All objects have a gravitational attraction to each other. This is called gravity. The attraction is proportional to the mass of the objects. The attraction is inversely proportional to the distance between the objects
Primates are remarkably the first mammals so when the earth formed about 4.5 billion years ago and the first life on earth dates to 3.5 billion years the primates did not appear before the 50-55 years ago.
Thus by the end of Mesozoic Era i.e about 65.5 million years ago, the primate started to have originated over the earth's surface. At that time the North American continent was still connected to the European landmass and India then was not a part of Asia and most of the landmasses had warm tropical or subtropical climates.
The body size of the early monkeys and apes that took the advantages of vast expanses of land and where the biggest animal to revolve around the 39-40 million years and flourished in the Oligocene Epoch.
