A population of pigs live on an island together with burrowing termites. Pigs that have the longest snouts tend to survive more frequently than those with shorter snouts. Over time, most of the pig population is made up of individuals that have very long snouts. This an example of which type of variation?

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.