Chapter IX: The Regulation of Numbers Among Primitive Races 197

(1) The theory of Malthus has long been disproved, and (2) has
been replaced by the modern theory of an optimum density of
population. (3) Territories are strictly defined among hunting
and fishing races, and (4) among primitive agricultural races.
(5) Among all these races there is co-operation in the search
for food. (6) The principle of the optimum number holds good for
all of them, and by the natural selection of customs, practices
restrictive of increase come everywhere into use in the shape of
abstention from intercourse, abortion, and infanticide. (7)
Evidence of these practices is incomplete, (8) but shows that
they are so practised as to keep numbers down to a certain
level, (9) and, though they may be adjusted solely by natural
selection, yet some semi-conscious adjustment may take place.
(10) That adjustment should take place, a certain standard of
skill is necessary on the part of those who set up new families
and is ensured by marriage customs. (11) General conditions of
savage life afford evidence that customs are effective. (12)
There is no correlation between these practices and economic
stages; though evidence is lacking, the presumption is that some
such practices were everywhere in use (13) not only among
primitive but also among prehistoric races, (14) who have moved
slowly away from the conditions prevalent in the intermediate
stage.