The small families, say of two, are born when the parents are both young, and carefully compiled statistics prove that these are not the best offspring a couple can produce.

Those born first in wedlock, are shorter and not so well developed as those born later in married life, when parents are more matured.
If it is substantially true, that the decline in the birth-rate is due to voluntary prevention, and that prevention implies prudence and self-control, it is safe to conclude that those in whom these qualities are absent or least conspicuous, will be the most prolific.
But those in whom these qualities are absent or least conspicuous are our worst citizens, and, therefore, our worst citizens are the most prolific.

Observation and statistics lead to the same conclusion.
Amongst the very poor in crowded localities, the passion for marriage early asserts itself.
Its natural enemies are prudence and a consciousness of responsibility, and these suggest restraint.

But prudence and restraint are not the common attributes of the very poor.

Poverty makes people reckless, they live from hour to hour as the lower animals do.