On Darwin’s voyage, he observed ostriches and rheas living on grasslands on separate continents. These two types of birds are similar, but not identical. How did Darwin apply these observations?

Which of the following factors would not contribute to allopatric speciation? a) a population becomes geographically isolated from the parent population.b) the separated population is small, and genetic drift occurs.c) the isolated population is exposed to different selection pressures than the ancestral population.d) different mutations begin to distinguish the gene pools of the separated populations.e) gene flow between the two populations is extensive.