Northern elephant seals have reduced genetic variation because of a population bottleneck inflicted on them in the 1890's by humans. Hunting reduced their population size to 20 individuals at the end of the 19th century. Although their population has rebounded to over 30,000 , but their genes still carry the marks of this bottleneck and they have much less genetic variation than a population of southern elephant seals that was not so intensely hunted.
Big losses of genetic variation for the small populations are readily caused by
A) gene flow.
B) genetic drift.
C) natural selection.
D) the founder effect.

Genetic drift is a mechanism of evolution characterized by random fluctuations in the frequency of a particular version of a gene (allele) in a population.

There are two major types of genetic drift: population bottlenecks and the founder effect.

A population bottleneck is when a population's size becomes very small very quickly. This is usually due to a catastrophic environmental event, hunting a species to near extinction, or habitat destruction. When the size of the population is reduced so quickly, many alleles are lost and the genetic variation of the population decreases.

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