för olika varianter och grader av evolutionärt tryck.
Det påstås i den nya studien Recent acceleration of human adaptive evolution (pdf), som publiceras i PNAS av en sammansättning antropologer och genetiker, bland annat professor Henry Harpending.
Ur pressmeddelandet:
"We used a new genomic technology to show that humans are evolving rapidly, and that the pace of change has accelerated a lot in the last 40,000 years, especially since the end of the Ice Age roughly 10,000 years ago," says research team leader Henry Harpending, a distinguished professor of anthropology at the University of Utah.Den åttasidiga studien går naturligtvis in mer på detaljer, men diskussionsdelen är ganska begriplig:
Harpending says there are provocative implications from the study, published online Monday, Dec. 10 in the journal Proceedings of the National Academy of Sciences:
"We aren't the same as people even 1,000 or 2,000 years ago," he says, which may explain, for example, part of the difference between Viking invaders and their peaceful Swedish descendants. "The dogma has been these are cultural fluctuations, but almost any temperament trait you look at is under strong genetic influence."
[T]he Neolithic and later periods would have experienced a rate of adaptive evolution more than 100 times higher than characterized most of human evolution. Cultural changes have reduced mortality rates, but variance in reproduction has continued to fuel genetic change. In our view, the rapid cultural evolution during the Late Pleistocene created vastly more opportunities for further genetic change, not fewer, as new avenues emerged for communication, social interactions, and creativity.Om forskarnas tes håller får det naturligtvis stora följder för hur vi betraktar varandra på den här planeten. Som LA Times skriver:
Most of the genetic changes the researchers identified were found in only one geographic group or another. Races as we know them today didn't exist until fewer than 20,000 years ago, when genes involved in skin pigmentation emerged, Hawks said. Paler skin allowed people in northern latitudes to absorb more sunlight to make vitamin D.Inte minst kommer rasister, som ju anser att olikheter mellan människor gör att vissa är sämre än andra, försöka dra nytta av de nya rönen. Plötsligt kan vi åter befinna oss i en situation där vetenskapen kan tyckas ge stöd åt generaliserande antaganden, som att spanjorer är eldiga, men som om något säger väldigt lite på det individuella planet. Det ligger en stor utmaning i detta, för oss som argumenterar för människors lika värde. Rimligen ligger lösningen i att alltid betrakta och bemöta människor som individer.
"As populations expanded into new environments, the pressures faced in those environments would have been different," said Noah Rosenberg, a human geneticist at the University of Michigan, who wasn't involved in the study. "So it stands to reason that in different parts of the world, different genes will appear to have experienced natural selection."
