Darwin's appeal to sexual selection in his Descent of Man was motivated by the need to explain traits not obviously of survival value – sexually dimorphic and ornamental traits. After Darwin, there was little interest in sexual selection until the 1970s. Since then there has been much progress due to first, what we now know about sexual reproduction and human evolution in general; second, theoretical developments related to runaway processes, parental investment, mating systems and sexual conflicts and cooperation; third, new empirical data about actual mating preferences in humans and closely related species. Three issues have motivated the debates about sexual selection: the explanatory scope of sexual selection; the nature and existence of sexual selection; the relation between natural survival selection and sexual selection. One recent approach combines survival and sexual selection in the idea that many distinctively human capacities and behaviour are the products of sexual selection on fitness indicators.

Key Concepts:

• The explanatory scope of a theory or hypothesis is the range of phenomena it can potentially explain.
  
• Human fitness indicators are those traits that are possible only in highly fit individuals, and are therefore indicative of high fitness.
  
• Parental investment is the amount of resources a parent devotes to the production and care of offspring, in development from the generation of gametes to birth, and to the feeding, education and support of offspring.
  
• Sexual selection is a result of the struggle to reproduce, and is to be distinguished from natural selection and the struggle to survive.
  
• Surplus abilities in humans are those abilities not obviously explainable in terms of natural survival selection and advantages for survival, such as we see in advanced mathematics, poetry, dancing, music and more.