Famines in the context of Population bottlenecks

Geologically one of the youngest inhabited territories on Earth, Easter Island (also called Rapa Nui), located in the mid-Pacific Ocean, was, for most of its history, one of the most isolated. Its inhabitants, the Rapa Nui, have endured famines, epidemics of disease, civil war, environmental collapse, slave raids, various colonial contacts, and have seen their population crash on more than one occasion. The ensuing cultural legacy has brought the island notoriety out of proportion to the number of its inhabitants.

Throughout Russian history famines, droughts and crop failures occurred on the territory of Russia, the Russian Empire and the USSR on more or less regular basis. From the beginning of the 11th to the end of the 16th century, on the territory of Russia for every century there were 8 crop failures, which were repeated every 13 years, sometimes causing prolonged famine in a significant territory. The causes of famine were different, from natural (crop failures due to drought or disease) and economic and political crises; for example, the Great Famine of 1931–1933, colloquially called the Holodomor, the cause of which was, among other factors, the collectivization policy in the USSR, which affected the territory of the Volga region in Russia, Ukraine and Kazakhstan.

A population bottleneck or genetic bottleneck is a sharp reduction in the size of a population due to environmental events such as famines, earthquakes, floods, fires, disease, and droughts; or human activities such as genocide, speciocide, widespread violence or intentional culling. Such events can reduce the variation in the gene pool of a population; thereafter, a smaller population, with a smaller genetic diversity, remains to pass on genes to future generations of offspring. Genetic diversity remains lower, increasing only when gene flow from another population occurs or very slowly increasing with time as random mutations occur. This results in a reduction in the robustness of the population and in its ability to adapt to and survive selecting environmental changes, such as climate change or a shift in available resources. Alternatively, if survivors of the bottleneck are the individuals with the greatest genetic fitness, the frequency of the fitter genes within the gene pool is increased, while the pool itself is reduced.

The genetic drift caused by a population bottleneck can change the proportional random distribution of alleles and even lead to loss of alleles. The chances of inbreeding and genetic homogeneity can increase, possibly leading to inbreeding depression. Smaller population size can also cause deleterious mutations to accumulate.