The answer to whether cheetahs are inbred is a definitive yes, making them one of the most genetically uniform species of mammal studied today. This extreme lack of variation is not the result of recent mating choices, but rather a deep-seated biological characteristic that has shaped the species for millennia. The consequences of this genetic uniformity reach into nearly every aspect of the cheetah’s biology, affecting everything from their ability to fight disease to their capacity to reproduce.
Measuring Genetic Uniformity
The extreme genetic similarity of the cheetah was first scientifically established through surprising laboratory evidence, demonstrating a level of uniformity usually only seen between identical twins. One of the most powerful proofs involved performing skin grafts between unrelated individuals taken from different populations. In most mammals, a skin graft from an unrelated donor is quickly recognized as foreign by the recipient’s immune system and is rapidly rejected within days or weeks. However, when researchers exchanged skin grafts between unrelated cheetahs, the grafts were accepted and healed successfully, as if the donor and recipient were the same animal. This acceptance indicated a near-complete lack of variation in the Major Histocompatibility Complex (MHC), the group of genes responsible for immune system recognition and rejection of foreign tissue.
The cheetah’s genetic variation is estimated to be only between 0.1% and 4% of the diversity typically found in other living species. Further molecular studies quantified this profound genetic poverty by measuring heterozygosity, which is the presence of different gene versions at a particular site on a chromosome. Cheetahs exhibit extremely low average heterozygosity, estimated to be around 0.0004 to 0.014, making them the least genetically variable of all known cat species. This low level of genetic variation is less than that of other genetically challenged animals, including the Tasmanian devil and highly inbred domestic dog and cat breeds.
The Historical Events That Caused Low Diversity
The current genetic state of the cheetah is a long-term consequence of historical events that drastically reduced the population to a handful of survivors. This phenomenon is known as a population bottleneck, where a sharp, temporary reduction in population size causes a severe loss of genetic diversity. Scientists hypothesize that the cheetah has endured at least two major bottlenecks in its evolutionary history.
The first and most severe bottleneck is believed to have occurred during the Late Pleistocene epoch, approximately 10,000 to 12,000 years ago, coinciding with a mass extinction event of large mammals. This cataclysmic event wiped out most of the cheetah population, leaving behind a small, surviving group with only a fraction of the species’ original genetic material. For millennia afterward, the descendants of these few survivors interbred, which fixed the low genetic diversity into the species’ genome. A second, more recent population contraction also occurred, driven by human activities and habitat loss, further compounding the genetic issue. In the modern era, the population has continued to decline due to conflict with humans and shrinking ranges, which maintains a low effective breeding population.
Health and Reproductive Impacts of Inbreeding
The lack of genetic variation has resulted in several distinct biological vulnerabilities for the cheetah population. The uniformity of the MHC genes, which are meant to be highly variable, leaves the entire species susceptible to the same infectious diseases. If a new pathogen evolves to evade the immune response of one cheetah, it is likely to be able to overcome the defenses of almost every other cheetah as well.
A devastating example of this occurred in 1983 when an outbreak of Feline Coronavirus (FeCV) struck a cheetah breeding facility. While the same virus causes low morbidity and mortality in domestic cats, all 45 cheetahs at the facility became infected and symptomatic, with a shocking 60% dying within three years. This high mortality rate demonstrates the profound consequence of having a near-monoculture of immune genes. Reproductive issues are another significant consequence of this extreme inbreeding. Male cheetahs suffer from very poor semen quality, characterized by low sperm concentration and a high incidence of malformed spermatozoa. Studies have found that 70% to 80% of cheetah sperm are structurally abnormal, which greatly compromises fertility. Cheetah cubs also experience high mortality rates, often dying before reaching six months of age, particularly in captive settings, which further hinders the species’ ability to recover its numbers.