The chapter discusses the evolution of sexual selection in males and females, highlighting the complexity and diversity of mechanisms involved. Darwin's theory of sexual selection, which posits that elaborate traits in males are driven by intrasexual competition for breeding opportunities or attracting mates, has been refined and expanded upon. Recent studies have shown that female sexual selection is also significant, with intense competition among females for resources and breeding opportunities leading to the development of secondary sexual characters in females. These characters can include physical ornaments, aggressive displays, and changes in behavior. The chapter emphasizes that the operation of sexual selection in females is more complex than previously thought, involving both intrasexual competition and male mate choice. It also notes that the costs and benefits of these traits can vary between sexes, and that the evolution of sex differences in behavior and morphology is influenced by a combination of selection pressures and resource distribution. The chapter concludes by calling for further research to better understand the mechanisms and implications of sexual selection in females.The chapter discusses the evolution of sexual selection in males and females, highlighting the complexity and diversity of mechanisms involved. Darwin's theory of sexual selection, which posits that elaborate traits in males are driven by intrasexual competition for breeding opportunities or attracting mates, has been refined and expanded upon. Recent studies have shown that female sexual selection is also significant, with intense competition among females for resources and breeding opportunities leading to the development of secondary sexual characters in females. These characters can include physical ornaments, aggressive displays, and changes in behavior. The chapter emphasizes that the operation of sexual selection in females is more complex than previously thought, involving both intrasexual competition and male mate choice. It also notes that the costs and benefits of these traits can vary between sexes, and that the evolution of sex differences in behavior and morphology is influenced by a combination of selection pressures and resource distribution. The chapter concludes by calling for further research to better understand the mechanisms and implications of sexual selection in females.