He was most impressed by the fact that polymorphism concealed powerful selective forces (Ford gave human blood groups as an example).

One major selective force on its emergence was climatic change.

Other selective forces may have operated quite recently and left a strong memory or image in the structure of the population's genetics.

Thus, we make no attempt here to examine in greater detail the selective forces that act on duplicated genes.

Dr. Michaelson admits that he has no idea what the selective forces are during development.

Hence selective forces would have favoured the most successful at doing it.

Thus, analysis of phylogenetic patterns gives insight into underlying selective forces.

The theory is not intended to deal with the possibility of gross external changes to the environment that bring new selective forces to bear.

Instead, current behavior is probably the result of selective forces that occurred in the Pleistocene.

I find the idea of a selective force implausible.