If we want to ape the developmental line to follow, we must first try to know something about the locomotion of primates. After the first clue to the hominid evolution could be found using the different ways in which primates in trees move.

Ratlike insectivores
Around 75 million years ago called ratlike small insectivores from the ground in the trees. They moved about in the way of current squirrels. But among those copies of this group of animals, that would change in primates, a relatively rapid evolution took place. To them with claws for hands, fingers, suitable for them to intervene. Some groups developed a method of locomotion, which was based on a slow but sure 'four hands' movement. A movement that was marked by an iron grip, the power was out of all proportion to the size of the animal. Potto's still moving this way, the plump and lories. Both groups have strong hands.

The potto
This animal is an African ape with a woolly coat. He is the most active at night. Very slowly and deliberately scrambles the potto along branches. He is very strong for his size and has a grip like a vise. The thumb is very mobile and on each foot, he has a "toilet nail" to account for the care. All other nails have become flat.

Jumping and sticking
Another way of moving towards was jumping and sticking. Some early prosimians were very good jumpers. They had long legs (in proportion as long as those of kangaroos) and very short arms. Most were very small. Some of the species are still surviving. The tarsier Philppijnen the example is not bigger than a kitten, a kitten.

The Tarsier
The Tarsier is an ape and one of the first primates evolved from a creature that closely resembled today's tree shrew. Ghost Animals are now only in Southeast Asia. They are small nocturnal insects and lizards eat. They have oversized, kangaroo-like hind legs and four hands "to join action. They are leaping forward and grabbing.

Tree shrew's
The tree shrew's now in Southeast Asia, very similar to the small, insectivorous, ratlike animals that are considered the ancestors of all primates. They are real beasts, with claws on their feet instead of the flat nails of the other, more evolved primates.

Number prosimians greater in length
Over time, a larger number of lemurs. It was never clear why exactly happened. We only know that in all species, forces were at work influencing the selection of larger individuals promoted, where no small advantage. The benefits of greater length:
larger, more aggressive males have a smaller point in the battle for females;
a larger format, one animal (like the small ape) protect against attacks from some small snakes and birds of prey that are not strong enough to catch larger prey.

Note
In fact, a snake or bird of prey evolution of larger animals in a group may stimulate a disproportionate number of smaller fish to kill them and thus eliminating from the reproductive material.

Optimum size
Increasing size may entail difficulties. It is not easy to hide a big body. Less easily than at least one small body. A large body also needs more food. If the food consists of fruit, soft leaves and shoots at the ends of branches, then at some point the advantage of greater no longer outweigh the disadvantage of inaccessibility of the ends of the branches, where the best food found.

In short:
There is an optimum size for each livelihood. When the pressure behind the selection of a larger size is strong enough, the way of living is changing. A jumper can grab one, with longer arms.

Appearance of large primates
Under above mentioned influences started in the Oligocene (about 40 million years ago), larger, heavier, easier primates with long arms to appear. The choice of food began to change. Accordingly, they chose different parts of the same tree. Some of these primates were Langarm quadrupeds and moved easily along the branches on all four of their legs. These primates were the monkeys. Other (with even longer arms) developed more in the direction of reaching, climbing, hanging and swinging. Those were the great apes.