Intra-sexual selection in Drosophila is a form of sexual selection where competition between members of one sex for mates occurs. This process is primarily observed in males, leading to increased variability in their fertility compared to females. The study by Bateman shows that in Drosophila melanogaster, males contribute more variably to the next generation than females, indicating stronger intra-sexual selection in males. This is due to the greater dependence of male fertility on the frequency of insemination. The results suggest that intra-sexual selection is a result of the primary sexual differentiation, where males produce more gametes than females, leading to competition among male gametes for fertilization of female gametes. This competition is more intense than previously thought. The study also shows that females are more discriminating in their mating choices, which is consistent with the idea that intra-sexual selection is mainly driven by male competition. The experiments used dominant marker genes to track mating behavior and fertility, revealing that males have a higher variance in the number of mates and fertility. This supports the idea that intra-sexual selection is more pronounced in males. The findings indicate that the sex difference in fertility variance is due to the number of mates per fly affecting fertility, with males showing a stronger correlation between number of mates and fertility. This highlights the role of intra-masculine selection in shaping sexual behavior and reproductive strategies in Drosophila. The study also discusses the broader implications of intra-sexual selection in sexual reproduction, suggesting that it is a fundamental aspect of sexual differentiation in both animals and plants. The results provide insights into the evolutionary mechanisms underlying sexual selection and the factors influencing mating behavior and fertility in different species.Intra-sexual selection in Drosophila is a form of sexual selection where competition between members of one sex for mates occurs. This process is primarily observed in males, leading to increased variability in their fertility compared to females. The study by Bateman shows that in Drosophila melanogaster, males contribute more variably to the next generation than females, indicating stronger intra-sexual selection in males. This is due to the greater dependence of male fertility on the frequency of insemination. The results suggest that intra-sexual selection is a result of the primary sexual differentiation, where males produce more gametes than females, leading to competition among male gametes for fertilization of female gametes. This competition is more intense than previously thought. The study also shows that females are more discriminating in their mating choices, which is consistent with the idea that intra-sexual selection is mainly driven by male competition. The experiments used dominant marker genes to track mating behavior and fertility, revealing that males have a higher variance in the number of mates and fertility. This supports the idea that intra-sexual selection is more pronounced in males. The findings indicate that the sex difference in fertility variance is due to the number of mates per fly affecting fertility, with males showing a stronger correlation between number of mates and fertility. This highlights the role of intra-masculine selection in shaping sexual behavior and reproductive strategies in Drosophila. The study also discusses the broader implications of intra-sexual selection in sexual reproduction, suggesting that it is a fundamental aspect of sexual differentiation in both animals and plants. The results provide insights into the evolutionary mechanisms underlying sexual selection and the factors influencing mating behavior and fertility in different species.