THE BASIS OF THE POPULATION PROBLEM: (1) THE QUANTITATIVE
ASPECT 37
(1) The ancestors of man were once subject to the conditions
prevailing among species in a state of nature. These conditions
are studied. (2) Reproduction, the necessity for which can be
explained, (3) always consists in the fusion of two gametes, but
(4) is accomplished by different methods. (5) Whatever the
method, most ripe ova are fertilized, though among lower forms
failures may not be infrequent. A reference to the nature of (6)
reflex action, (7) instinct, (8) intelligence, and (9) reason
shows that, (10) whatever the stage of mental evolution reached
among species in a state of nature, reproduction is essentially
‘mechanical’. (11) The vast number of ova (12) is only partially
called for by the fact that a certain proportion only is
fertilized. The vast number is necessary because (13) owing to
the interdependence of all species a large proportion of the
young of (14) both animals (15) and plants perish before
maturity (16) and is determined by the sum of the dangers to
which the young are exposed.