Like birds and mammals that eat the fish and insects, and you get trees and plants that begin to grow near the standing water that can't grow near the running water.
Another thing would be, if a hatchling gets separated from the rest of its family, once the others get far enough away, its survival instinct kicks in.
As the match began, I was alarmed to see that the other team was wrestling without headgear, a kind of light helmet designed to protect a wrestler"s ears.