An interesting feature that multiple sclerosis (MS) shares with many other immune-mediated diseases is that susceptibility is higher in females than males. 1,2 However, the female-to-male ratio (sex ratio) of MS appears to vary significantly in time and space. A recent meta-analysis of epidemiological studies has shown that the worldwide sex ratio of MS has been substantially increasing over th...

A review of published reports showed that the sex ratio (proportion of boys) was low among infants conceived after ovulation had been induced. The difference between the observed sex ratio and an expected one of 0 . 514 was highly significant. These findings suggest that maternal gonadotrophin concentrations at the time of conception directly affect the sex of the zygote.

tends to have a predictable effect on smoking cessation. However, from a social perspective, it is fairly certain (to within relatively narrow confidence limits) how many cases of lung cancer or cardiac events will be avoided if 10000 persons stop smoking. What this illustrates is that social benefit is more certain than individual benefit. In other words, if we are concerned with a social pers...

Within the area of sex allocation, one of the topics that has attracted a lot of attention is the sex ratio problem. Fisher (1930) proposed that equal numbers of males and females have been promoted by natural selection and it has an adaptive significance. But the empirical success of Fisher's theory remains doubtful because a sex ratio of 0.50 is also expected from the chromosomal mechanism of...

The significance of migration load in driving the evolution of recipient populations has long been documented in population genetics, but its effects have not been linked to the formation of biased sex ratios in natural populations. In this study, we develop a single-locus model to demonstrate how the migration load can shape the primary and secondary sex ratios in dioecious plants where sexual...

Hamilton's "haplodiploidy hypothesis" holds that inflated sororal relatedness has promoted altruistic sib rearing in haplodiploids, potentially explaining their apparent predisposition to eusociality. Here, we suggest that haplodiploidy may instead promote eusociality simply by facilitating sex-ratio adjustment. Specifically, haplodiploidy may enable sex-ratio bias toward the more helpful sex, ...

To our knowledge, there is, so far, no evidence that incubation temperature can affect sex ratios in birds, although this is common in reptiles. Here, we show that incubation temperature does affect sex ratios in megapodes, which are exceptional among birds because they use environmental heat sources for incubation. In the Australian brush-turkey Alectura lathami, a mound-building megapode, mor...

There is much interest in understanding how population demography impacts upon social evolution. Here, we consider the impact of rate and pattern of dispersal upon a classic social evolutionary trait--the sex ratio. We recover existing analytical results for individual dispersal, and we extend these to allow for budding dispersal. In particular, while a cancelling of relatedness and kin competi...

Spiders that live in large cooperative societies are scattered among several taxonomic groups. All quasisocial species appear to have female-biased sex ratios, while congeneric species with less advanced forms of sociality have 1:1 sex ratios. I present two sex-ratio models that examine the interaction between the genetic structure of populations and two aspects of colony demography-the changes...