Our ancestors in the ages during which our present nervous system became fixed, lived, apparently, in loosely organised family groups, associated for certain occasional purposes, into larger, but still more loosely organised, tribal groups.

No one slept alone, for the more or less monogamic family assembled nightly in a cave or 'lean-to' shelter.

The hunt for food which filled the day was carried on, one supposes, neither in complete solitude nor in constant intercourse.

Even if the female were left at home with the young, the male exchanged some dozen times a day rough greetings with acquaintances, or joined in a common task.

Occasionally, even before the full development of language, excited palavers attended by some hundreds would take place, or opposing tribes would gather for a fight.
It is still extremely difficult for the normal man to endure either much less or much more than this amount of intercourse with his fellows.
However safe they may know themselves to be, most men find it difficult to sleep in an empty house, and would be distressed by anything beyond three days of absolute solitude.