Along with warm-bloodedness goes evolution of efficient insulation in the form of hair, fur or layer of fat deposits. This was the most efficient mode of reproduction and made the mammals take better care of their offspring. Most important the evolution of intelligent behavior came with mammals. They exhibit curiosity, adaptability, capability of learning from experiencing. The first primates appeared about 65 million years ago- tree mammals.
All primates have large brains, developed eyes and good stereoscopic and binocular vision.
The sight became all important and the tendency to explore and manipulate surroundings with limbs increased. The evolution of the thumb holds greater significance since the ability to grasp tools, climb trees and defend oneself from offensive wild animals originated from it. The capacity of grasping objects by foot is lost in man but the hand remains the grasping tool. The primates later diversified into Prosimians, Monkeys, Apes and Man . The Gibbons, Simians and Orangutans are arboreal but Gorillas and chimpanzees are terrestrial.