The Descent of Man

continued use or disuse of parts. The cohesion
of homologous parts. The variability of multiple
parts. Compensation of growth; but of this
law I have found no good instance in the case
of man. The effects of the mechanical pressure
of one part on another; as of the pelvis on the
cranium of the infant in the womb. Arrests of
development, leading to the diminution or
suppression of parts. The reappearance of longlost
characters through reversion. And lastly,
correlated variation. All these so-called laws
apply equally to man and the lower animals;
and most of them even to plants. It would be
superfluous here to discuss all of them (16. I
have fully discussed these laws in my 'Variation
of Animals and Plants under Domestication,'
vol. ii. chap. xxii. and xxiii. M. J.P. Durand
has lately (1868) published a valuable essay, 'De
l'Influence des Milieux,' etc. He lays much
stress, in the case of plants, on the nature of the
soil.); but several are so important, that they
must be treated at considerable length.