Chapter V: Human Fecundity 88

(1) We have to ask whether human fecundity has changed and what
the effect of certain customs is upon fecundity. (2) It is not
to factors influencing the male (3) but to factors influencing
the female that we have to look. (4) The length of the mature
period increases with good conditions; (5) the interval between
births has decreased in mankind, (6) while the number at a birth
has probably increased (7) owing to good conditions. (8) That
human fecundity has increased is supported by other evidence,
(9) including the number of children, and (10) was held by
Darwin and others. (11) Polygamy has had no influence, but
lactation, age at marriage, early intercourse, and development
of fat adversely affect fecundity. (12) Calculations of possible
increase.