Mostly quoting from the book:
“Fifty-five million or so years ago, primitive mammals were of two main sorts. One, rodent-like, remained on the ground; the other took to the trees. In this way the competition of the two families for resources was lessened and strains of each survived to people the world with the creatures we know today. The second group were the prosimians. We are among their descendants, for they were the ancestors of the first primates.”
in of the first primates were already much more complex than those of any of their predecessors; they were bigger, too. Somewhere the brain of one or more of these strains became complex enough and its physical powers sufficiently developed for the animal to cross the line at which the world as a mass of undifferentiated sensations becomes at least in part a world of objects. Whenever this happened it was a decisive step towards mastering the world by using it, instead of reacting automatically to it.”
This is quite interesting as this is what differentiates humans from others. Apparently most animals are genetically programmed to behave is a certain way. There is little deviation from that behavior. We modify our behavior based on knowledge and experience.
“The evidence is fragmentary, but suggests that some fifteen or sixteen million years ago a very successful species was wide spread throughout Africa, Europe and Asia. Probably it was a tree-dweller and certainly specimens were not very large – they may have weighed about 40 pounds”
“… some kind of fork in the road of primate evolution had occurred. While one branch was to lead to the great apes and chimpanzees, the other led to human beings. This line has been named ‘hominid‘.”
ikipedia.org/wiki/Homo_habilis”>Homo habilis is the first species identified with tool-using. Quite likely, we are direct descendants of Homo habilis.
An interesting point is that human children need care long after birth. Not many other species show this behavior. The link of this behaviour with missing oestrus is well derived.
“It may be with the offspring of Homo erectus that there began that long extension of the period of immaturity whole latest manifestation is the maintenance of young people by society during long periods of higher education.”
“Man is the only animal in which the mechanism of oestrus has entirely disappeared. It is easy to see the evolutionary connexion between this and the prolongation of infancy: if female hominids had undergone the violent disruption of their ordinary routine which the oestrus imposes, their offsprings would have been periodically exposed to a neglect which would have made their survival impossible.”