Genetic Variation In the Cheetah

To find out if cheetahs showed a lack of genetic variation, O'Brien tested blood samples from 55 of the cats, comparing 52 different proteins found in the blood of each animal. Genes carry the instructions for building proteins, and any slight variation in the makeup of a protein reflects a corresponding variation in a gene. O'Brien found that for nearly all the proteins he tested, the cheetahs in his study had virtually the same genetic makeup. His tests showed that cheetahs may be as similar genetically as mice that scientists have deliberately inbred—by mating cousins, siblings, and other close relatives for many generations—to create uniform strains of mice for use in laboratory experiments.

But most of the cheetahs in O'Brien's study had been out of the wild only a generation or two at most, so their genetic uniformity was not the result of inbreeding by zoos. How, then, did cheetahs become so similar?

O'Brien speculated that in the distant past, the cheetah population experienced one or more bottlenecks—drastic population crashes in which a large proportion of the species died, leaving, perhaps, only a handful of survivors. Using the cheetah's current degree of variability as a guide, O'Brien calculated that the cheetah probably fell to the brink of extinction beginning 12,000 to 10,000 years ago, at the end of the Pleistocene Ice Age, a period in which many other mammals, such as mammoths and saber-toothed cats, became extinct. According to this view, each of the cheetah's population bottlenecks was followed by extreme inbreeding among the few survivors, which in a drastic case may have numbered only a few litters. This inbreeding, continued over many generations, would have eventually produced a population in which nearly all individuals shared the same limited pool of genes.