brings inbreeding depression.
Cousins should not mate.
Inbreeding (mating between relatives) results in offspring having reduced fitness. This is known as inbreeding depression and is primarily caused by increased homozygosity at loci with harmful recessive alleles. Small populations, where most or all mates are relatively closely related, are particularly vulnerable to inbreeding and inbreeding depression. The effects of inbreeding depression in small populations can accumulate to reduce the population growth rate and increase the probability of extinction (Keller and Waller 2002).
Despite being of interest since Darwin, inbreeding depression remains a crucial area of research in conservation biology, ecology, and evolutionary biology. As global change, habitat destruction, and fragmentation rapidly progress, many natural populations will become smaller and more isolated and consequently more affected by inbreeding depression.
Original Research: Keller, L. F., and D. M. Waller. 2002. Inbreeding effects in wild populations. Trends in Ecology & Evolution 17:230-241. http://dx.doi.org/10.1016/S0169-5347(02)02489-8
Fred W. Allendorf is Regents Professor of Biology Emeritus at the University of Montana. His primary scientific interest is the application of population genetics to conservation biology. He is senior author of the book Conservation and the Genetics of Populations.