Library.

“Apart from mane traits, lions exhibit no sexual selection.”

Lions display several forms of sexual selection beyond mane characteristics. Research documents male coalition competition for breeding access, female mating strategies and preferences, and infanticide linked to male reproductive advantage. Although some cited links are inaccessible or duplicate the same research, multiple peer-reviewed studies directly refute the claim’s absolute wording.

“In males living in the Kalahari environment, elevated circulating testosterone indicates that a sexual-selection-related physiological axis remains active in the population despite thermal stressors.”

The claim is not supported by the cited evidence. The only directly relevant study of desert-dwelling human males does not show elevated testosterone, and the broader heat-stress literature mostly points in the opposite direction: thermal stress tends to suppress testosterone and impair reproductive physiology. The inference to an active sexual-selection-related axis in Kalahari males is therefore unproven.

“Thermal selection and sexual selection can act in opposite directions in shaping organismal phenotypes.”

The evidence strongly supports the possibility of opposition between thermal selection and sexual selection. Multiple empirical and review sources show cases where traits favored for mating success are penalized under thermal stress, reducing heat tolerance, survival, or performance. Because the claim says these forces can act in opposite directions, documented examples are sufficient to establish it.

“Physiological costs of expressing sexually selected traits (for example, elevated thermal loads) can oppose natural selection that would otherwise favor smaller or less ornamented phenotypes, especially under environmental stress.”

The evidence strongly supports this evolutionary trade-off. Multiple peer-reviewed studies show that sexually selected traits can impose thermal, metabolic, immune, or fertility costs, and these costs often become more important under environmental stress. Cases where species evolve compensatory heat tolerance do not refute the point; they confirm that the traits can carry real physiological burdens.

“Testosterone is the principal endocrine mechanism by which sexual selection translates into morphological sexual dimorphism.”

The evidence shows testosterone is an important and often central hormonal mediator of sexually selected, male-typical morphology in many vertebrates. But the claim goes too far by presenting it as the principal endocrine mechanism in general. Credible sources show multiple alternative hormonal pathways and taxon-specific exceptions, so the broad formulation is only partly supported.