It is only by long and laborious study, and by the comparison of a number of individuals, that it will be possible to succeed in establishing correct average proportions each age, and in settling the limits betwixt they can be made to vary, without ceasing to be accurate and faithful to nature—our first and guide in this difficult study.

Preface of M. Quetelet - A Treatise on Man and the Development of His Faculties (1842)