Men's tendency toward large-group dynamics fosters competition and system-building. Women's focus on one-to-one relationships, rooted in the mother-child bond, cultivates intimacy and emotional expressiveness. These distinct social orientations help explain many psychological differences between the sexes.

Unlike most species, human females don't display overt fertility signs. This evolutionary trait encourages stable pair-bonding, as males must invest in a long-term relationship. It also reduces rivalry and aggression, fostering a more cooperative approach to raising children.

'Cowgirling' is a term from polyamorous communities where one woman strategically eliminates rivals to make an open relationship monogamous. This competitive behavior reveals that even within non-monogamous structures, the underlying evolutionary drive for mate-guarding and exclusivity often prevails.

Contrary to being an evolutionary 'paradox,' research suggests same-sex sexual behavior in animals is a functional adaptation for survival. Its prevalence increases in species facing greater external threats, such as extreme climates or high numbers of predators. This indicates the behavior serves to strengthen social cohesion and cooperation, which are critical for group survival under stressful conditions.

Data and observation suggest women's sexual orientation is more fluid throughout their lives. Women are more likely than men to identify as straight for a period and later form same-sex relationships, indicating a higher degree of plasticity in female sexual preference.

The "gender egalitarian paradox" shows that as societies become more equal and competitive, men and women diverge more in personality. This environment may activate latent sex-specific adaptations, with women becoming more prone to anxiety and men engaging in more risk-taking behaviors.

Women may have evolved to signal vulnerability to evoke care. This can translate into a political preference for systems that transfer resources to the vulnerable, a group they may see themselves in. This preference helps construct a social world that aligns with their evolved interests.

The influential theory of universal female sexual fluidity relies on a definition that encompasses non-sexual emotional closeness. By asking "why should we privilege the sexual over the emotional?", the theory redefines close friendship as a form of sexual fluidity, creating a misleading claim.

Congenital Adrenal Hyperplasia (CAH) exposes XX fetuses to high levels of androgens. As adults, these women are statistically more likely to have a same-sex orientation than the general population, providing a clear "natural experiment" linking prenatal hormones to human sexual preference.