The Trivers Willard Hypothesis predicts that under certain
conditions, individuals will bias their investment in offspring
differently depending on the sex of the offspring. It is
believed that this can be as extreme as infanticide or as subtle
as providing different amounts of breast milk. A new study by
Katherine HInde finds that macaques may do this. However, I
think this may be counterintuitive. Hinde uses data from 106
rhesus macaques (Macaca mulatta) to show that first time mothers
produce richer milk when they have sons compared to when they
have daughters. She suggests that “[t]his difference seems to
reflect the tradeoffs between the benefits derived from
additional investment in sons and the costs of diverting energy
from maternal growth and development.” The reason that I say
that this is counterintuitive is this: Previous studies on
female bonded primates have shown relatively little bias in
investment … Boyd and Silk showed this to be, essentially, a
random relationship so while some studies show