Generally speaking, we tend to think of evolution in purposeful terms: There must be a reason for difference, an explanation grounded in the chances of passing on one’s supposedly selfish genes. Perhaps those olive feathers provide a better camouflage amidst Finnish vegetation, or have come to signify virility in that part of the world.
As evolutionary biologists Suzanne Gray and Jeffrey McKinnon describe in a Trends in Ecology and Evolution review, differences in color are sometimes favored by natural selection — except, that is, when they are not.
Often differences in color do not have any function at all: they just happen to be. They emerge through what’s known as neutral evolution: mutations randomly spreading through populations.
At times, this spread, this genetic drift, evenly distributes throughout the entire population, so the whole species changes together. Sometimes, though, the mutations confine themselves to different clusters within a species, like blobs of water pooling on a shower floor.
Given enough time and space, these processes can — at least theoretically, as experiments necessary for conclusive evidence would take millennia to run — generate new species. Such appears to be the case with greenish warblers living around the Tibetan plateau, who during the last 10,000 years have diverged into multiple, non-interbreeding populations, even though there are no geographic barriers separating them or evidence of local adaptations favored by natural selection. The raw material of life simply diversified. One became many, because that’s just what it does.
Read the full, original story: Evolution’s contrarian capacity for creativity