The cheetah is a carnivore, eating mostly mammals under 40 kg (88 lb), including the Thomson's Gazelle, the Grant's gazelle, the springbok and the impala. The young of larger mammals such as wildebeests and zebras are taken at times, and adults too, when the cats hunt in groups. Guineafowl and hares are also prey. While the other big cats mainly hunt by night, the cheetah is a diurnal hunter. It hunts usually either early in the morning or later in the evening when it is not so hot, but there is still enough light. The cheetah hunts by vision rather than by scent. Prey is stalked to within 10–30 m (33–98 ft), then chased. This is usually over in less than a minute, and if the cheetah fails to make a catch quickly, it will give up. The cheetah has an average hunting success rate of around 50% - half of its chases result in failure. Running at speeds up to 112 km/h (70 mph) puts a great deal of strain on the cheetah's body. When sprinting, the cheetah's body temperature becomes so high that it would be deadly to continue - this is why the cheetah is often seen resting after it has caught its prey. If it is a hard chase, it sometimes needs to rest for half an hour or more. The cheetah kills its prey by tripping it during the chase, then biting it on the underside of the throat to suffocate it, for the cheetah is not strong enough to break the necks of the four-legged prey it mainly hunts. The bite may also puncture a vital artery in the neck. Then the cheetah proceeds to devour its catch as quickly as possible before the kill is taken by stronger predators. The diet of a cheetah is dependent upon the area in which it lives. For example, on the East African plains, its preferred prey is the Thomson's Gazelle. This small antelope is shorter than the cheetah (about 58–70 cm (23–28 in) tall and 70–107 cm (28–42 in) long), and also cannot run faster than the cheetah (only up to 80 km/h (50 mph)), which combine to make it an appropriate prey. Cheetahs look for individuals which have strayed some distance from their group, and do not necessarily seek out old or weak ones. More than half of the cheetah cubs are killed by lions, hyenas, and leopards.
The genus name, Acinonyx, means "no-move-claw" in Greek, while the species name, jubatus, means "maned" in Latin, a reference to the mane found in cheetah cubs. The cheetah has unusually low genetic variability and a very low sperm count, which also suffers from low motility and deformed flagellae. Skin grafts between non-related cheetahs illustrate this point in that there is no rejection of the donor skin. It is thought that it went through a prolonged period of inbreeding following a genetic bottleneck during the last ice age. It probably evolved in Africa during the Miocene epoch (26 million to 7.5 million years ago), before migrating to Asia. New research by a team led by Warren Johnson and Stephen O'Brien of the Laboratory of Genomic Diversity (National Cancer Institute in Frederick, Maryland, United States) has recently placed the last common ancestor of all existing cat species as living in Asia 11 million years ago, which may lead to revision and refinement of existing ideas about cheetah evolution. Now-extinct species include: Acinonyx pardinensis (Pliocene epoch), much larger than the modern cheetah and found in Europe, India, and China; Acinonyx intermedius (mid-Pleistocene period), found over the same range. The extinct genus Miracinonyx was extremely cheetah-like, but recent DNA analysis has shown that Miracinonyx inexpectatus, Miracinonyx studeri, and Miracinonyx trumani (early to late Pleistocene epoch), found in North America and called the "North American cheetah" are not true cheetahs, instead being close relatives to the cougar.
For a short time it was thought that there were six subspecies of cheetah, but Acinonyx rex - the king cheetah (see below) - was abandoned after it was discovered the variation was only a recessive gene. The subspecies Acinonyx jubatus guttatus - the woolly cheetah - may also have been a variation due to a recessive gene. Other populations have been elevated to subspecies level, and there are again six subspecies recognized:
- Asiatic Cheetah (Acinonyx jubatus venaticus): northern Africa (Algeria, Djibouti, Egypt, Mali, Mauritania, Morocco, Niger, Tunisia and Western Sahara) and Asia (Afghanistan, India, Iran, Iraq, Israel, Jordan, Oman, Pakistan, Saudi Arabia, Syria, Russia and the Commonwealth of Independent States)
- Northwest African Cheetah (Acinonyx jubatus hecki): western Africa (Benin, Burkina Faso, Ghana, Mali, Mauritania, Niger, and Senegal)
- Acinonyx jubatus raineyii: eastern Africa (Kenya, Somalia, Tanzania, and Uganda)
- Acinonyx jubatus jubatus: southern Africa (Angola, Botswana, Democratic Republic of the Congo, Mozambique, Malawi, South Africa, Tanzania, Zambia, Zimbabwe and Namibia)
- Acinonyx jubatus soemmeringii: central Africa (Cameroon, Chad, Central African Republic, Ethiopia, Nigeria, Niger, and Sudan)
- Acinonyx jubatus velox