Sockeye Salmon of Seattle and Evolution
In 1937, a batch of sockeye salmon were added to Lake Washington in Seattle. By 1992, the fish had formed into two distinct groups that looked different from each other and would not interbreed. This is the definition of separate species, and indeed scientists have given one of the fish groups a new name!
While all of the initial fish were from the same species, when they arrived in Lake Washington, one portion of the school decided to settle near a beach. They laid their eggs along the beach and began to evolve to fit in well with their beach-side existence.
The second group chose instead to move into the nearby river that feeds the lake. Because their breeding ground was in a fast-moving river, their breeding techniques as well as their appearance both began to change to suit this different environment.
In only just over 50 years, those two environments were having a serious effect on the two groups of fish. Not only were physical changes obvious between the two groups, but also the groups did not interbreed at all any more. The river-breeding fish did not try to intermingle with the beach-breeding fish.
The salmon are now the object of much research, as scientists track the changes between them, and watch as the two groups become more and more distinct from each other.
Lisa's Biology Pages