Primates mostly live in trees in tropical forests and feed mainly on fruit, leaves, insects and occasionally meat. They range in size from the tiny mouse lemurs of Madagascar (which weigh only 30 grams) to powerful male lowland gorillas that reach up to 275 kilograms.
Most primates have forward facing eyes and see with binocular vision. They have five digits on their hands and feet (although some groups lack thumbs), flattened nails, a shortened snout, large brains in relation to their body weight and a very long childhood.
Primates can be divided into two main groups: the Prosimians and the Anthropoids. Prosimians are generally small-bodied, solitary, nocturnal creatures that rely strongly on scent. This group includes galagoes, bushbabies, lorises, potos and lemurs. Anthropoids, which include monkeys and apes, are predominantly diurnal, social animals that have larger brains in relation to their body weight than prosimians and can see in colour.
Monkeys are divided into two groups: those from the Neotropics (New World monkeys) and those from Africa and Asia (Old World monkeys). They are distinguished by differences in the shape of their nostrils and features of their skulls. Apes are also divided into two categories: lesser apes or gibbons and the great apes (which make up the Family Hominidae and include orangutans, chimpanzees, gorillas and humans). Our place in this family is supported by the fact that humans share approximately 98% of their DNA with our closest relatives, the Chimpanzee and Bonobo.
During the 1980s it was thought there were around 160 species of primates. This number has now increased to approximately 480. This is mostly due to existing subspecies being recognised as distinct species. Even though there are a diverse range of primates, nearly half are listed as threatened by the IUCN with lemurs being the group most in danger of extinction. The main threats to primates are habitat destruction and hunting, either for bush meat or for the illegal trade in body parts used in traditional medicines.
Around 1.8 to 2 million years ago, ancestral humans (which were unusual primates that were able to occupy open habitats, walk upright on two legs and live on the ground) left Africa and spread beyond the tropics to inhabit temperate and subarctic climates. Today their descendant, Homo sapiens (which is a highly intelligent and social ape species) dominates the planet.