Thomson parallels and compares competition in the natural world, where the weakest are eliminated and education through play prepares the individual for their environment, with that in the human world, where co-operation protects the unfit and education contributes to a differential birth rate.

He discusses possible reasons for the connection between intelligence, education, and family size, exploring whether this phenomenon is due to genetics, environment, or both. He refers to intelligence testing he has conducted throughout several counties in England, including that of an English mining community and a concurrent test on Fatherless children; and testing carried out by the Mental Defective Committee establishing an increase in the incidence of mental defect.

Thomson outlines the ethical implications of such findings, and how imperative it is that all individuals be offered the best free education they can use. He argues that education is a crucial part of the solution to the differential birth rate.