I told you how the chimpanzees became biped after the trees virtually disappeared by a natural phenomenon. And how those bipeds were forced to live close together to defend themselves from predators and the elements.
Our predecessors also lived formerly in groups but, however, much further apart.
Living in a group is safer because there are more eyes to discover impending doom in time, one comes by food easier because what the one does not see, the other does, the members learn from the tricks to get something done from each other. In a group you catch prey easier.
One lives there more at ease, although there comes another discomfort instead. Namely the tensions that arise from competition, envy and status enforcement. These, however, count less than the chance to lose your hide or obtaining food easier. One indicates this group life of chimpanzees with a fission-fusion society (there are at the same time separating and binding forces within a group).
This greater compactness due to the disappearance of trees forced them to new behaviour rules. The old rule: "every man for himself" caused in a compactly living group too much "fission".
To survive as a group one had to be more for each other. So altruism purely arose in order to survive and not because one started to be nice and sympathetic for each other autonomously.
In other words: If there was too much zeal and envy within a group then this was doomed to disappear, they didn’t manage protective tasks that were necessary on the ground, they were eaten or perished because of shortcomings.
© Max Farjon 2018