The primate evolution

Primates

The first primitive primates evolved about 53 million years ago (mya). They were small shrew-like insectivores that led an arboreal life (tree dwellers).

Primate life was made possible by the development of limber shoulder joints that enabled the animal to swing (branchiate) easily among the tree branches.

These early primates were especially dextrous with their hands as they had opposable thumbs that closed to meet the fingers, allowing the animal to reach out and bring food or fruit to the mouth. They also had nails instead of claws.

Primate ancestor ( insectivorous squirrel-like)

The eyes were closer together on the front of the face, a development that enabled the animal to have excellent stereoscopic colour vision, the ability to see the world in three dimensions of length, width and depth. The primates could judge the distance and position of adjacent branches. The visual cerebral cortex of the brain was enlarged, as did centres for hearing and touch. They also had very sensitive fingers for feeling.

However, the sense of smell was reduced in preference for the sense of sight. In order to foster learning, the births became mostly single and the period of caring for the young was very much elongated. 
Modern primates consist of two major divisions---the prosimians (premonkeys) and the anthropoids (monkeys, apes and man).

                                   A lemur                                                                 A gibbon

The prosimians are more or less primitive apes that comprise the lemurs, aye-ayes, lorises, pottos and galogos. The lemurs and aye-ayes are found only on the island of Madagascar, off the East African coast. The lorises, pottos and galogos are found in South Eastern Asia and tropical Africa.

Lemurs are small arboreal creatures with hairy bodies and long tails. They have opposable thumbs. Some digits have nails while others have claws. The tarsier is a more advanced prosimian than the lemur and is found in the Philippines and South East Asia. It is mainly arboreal.

Anthropoids

Included among the anthropoids are the New World monkeys, the Old World monkeys, the gibbons and the hominids (apes and humans). The New World monkeys and the Old World monkeys differ in many ways. The Old World monkeys are found in the continents of Africa and Asia, while the New World monkeys are found primarily in the South and Central America.

                                    Old world monkeys (baboon)                       New World monkey (golden lion tamarin)

The New World monkeys have a prehensile tail, used in grasping branches, which is not present in the Old World monkeys. The New World monkeys have flat, widely separated nostrils that open to the side. Those of the Old World monkeys are not only protruding and close together, they face forwards and downwards. The New World monkeys lack ischial callosities or seat pads, which are coloured areas on their buttocks characteristic of the Old World monkeys such as the baboons.

The gibbons are the smallest apes and weigh between 5^1/₂ kg to 10 kg. They are found in South East Asia. They have very long arms that reach the ground even when the animal is standing. They are adapted for swinging from branch to branch. The gibbons are excellent acrobats and spend most of their time in trees.

Emergence of the Hominids

Hominids include apes and humans. The apes (Pongidae) consist of the orang-utans, gorillas, bonobos (pygmy chimpanzees) and chimpanzees. Apes are large animals with no tails. When on the ground, they tend to walk semi-erect. They have long arms and bigger brains than other mammals.

 
              An orangutan 

Orang-utans live in the islands of Sumatra and Borneo in Indonesia. The males weigh about 75 kg and spend most of their time on trees.

Gorillas are the largest of the group weighing up to 200 kg and stand two metres tall. They are mainly ground dwellers and are not aggressive animals. Chimpanzees are native to Africa. They are the most human–like of the apes and are quite intelligent. They can be trained to perform simple tasks.

                        A gorilla                                                            A chimpanzee using a tool to get ants 

Biochemical studies
The closeness of animal to one another can be determined by studying the similarities in their DNA nucleotide sequences and the types of proteins they share. Related animals will have greater similarities in their DNA and proteins. The same can also be used to determine their common descent. The closer are two species taxonomically the greater the percentage of the DNA and proteins they share.

