The article by A. J. Bate-man explores the concept of intra-sexual selection in Drosophila, a species where mating is promiscuous and the sexes are numerically equal. The author discusses the historical context of sexual selection, highlighting Huxley's criticisms of Darwin's original concept, which emphasized competition for mates. Huxley introduced the term "epigamic" to describe traits that increase fertility and have selective value for the species, while "intra-sexual selection" refers to competition between males for mates, often indirectly affecting species survival. Bate-man's experiments focus on the intensity of selection, measured by the variance in fertility, which is a measure of the intensity of selection. The results show that the variance in fertility is higher in males than in females, indicating greater intra-masculine selection. This is attributed to the higher variance in the number of mates per male and the stronger correlation between the number of mates and fertility in males. The author suggests that the primary cause of intra-masculine selection is the greater dependence of males on the frequency of insemination for their fertility, which is a universal attribute of sexual reproduction. The article also discusses the implications of intra-masculine selection, such as the tendency for males to show polygamous behavior and the potential for epigamic traits to have different selective values in males and females. The author concludes that the widespread distribution of intra-masculine selection is linked to the XY mechanism of sex determination, where males are usually the heterogametic sex, suggesting a selective advantage for heterogametic males.The article by A. J. Bate-man explores the concept of intra-sexual selection in Drosophila, a species where mating is promiscuous and the sexes are numerically equal. The author discusses the historical context of sexual selection, highlighting Huxley's criticisms of Darwin's original concept, which emphasized competition for mates. Huxley introduced the term "epigamic" to describe traits that increase fertility and have selective value for the species, while "intra-sexual selection" refers to competition between males for mates, often indirectly affecting species survival. Bate-man's experiments focus on the intensity of selection, measured by the variance in fertility, which is a measure of the intensity of selection. The results show that the variance in fertility is higher in males than in females, indicating greater intra-masculine selection. This is attributed to the higher variance in the number of mates per male and the stronger correlation between the number of mates and fertility in males. The author suggests that the primary cause of intra-masculine selection is the greater dependence of males on the frequency of insemination for their fertility, which is a universal attribute of sexual reproduction. The article also discusses the implications of intra-masculine selection, such as the tendency for males to show polygamous behavior and the potential for epigamic traits to have different selective values in males and females. The author concludes that the widespread distribution of intra-masculine selection is linked to the XY mechanism of sex determination, where males are usually the heterogametic sex, suggesting a selective advantage for heterogametic males.