This book reminds us of how much we don't know, not how much we do know about ancient man. Much of the discussion in this book is about "homo habilis" -- meaning "handy man." It is difficult to state with any assurance the age of this man because time frames change routinely with new findings.
Some things we do know. Man had to come out of the trees and become bipedal before he could use tools because his hands had to be free to use tools. Monkeys do use tools to smash things (such as to eat) but they do not create new tool varieties, such as man did. Early man was a scavenger; he ate what was left over after a predator brought the wild animal down. In other words, early man was a great scavenger but, until he socially collaborated with others, he was a mediocre hunter.
Much of the discussion of this book is about the placement of the homo habilis in the scheme of human development. In some ways, homo habilis is a missing link in the evolvement from Australopithecus to homo sapiens. The first important finds of skeletal hominids were in Asia. However, the famous Leakey paleontology family found earlier bones in Africa(they studied in Africa for an incredible 33 years).
Much of what I've learned from this book is to wait -- more findings will create new avenues of discovery about the beginning of man. It is now obvious that various varieties of an early man overlapped by living at the same time (adapting to their environment in differing ways, who then naturally selected those features that would help him adapt more). However, deciding the correct order and relationships between different hominids is dicey.