Growth and Development of Social Groups 
the virtual universality of severe head wounds in Homo erectus 
skulls, including those of both sexes. 
By analogy with the behaviour of other primates and indeed 
of many animal species, and through the recent work done on 
instinctive behaviour in other animals and man7, we now know 
that human beings really are born with built-in drives, although 
some are unco-ordinated. For example, like us, chimpanzees 
have to be taught how to copulate. 
As human beings became increasingly competent in techno- 
logy, so that everyone did not need to seek food from dawn to 
dusk, a division of labour arose between persons of different 
ages and both sexes and eventually between grown men spe- 
cialized in different skills. Out of these specializations grew 
institutions beyond the scope of the family. The chief and his 
followers became a political institution, the knapper of fine 
flints and his clients an economic institution, and so on. 
But the number of kinds of institutions is limited, because 
those that arose in this fashion seem to have followed the lines 
of instinctive motivations. The family is based primarily on sex 
and care of the young; the economic institution on hunger, 
thirst, and the need for shelter; the political institution on the 
demarcation and defence of territories; the religious institution 
on curiosity, fear and deprivation of interaction; and voluntary 
associations on the so-called peck order. Each kind of institution 
has its characteristic patterns of interaction both between its 
members and with outsiders. 
ENERGY CONSUMPTION AND INSTITUTIONAL COMPLEXITY 
The complexity of institutions in a society is a function, 
other things being equal, of man’s conversion of energy into 
social structure. He has done this through the progressive use 
of energy, in technological procedures®. The sequence starts 
with the use of fire and culminates with that of atomic energy, 
and will lead to the use of other kinds of energy known only to 
God and the physicists. Technology in the sense used here is 
not limited to economic institutions but permeates all others. 
Families use dishwashers, presidents fly in private airplanes, 
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