Question about evolution?

Humans do not have fangs or claws in which to protect themselves the way other animals do. They have hands which came from the ape family which have them to climb trees for protection. We started walking upright when we left the trees. Here is the problem, they should have died off because their protection was the trees. Something unusual had to happen, so that they survived this time period, before walking upright, which made running with a baby possible. They had help of some kind.