Randy Thornhill – författare

Research conducted over the last fifteen years has placed in question many of the traditional conclusions about the evolution of human female sexuality. Women have not lost estrus, as earlier researchers thought, but it is simply concealed, resulting in two functionally distinct sexualities with markedly different ends in each phase. At the fertile phase of the cycle, women prefer male traits that may mark superior genetic quality, and at infertile phases, they prefer men willing to invest resources in a mate. Thus, women's peri-ovulatory sexuality functions to obtain a sire of superior genetic quality, and is homologous with estrus in other vertebrates. This model sheds light on male human sexuality as well: men perceive and respond to women's estrus, including by increased mate guarding. Men's response is limited, compared to other vertebrate males, implying coevolutionary history of selection on females to conceal estrus from men and selection on men to detect it. Research indicates that women's concealed estrus is an adaptation to copulate conditionally with men other than the pair-bond partner. Women's sexual ornaments-the estrogen-facilitated features of face and body-are honest signals of individual quality pertaining to future reproductive value.

Research conducted over the last fifteen years has placed in question many of the traditional conclusions about the evolution of human female sexuality. Women have not lost estrus, as earlier researchers thought, but it is simply concealed, resulting in two functionally distinct sexualities with markedly different ends in each phase. At the fertile phase of the cycle, women prefer male traits that may mark superior genetic quality, and at infertile phases, they prefer men willing to invest resources in a mate. Thus, women's peri-ovulatory sexuality functions to obtain a sire of superior genetic quality, and is homologous with estrus in other vertebrates. This model sheds light on male human sexuality as well: men perceive and respond to women's estrus, including by increased mate guarding. Men's response is limited, compared to other vertebrate males, implying coevolutionary history of selection on females to conceal estrus from men and selection on men to detect it. Research indicates that women's concealed estrus is an adaptation to copulate conditionally with men other than the pair-bond partner. Women's sexual ornaments-the estrogen-facilitated features of face and body-are honest signals of individual quality pertaining to future reproductive value.

This book develops and tests an ecological and evolutionary theory of the causes of human values—the core beliefs that guide people’s cognition and behavior—and their variation across time and space around the world. We call this theory the parasite-stress theory of values or the parasite-stress theory of sociality. The evidence we present in our book indicates that both a wide span of human affairs and major aspects of human cultural diversity can be understood in light of variable parasite (infectious disease) stress and the range of value systems evoked by variable parasite stress. The same evidence supports the hypothesis that people have psychological adaptations that function to adopt values dependent upon local infectious-disease adversity. The authors have identified key variables, variation in infectious disease adversity and in the core values it evokes, for understanding these topics and in novel and encompassing ways. Although the human species is the focus in the book, evidence presented in the book shows that the parasite-stress theory of sociality informs other topics in ecology and evolutionary biology such as variable family organization and speciation processes and biological diversity in general in non-human animals.