This review states that heat stress can significantly disrupt the hypothalamic-pituitary-gonadal axis in males, and that heat stress directly damages the testes, reducing testosterone synthesis. It also says that human and animal studies have shown negative effects on male reproductive function, including reduced testosterone and androgen levels.

In hot ambient conditions, male baboons had lower fecal testosterone levels than in cooler months, even after accounting for age and individual differences. The study states that higher average daily maximum temperatures were associated with lower fecal testosterone, suggesting that heat can directly affect testes without activating the HPA axis.

A large body of evidence reports detrimental effects of acute heat stress on testis function, particularly on spermatogenesis and steroidogenesis, in both animal and human models. The review explains that the testis is especially vulnerable because it normally functions at a scrotal temperature 2°C–4°C below core body temperature.

We found that male mice were more susceptible to development of heat-induced hyperthermia than females, and this was prevented by castration, not by castration with testosterone replacement. These results suggest that testosterone mediates heat-induced hyperthermia and is a heat stress susceptibility factor.

The analysis shows that breeding season length and mating system are the strongest predictors of average testosterone concentrations, while breeding season length, environmental temperature, and precipitation variability are the strongest predictors of within-population variation in testosterone. Shorter breeding seasons are associated with higher mean testosterone levels and lower variation in testosterone.

In the experiment, compared with controls, both the exertional heat stroke onset group and the day-3 post-heat-stroke group had significantly lower plasma testosterone values. The paper links heat stress with decreased testosterone in male rats.

Repeated exposure to hot and cold thermal stress significantly decreased cortisol levels in young men who were regular sauna users, but it did not induce significant changes in testosterone, prolactin, or DHEA-S concentrations.

In male M. namaquensis, simulated heatwave conditions caused a significant decrease in plasma testosterone levels compared with controls. The paper also reports that both study species experienced reduced fertility indices under heatwave conditions.

The study reports that testosterone coordinates physiological, morphological, and behavioral traits during reproduction and that many of these traits are under sexual selection. In this wild songbird, males with higher testosterone during the mating phase had higher annual reproductive success, suggesting that selection may act positively on testosterone during mating periods.

The article states that acute physiological stress induces predictable, transient reductions in testosterone and temporary impairments in sexual function, driven by sympathetic activation, HPA-axis engagement, and energy imbalance. This supports the broader claim that stress physiology tends to suppress rather than elevate testosterone.

In males, sustained exposure to high heat levels can hinder testicular steroidogenesis and spermatogenesis, which in turn reduces testosterone levels and semen quality. The article summarizes evidence that heat stress generally suppresses male reproductive hormone production.

The study found reductions in testosterone immediately after resistance exercise under heated conditions, and concludes that exercise in a hot environment could be influenced by thermoregulatory responses to heat stress and by decreases in testosterone.

The paper states that testosterone commonly mediates reproductive effort and that, across wild primates, male testosterone varies most closely with aggressive mating competition rather than with reproductive physiology. It concludes that males often increase testosterone when competing for access to females, consistent with the challenge hypothesis.

Our results showed that exposure to an acute thermal stressor caused reductions in the male reproductive hormone testosterone. The authors describe this as the first evidence of sub-lethal effects of an acute thermal stressor on the reproductive and stress endocrine axis of an amphibian species.

The article reports that elevated temperatures adversely affect testosterone production in ex vivo porcine testicular tissue, suppressing expression of key steroidogenic enzymes and reducing testosterone synthesis capacity.

When exposed to simulated heatwave conditions, both species experienced a marked reduction in testosterone levels and seminiferous tubule diameters, indicating a decline in fertility markers. The article also notes that exposure to high temperatures and hyperthermia can disrupt male fertility through negative effects on testosterone synthesis.

The article proposes that short breeding seasons and, perhaps, environmental conditions at high altitudes can create conditions under which high testosterone levels are beneficial in tropical birds. It argues for refining the idea that tropical birds generally have low plasma testosterone.

Thermal stress had an inhibitory effect on gonadal development and reproduction, and hemolymph testosterone levels showed a decreasing trend under high-temperature exposure. The paper explicitly states that high-temperature stress significantly decreased testosterone in male Pacific abalone.

The study found that men with higher levels of physical activity had higher testosterone concentrations both before and after the sauna bath. This is not direct evidence about Kalahari populations, but it is relevant to the idea that endocrine state can covary with activity or stress exposure.

A meta-analysis found that voice pitch, height, and testosterone predicted mating outcomes, and that men with higher circulating testosterone, measured in blood or saliva, invested more in mating effort, including greater interest in casual sex. The authors note that testosterone is commonly argued to motivate investment in mating effort, although causal direction cannot be established.

A review of ambient temperature and testosterone states that multiple animal and human studies have shown increased ambient temperature reduces testosterone secretion. It cites older animal work showing high ambient temperature is detrimental to testosterone secretion in rams and argues that glucocorticoids may mediate the temperature-testosterone link.

The review states that thermal shock can heavily affect spermatogenesis, and that environmental temperature influences testicular function because the scrotum normally maintains the testes 2°C–4°C below core body temperature. It describes heat stress as detrimental to steroidogenesis.

The paper reports that men's testosterone levels are suppressed in response to infant cues and interprets this as evidence for the importance of pair bonding and paternal care in human evolutionary history. It also frames testosterone as part of a tradeoff between mating effort and parenting effort.

The article discusses prior work by Gomes, Butler, and Johnson (1971), noting that a high ambient temperature reduced testosterone production in the ram, and it frames camel reproductive cycles as potentially influenced by thermal stress.

The article says body weight significantly decreased at 40°C and serum testosterone decreased in both groups, concluding that heat stress adversely affects male reproductive functions and is associated with hormonal imbalance and reduced spermatogenesis.

In wild rock hyrax, copulation success increases with rising testosterone in males. The study found sexually opposite effects of testosterone, with higher testosterone associated with greater male reproductive success and lower female copulation success.

The German-language review says that although spermatogenesis is temperature-dependent, a clear relationship between climate warming and reduced testosterone levels is not currently evident, and further studies are needed. This is useful as a contrasting source because it rejects a simple heat-to-low-testosterone inference in humans.

The authors report that climate and ecology, especially temperature seasonality, predict latitudinal trends in sexual selection across birds. They conclude that climatic conditions leading to short, intense breeding seasons increase the potential for polygamy and strengthen sexual selection.

In the West African dwarf buck, serum testosterone levels were stable in the barn except for a seasonal drop, but exposure to heat stress was associated with large deviations from unexposed animals. The study concludes that high ambient temperatures could seriously alter androgen metabolism and utilization.

This paper reports significant reductions in serum testosterone and LH in animals exposed to heat stress, and concludes that heat stress caused a drastic impairment of male reproductive function.

The article reports that testosterone levels can vary by season and that testosterone was lower in cold months than in hot months, but it does not address Kalahari populations or indicate that elevated circulating testosterone reflects an active sexual-selection axis under thermal stress.

In a study of San men living in a desert environment, no evidence for elevated estrogens was found and the males showed endocrine levels comparable with European and South African Negro values. The article suggests that ovarian suppression may exist to limit conception to times of high nutrition.

This claim is not directly supported by the retrieved sources. The available literature instead more consistently shows that heat stress tends to reduce testosterone or leave the climate-testosterone relationship unresolved, rather than indicating that elevated circulating testosterone persists despite thermal stressors in a Kalahari male population.

The page is a general health article about summer heat and hormones. It provides practical advice but does not offer primary evidence relevant to the claim about Kalahari males, testosterone, or sexual selection.