Nature & Environment
Evolution through natural selection
...accounted for.} The group B ponds allowed Endler to check whether any change observed in the group C ponds could have been due, not so much to the addition of a fish that preys on guppies, but to the addition of any other species of fish or even any other species of predatory fish (whether it preyed on guppies or not). {So again, the group B ponds serve as 'controls' for...