THE ‘LAWS’ OF BIOLOGICAL GROWTH

Abstract

THE study of mere increase in size and weight has steadily lost the interest of British students of growth since D'Arcy Thompson¹ and later Huxley² directed their research to other fields. Many of the beliefs about organic growth that formerly seemed reasonable or even self–evident—in the existence, for example, of an integral biochemical process known as ‘growth metabolism’–have now been refuted or superceded; and it is only quite recently that students of growth have stopped applying to the organism the fiscal concept of interest, or increments of size, accumulating at finite intervals. Minot³ always used it. The inspection of curves of growth has nevertheless made known a number of general principles concerning the dependence of the size of organisms on their age which it is very worth while to collate and comment upon. These laws are of the growth of individual organisms. It was Davenport⁴ who first pointed out the unsuspected extent to which curves of growth compiled from mass statistics may be corrupted by what are in reality curves of distribution. At puberty, for example, the growth of individual boys shows a marked spurt, the time of onset of which in the male population as a whole is normally distributed about a mean value at approximately 14½ years. The ‘adolescent growth component’ of the mass curve of human growth, to which Robertson6 fitted his well–known ‘monomolecular autocatalytic’ function, does not occur in the curve of individual growth. Davenport showed that it was essentially a modified Gaussian curve of error, indicating the distribution in time of the onset of adolescent growth spurts.