Genetic erosion

Genetic erosion (also known as genetic depletion or genomic erosion) is any decrease in genetic diversity, both naturally occurring and human-caused. The term is sometimes used in a narrow sense, such as when describing the loss of particular alleles or genes, as well as being used more broadly when referring to the loss of a phenotype or whole species.

Genetic erosion occurs because each individual organism has a unique genome; if the individual dies without the chance to breed, any unique genes they carry are lost before they can be passed down to offspring. Two factors that compound and accelerate genetic erosion are habitat loss and habitat fragmentation–often brought on by development of agricultural and infrastructural areas–and low genetic diversity. Low genetic diversity is linked to inbreeding and a weak immune system both of which can then "fast-track" that species towards eventual extinction.

By definition, endangered species suffer varying degrees of genetic erosion. Many species benefit from a human-assisted breeding program to keep their population viable, thereby avoiding extinction over long time-frames. Small populations are more susceptible to genetic erosion than larger populations.

The gene pool of a species or a population is the complete set of unique alleles that would be found by inspecting the genetic material of every living member of that species or population. A large gene pool indicates extensive genetic diversity, which is associated with robust populations that can survive bouts of intense selection. Meanwhile, low genetic diversity (see inbreeding and population bottlenecks) can cause reduced biological fitness and increase the chance of extinction of that species or population.