Ireland and New Zealand would be equally pleased could they believe that their low, and still decreasing birth-rate is due to the lessening of the sexual instinct, attendant upon, and resulting from a high and increasing intellectual power and activity.

The fact is, that the sexual instinct is so immeasurably in excess of the maximum power of procreation in the female, that an enormous reduction in sexual power would require to take place before it would have any effect on the number of children born.

The number of children born is controlled by the capacity of the human female to bear children, and one birth in every two years during the child-bearing period of life is about the maximum capacity.

A moderate diminution in the force of the sexual instinct might lead to a decrease in the marriage rate, but it would require a very serious diminution bordering on total extinction of the instinct to exert any serious effect on the fecundity of marriage.

All that can be claimed for this theory of population is, that, reasoning from known physiological analogies, we might expect a weakening of the desire for marriage, coincident with the general development of intellect in the race.

There are as yet no facts to prove that such weakening has taken or is taking place, nor are there facts to prove that population has in any way suffered from this cause.

If such a law obtained, and resulted in a diminished birth-rate, the future of the race would be the gloomiest possible.  An inexorable law would determine that there could be no mental evolution, for the best of the race would cease to propagate their kind.  All who would arrive at this standard of mental growth would become barren.  And against this there could be no remedy.

One of the main contentions of this work is that the best have to a large extent ceased to propagate their kind, but it is not maintained that this is the result of a biological law, over which there is no control.  It can be safely claimed that to Malthus’s three checks to population—­vice, misery, and moral restraint, the demographic phenomena of a century have added no other.  The third check, however, moral restraint, must be held to include all restraint voluntarily placed by men and women on the free and natural exercise of their powers of procreation.

Malthus used the term “moral” in this connection, not so much in relation to the motive for the restraint, but in relation to the result, viz., the limitation of the family.  The “moral restraint” of Malthus meant to him, restraint from marriage only, chiefly because of the inability to support a family.  It implied marriage delayed until there was reasonable hope that the normal family, four in number, could be comfortably supported, continence in the mean time being assumed.  Bonar interpreting Malthus says (p. 53) that impure celibacy falls under the head of “vice,” and not of “moral restraint.”