Surfing the Wave

Cane toads, to general dismay, have been spreading rapidly in Australia. And in the course of that spread, they have evolved.  This is particularly true at the front of the wave of toads.  Those leading-edge toads have longer legs, are more active at night, and have higher reproductive rates.

Something similar has happened in Quebec, where a few thousand French colonists grew more than a thousandfold over  three centuries. A research team led by Damian Labuda, Helene Vezina, and Laurent Excoffier  (lead author, Claudia Moreau)  found that people living near the wavefront contributed significantly more ancestry to the modern Quebec population than those from the central regions. Moreover, fitness was heritable on that wavefront – so life-history traits measurably evolved during the Quebec expansion.  Just as they have in cane toads.

This doesn’t surprise me –  I would expect to see a noticeable evolutionary response to any major ecological shift that persisted very long.  In fact,  the impact of a big population boom like this is limited by the fact that booms always end, which should reverse the selective pressures.  There should be a larger response to changes that persist.  Thus you would expect larger changes as the result of the transition from hunter-gatherers to  farmers, since people continued to be farmers for thousands of years.

The paper is also notable in that we see Laurent Excoffier saying that there has been noticeable recent evolutionary change in a human population – a change that has not occurred in all human populations. I had gotten the impression that he really did not like that kind of conclusion, which is too bad for him, because such change is ubiquitous. Maybe we’ll hear more such results from him: once you accept it, the dark side is with you forever.