Human breasts: Unsupported hypotheses reviewed

Unlike other apes, human females’ breasts develop before first pregnancy and are permanently enlarged. Evidence suggests breasts act as signals to males but the critical data required to confirm this are lacking. These facts have led to a number of hypotheses about the evolutionary and adaptive significance of the human breast which fall into two groups. Those that address the presence of breasts in humans are (a) that they act as releasers of male sexual behaviour, (b) that they enable females to hide their reproductive condition, and (c) that they allow infants to nurse from their mother’s hip. Those that address variability in breast size are (d) that large breasts indicate lactational potential, (e) ability of mothers to invest prenatally in offspring, (f) mother’s fecundity, and (g) her longevity. Each hypothesis is reviewed and evaluated using logical or empirical arguments. Possible ways in which the adaptive significance of human breasts can be determined in contemporary populations are outlined.