By Susan Milius
A pair of decades-long studies of birds moving into other birds’ neighborhoods show that immigration can have a quirkier effect than predicted by the usual textbook view.
Evolutionary biologists have often talked about two forces working against each other in shaping the mix of genes in a local population. Natural selection adapts a population to its particular home. Yet immigration, bringing in genes from outsiders, can overwhelm the effects of that fine-tuning and make diverse populations more alike.