OBJECTIVE Preconception sex selection for nonmedical reasons raises important moral, legal, and social issues. The main concern is based upon the assumption that a widely available service for sex selection will lead to a socially disruptive imbalance of the sexes. For a severe sex ratio distortion to occur, however, at least two conditions have to be met. First, there must be a significant pre...

Recent scholarship has documented an alarming increase in the sex ratio at birth in parts of East Asia, South Asia and the South Caucuses. I argue that parents engage in sex selection because of patrilocal norms that dictate elderly coresidence between parents and sons. Sex ratios and coresidence rates are positively correlated when looking across countries, within countries across districts, a...

Sex ratio imbalances found in Asia are primarily due to the increasing proportions of sons among children in China and India. This gradual demographic masculinization over the last two decades results from the rapid progression in the number of sex-selective abortions aimed at ensuring the birth of male children. While other factors such as female infanticide or excess child mortality have play...

OBJECTIVE Sex-ratio at birth in families with previous girls is worse than those with a boy. Our aim was to prospectively study in a large maternal and child unit sex-ratio against previous birth sex and use of traditional medicines for sex selection. MAIN OUTCOME MEASURES Sex-ratio among mothers in families with a previous girl and in those with a previous boy, prevalence of indigenous medic...

Following the suppression of recombination, gene expression levels decline on the sex-limited chromosome, and this can lead to selection for dosage compensation in the heterogametic sex to rebalance average expression from the X or Z chromosome with average autosomal expression. At the same time, due to their unequal pattern of inheritance in males and females, the sex chromosomes are subject t...

Recent empirical studies suggest that genes involved in speciation are often sex-linked. We derive a general analytic model of reinforcement to study the effects of sex linkage on reinforcement under three forms of selection against hybrids: one-locus, two-locus, and ecological incompatibilities. We show that the pattern of sex linkage can have a large effect on the amount of reinforcement due ...

The Red Queen hypothesis argues that parasites generate selection for genetic mixing (sex and recombination) in their hosts. A number of recent papers have examined this hypothesis using models with haploid hosts. In these haploid models, sex and recombination are selectively equivalent. However, sex and recombination are not equivalent in diploids because selection on sex depends on the conseq...

Abstract The year 2021 marks the 150th anniversary of publication Charles Darwin’s extraordinary book Descent Man and Selection in Relation to Sex. Here, we review history impact a single profound insight from Man: that, some few species, females rather than males compete for access mates. In other words, these species are ‘sex-role reversed’ with respect mating competition sexual selection com...