The natural inequality of the two powers of population and of production in the earth, and that great law of our nature which must constantly keep their efforts equal, form the great difficulty that to me appears insurmountable in the way to the perfectibility of society.

It is an acknowledged truth in philosophy that a just theory will always be confirmed by experiment.

In 1860, sixty-three per cent of the couples married in Great Britain had families of four or more children; in 1925 only twenty per cent had more than four.

A writer may tell me that he thinks man will ultimately become an ostrich. I cannot properly contradict him.

Population, when unchecked, goes on doubling itself every 25 years or increases in a geometrical ratio.

It does not, however, seem impossible that by an attention to breed, a certain degree of improvement, similar to that among animals, might take place among men. Whether intellect could be communicated may be a matter of doubt: but size, strength, beauty, complexion, and perhaps even longevity are in a degree transmissible... As the human race could not be improved in this way, without condemning all the bad specimens to celibacy, it is not probable, that an attention to breed should ever become general.

The germs of existence contained in this spot of earth, with ample food, and ample room to expand in, would fill millions of worlds in the course of a few thousand years.