Data for: Five decades of data yield no support for adaptive biasing of offspring sex ratio in wild baboons (Papio cynocephalus)

Over the past 50 years, a wealth of testable, often conflicting,
hypotheses has been generated about the evolution of offspring sex ratio
manipulation by mothers. Several of these hypotheses have received support
in studies of invertebrates and some vertebrate taxa. However, their
success in explaining sex ratios in mammalian taxa, and especially in
primates, has been mixed. Here, we assess the predictions of four
different hypotheses about the evolution of biased offspring sex ratios in
the well-studied baboons of the Amboseli basin in Kenya: the
Trivers-Willard, female rank enhancement, local resource competition, and
local resource enhancement hypotheses. Using the largest sample size ever
analyzed in a primate population (n = 1372 offspring), we test the
predictions of each hypothesis. Overall, we find no support for adaptive
biasing of sex ratios. Offspring sex is not consistently related to
maternal dominance rank or biased towards the dispersing sex, nor it is
predicted by group size, population growth rates, or their interaction
with maternal rank. Because our sample size confers power to detect even
subtle biases in sex ratio, including modulation by environmental
heterogeneity, these results suggest that adaptive biasing of offspring
sex does not occur in this population.