Studies of this nature show that bonobos, gorillas and chimpanzees are the closest ancestors of humans, being genetically 98.5 % identical to man. From this, it is estimated that separation from a common ancestral stock probably occurred around 8 to 5.5 mya. By 4.4 millions years ago, man had separated from the primates

The gibbon has the least similarity to humans and appears to have taken a different evolutionary line from the rest of the apes over 18 mya followed by the orang-utan 6 million years later.
From Ape to Human

The change from ape to human required a modification of the posture from a sloping one to an upright posture and the abandonment of an arboreal life in favour of a ground one. To accomplish this required modifying the structure of the skeleton. Hence, the long forward tilting pelvic girdle of apes changed to a short and upright one. There was also a reduction in the size of arms because there was no longer any need for branchiation. The foramen magnum, which in apes is well to the rear of the skull, making the head hang forwards, moved to the centre of the skull. The spine assumed an S-curve as opposed to that of apes, which is bow-like.

                                                          From ape to human

Additional morphological changes included a reduction in the sizes of the jaws and teeth while the skull and the brain became larger. The eyebrows became less prominent but the nose became more prominent. In line with bipedalism, the feet became more flattened while the big toe became non-opposable.

First Hominids (human-like creatures)

The Dryopithecus, one of the apes whose fossils have been found in East Africa, China, India and Europe appeared about 35 mya. These dryopithecines appear to have been the first hominids. Unfortunately, their fossil record is sparse, consisting mainly of jaws and teeth.

Fossils representing the first hominids (humans) from East Africa date between 5.6 to 5.8 mya. One fossil that belongs to a creature called Ardipithecus ramidus found in Ethiopia is 4.4 mya. The Ardipithecus looked like a modern chimpanzee but smaller in size. In addition, it was bipedal like modern man. The Ardipithecus belongs to the Australopithecine (southern apes) whose territory extended from Ethiopia to South Africa in the East and westward to Chad between 4.2 to 5. 8 mya.

The Australopithecus whose fossil was discovered in South Africa in 1924 followed the Dryopithecus. It seemed to have  belonged to a  young human creature named Australopithecus africanus (Southern ape-man) which probably lived about 3 mya. The Australopithecus had an upright gait and walked fully erect. It had human-like teeth and a brain capacity of 300 cc to 600 cc, about one-third that of modern humans. The eye-borrow ridge was more prominent and the face was flatter than that of apes. The pelvic girdle was shorter than that of apes.

Another fossil named Australopithecus afarensis was discovered in Ethiopia in 1974. Lucy, as this fossil was named, had a brain capacity of 500 cc and was fully erect. Lucy lived about 2.9 mya.

                                           In life, Australopithecus may have looked like this

Another creature, Homo habilis or ‘handy man’ seems to have lived about 2 mya and had a brain capacity of 600 cc. We see the beginnings of tool making with Homo habilis. He lived on hunting and gathering fruit. He was given the name “Homo” because of its tool making abilities.

For about one million years, Homo habilis and the Australopithecus coexisted. This has led some people to believe that Homo habilis was probably another Australopithecus. No one really knows if the two were one or two different creatures.

                                                               Brain size

Homo erectus who seems to have evolved from Homo habilis lived from about 1.5 million to 300,000 years ago. Homo erectus, (erect man) had a brain capacity of 750 cc to 1300 cc, almost similar to that of modern man of 1000 cc to 1700 cc. Homo erectus lived in huts, caves and built fires. He wore animal skins and made elaborate tools. He hunted game and gathered fruits. He was also intelligent and sociable.

                                                                          Home erectus

 The Neanderthal man, whose remains were originally discovered in the Neander Valley in Germany, replaced Homo erectus. The Neanderthals lived from about 130,000 to 30,000 years ago. They made their tools, performed ritual ceremonies connected with the dead, such as burials, and probably had religious beliefs of some sort.

The Neanderthals had a protruding forehead, with no chin and a flattened skull. The brain capacity was similar to ours.

Modern humans appear about 40,000 years ago with a cranial capacity of 1500 cc. These were the Cro-Magnon men, named Homo sapiens. It is not clear what happened to the Neanderthals. Whether they were killed by the more intelligent Homo sapiens or were absorbed through interbreeding no one really knows.

The Cro-Magnon was a  great hunter, hunting in bands and may have been responsible for the extinction of some animal species. They were quite intelligent and developed a language for communication. Men hunted while the women looked after the children.

About 15,000 years ago they embarked on agricultural activities. Dependable food supply made towns and cities possible and the population increased. From an agricultural revolution emerged an industrial revolution.