Question

so what was the reason that the two populations developed different traits? why did different traits emerge in the two populations of finches separated by the mountain range? the climate was different on both sides. the two bird populations stayed the same the whole time. only birds on one side of the mountain encountered a new food source that forced the population to shift their traits. the other birds did not change. both populations were affected by a pressure of natural selection to adapt to a new food source. sexual selection favored the large beak trait on the west side of the island and the small beak trait on the east side.

Explanation:

Natural selection occurs when organisms adapt to their environment for survival and reproduction. Different environmental pressures, such as availability of food sources, can lead to different traits being favored in separated populations. In this case, if both populations faced a new food - source pressure, natural selection would drive them to adapt with different traits.

Answer:

Both populations were affected by a pressure of natural selection to adapt to a new food source.