Primates are the highest evolved group of mammals made up of human beings and the animals most closely related to them. Evolution is a gradual process in which something changes into a different and more complex form. The word evolution may refer to various types of change. However, in Biology, the word commonly refers to the formation and development of life on earth.
Primates are remarkably recent animals. It is estimated that the earth is about 4.55 billion years old. The first known primates did not make their appearance until about 60 million years ago. This was around the time of the end of the Mesozoic Era, when the dinosaurs became extinct. Scientists classify primates into two main types. The Prosimians, which include the aye-ayes, lemurs, galagos, lorises,pottos and the tarsiers. The second type is the Anthropoids, which include the monkeys, apes and the human beings. The Anthropoids have more of the characteristic primate features than do the Prosimians. In general, the Anthropoids are also larger. They have larger and more complex brains and are more intelligent than the Prosimians.
The first formed Primates, also known as Proto primates were similar to Tree shrews and squirrels in size and appearance. Fossil evidence tells a lot about their physical appearance and habits. Most of them were adapted to an arboreal way of life. (Tree living animals) They had hands and feet that were equipped with nails rather than claws. The orbits on the skull were placed in such a way, that they must have had forward-looking eyes. This would have facilitated stereoscopic vision, which is a great asset in judging the distance to catch their prey. As the early primates evolved further, their brains and eyes became larger, and the snouts became smaller. This orbital convergence accompanied by olfactory regression indicated that they relied more on their sense of sight rather than their sense of smell in their daily navigation. The increase in the size of the brain was an indication of their rising level of intelligence. One of the main features that distinguished them was the location of the foramen magnum , the hole in the skull through which the spinal cord emerged from the brain. Later fossils showed that this was leading to the erect posture of the head.
There are three main theories of the Origin of the primates.
1. The arboreal theory:This is the oldest theory, and still prevails, with few questions. It simply stated that it was the tree living adaptations that distinguished and lead to the evolution of the primates. These adaptations made them more likely to survive. In order to catch a prey, they needed grasping hands. The hands and an opposable thumb made this possible. Later on, the long swinging tails of the monkeys, called prehensile tails helped them to swing from branches while locating food.
2. The visual predation theory: This lays more emphasis on the stereoscopic vision.
The ability to judge the distance while stalking its prey gave the primates a great advantage. It eliminated the need of the owl like sideward movement to locate an object.
3. The angiosperm radiation theory: This is a much recent theory. According to this,
the radiation of the flowering plants encouraged the radiation evolution of the primates. Most primates were omnivorous and followed their quest for food. There are a number of unanswered questions in this theory, and it needs a lot more supporting evidence. In the meantime, the arboreal and the visual predation theories are accepted.
Almost all primates except human beings live chiefly in tropical and sub tropical climates. Most primates live is social groups, but some Prosimians live alone. Primate infants are much dependent on their mother and learn from their mother.
About 14 million years ago, in the African continent, a group of apes are supposed to have given rise to the first ancestor of the hominid. Today, scientists use many non-human primates for conducting research to learn more about the behavior and diseases of the current day Homo sapiens.