A survey of sexes and ages in patients attending the Hartlepool diabetic clinic was carried out for the 20-year period 1948-67. The proportion of men aged 50 and over rose from 25.9% in the first decade to 38.2% in the second. An attempt has been made to explain this pronounced and rapid change.

Both males and females of heliothine moths utilize sex-pheromones during the mating process. Females produce and release a sex pheromone for the long-range attraction of males for mating. Production of sex pheromone in females is controlled by the peptide hormone (pheromone biosynthesis activating neuropeptide, PBAN). This review will highlight what is known about the role PBAN plays in control...

Parents divide their reproductive effort into the production of sons and daughters. Darwin (43) was intrigued by the fact that parents usually split their effort so that approximately equal numbers of sons and daughters are raised. He believed that this male : female ratio had been adjusted by natural selection because he understood that the number of females set a limit on reproductive capacit...

In selecting opposite-sex friends (OSFs), men prioritize physical attractiveness, whereas women prioritize physical prowess and economic resources. This parallel with mate preferences suggests mating mechanisms may partially drive OSF preferences. Selection would have favored activation of mating mechanisms when the probabilistic net benefits of pursuing a mating strategy with OSFs exceeded tho...

OBJECTIVE To examine the trends in the proportion of annual live births that were male in Canada and to compare the trends with those in the United States. DESIGN Analysis of census data. SETTING Canada as a whole and 4 main regions (West, Ontario, Quebec and Atlantic). SUBJECTS All live births from 1930 to 1990. OUTCOME MEASURES Sex ratio (expressed as the proportion of total live birt...

The effect of delayed mating on reproductive potential, longevity and oviposition period of female redbanded leafroller, Argyrotaenia velutinana (Walker) and Pandemis leafroller, Pandemis pyrusana Kearfott, was investigated in the laboratory. Virgin female or male moths of each species were held for 1, 2, 4, 6 or 10 days prior to pairing with one-day-old virgin conspecifics of the opposite sex....

Are there other ways of explaining these behaviours? Spiteful behaviours have sometimes also been interpreted as a form of altruism or indirect altruism. Mutually harmful behaviours are favoured if they result in a benefit for some third party that is sufficiently related to the actor. Here, there is no requirement for negative relatedness to one’s victims, and so a distinction has been made be...

The breeding system of parasitic protozoa affects the evolution of drug resistance and virulence, and is relevant to disease diagnosis and the development of chemo- and immunotherapy. A major group of protozoan parasites, the phylum Apicomplexa, that includes the aetiological agents of malaria, toxoplasmosis and coccidiosis, all have dimorphic sexual stages. The sex ratio (proportion of males p...

A recent study comparing sex ratios produced by experimental evolution in spider mites with those predicted by Hamilton's Local Mate Competition Theory clearly demonstrates Evolutionary Theory's success as a quantitatively predictive science.