Examine the following scenario: A population of small fish lives in a lake (Lake A).The dark-colored fish are the ancestral phen
otype and represent the usual coloration of the species. The bright-colored fish, however, arose over time. There is a steady rise in the population of bright-colored fish. Both populations thrive. Suppose that a short land barrier separates Lake A from another small lake with a population of only the normal dark-colored fish (Lake B). After torrential rains lasting for days, the lakes overflow and a few of the bright-colored fish from Lake A are washed into Lake B. List the sequence of evolutionary mechanisms which have come into effect in each event.
The rise of the bright colored fish is an example of variation in the natural selection process of evolution discovered by Darwin and Wallace. All species of living organisms develop varieties. If the variety is favorable to the environmental conditions, then it will thrive and in that way be selected to survive and help propogate the species. The accidental mixing of the waters between the two lakes is an example of how environmental conditions can change in nature and thus effect the survival of the varieties. If the bright colored fish are then living in the same lake as the dark colored fish then they will probably effectively compete for survival in the Lake B according to the above mechanism.
