Question

The following scenario is partly fictional: One million years ago, a small group of Homo erectus decided to follow a herd of wildebeest on a migratory path that took them much farther north than they had gone before. As they walked and walked, they decided that this new territory looked quite hospitable, and they decided to move their homes. One of the hunters went back to convince a few more Homo erectus individuals to join them. Ultimately, over 500 of them traveled north, and then far west for thousands of kilometers. They eventually ended up on a landmass that, as sea level rose, gradually became an island. Since they did not have boats, and couldn’t swim very far, these individuals couldn’t leave the island. Consequently, they never came into contact with the relatives that they left behind. Resources on this island were scarce, and there was intense selection against the bigger individuals who needed more calories just to survive. About 500,000 years later, the ocean levels dropped. Three foot tall hominids from the island then came into contact with five foot tall hominids on the mainland. They interacted much the way that olive and hamadryas baboons do – they mated. Using the Biological Species Concept, which of the following is illustrated by this scenario?

Allopatric speciation

Genetic drift

Sympatric speciation

Homo erectus became polytypic

Inheritance of acquired characteristic

Answer 1

This is an example of Genetic Drift. Genetic drift is defined as change in allele frequencies over generations. It is random and not due to natural selection. There are two types of genetic drift - Founder's effect and Bottleneck effect. In bottleneck effect, the population is drastically reduced and survivors establish a new population. In the above scenario, speciation occured due to Founder's effect where a small subgroup (random individuals) of the population migrated to a new landmass and colonized it. Over time, the subpopulation acquired varied characteristics such as height.

Allopatric speciation- In this type, the parent / ancestral population divides into two due to geographical barriers and become reroductively isolated. Gradually, the isolated populations diverge in terms of morphology and characters because of natural selection.

Sympatric speciation occurs within same geographic region as the individuals become reproductively isolated.  

Inheritance of acquired characteristic is based upon the use and disuse of organs while adaptation. The changes acquired are passed on to the offspring.