It is well documented that men who have impaired production or sensitivity to testosterone have an even less prominent brow, rounder face, and so forth. The authors found that, over the past 80,000 years, there have been a few gradual changes in the structure of the human face. Some skulls came from human remains that were over 80,000 years old, some were close to 40,000 years old, some 10,000 years old, and many modern skulls as well. If they suddenly appeared before us now, early humans would not look quite right to us. Despite the name "anatomically modern humans," the members of the species Homo sapiens sapiens that lived 200,000 years ago did not look exactly the same as humans do now. This greater muscle mass allows males to gain greater acceleration, speed, and more powerful striking movements. In all living hominid species, males are more muscular, allowing them to have more strength and power. A 2020 study reported that women tend to find a man more attractive if the man's previous relationships ended mutually, and less attractive if the man was dumped. It was concluded that societal-level ecological factors impact the valuation of traits by combinations of sex- and stress-hormones. While women from the United Kingdom preferred the faces of men with low cortisol levels, women from Latvia did not discriminate between men with either high or low levels of cortisol. I will review recent case studies supporting the evolutionary potential hypothesis and suggest micro-evolutionary experiments to unravel the mechanistic basis of life-history evolution. These studies suggested that a man in his 60s in the 2000s had lower testosterone levels than a man in his 60s in the 1980s. For instance, a study spanning from the 1980s to the early 2000s highlighted a consistent decrease in average testosterone levels irrespective of age. This study, among others, indicated that testosterone levels in men were not merely decreasing due to aging but also because of generational shifts. In a landmark study by Travison et al. (2007), a significant decline in serum testosterone levels was observed in a cohort of men over a 20-year period. The first signs of declining testosterone levels emerged from longitudinal studies conducted over several decades. The concept of sexual selection was introduced by Charles Darwin as an element of his theory of natural selection. According to research presented at the 2020 American Urological Association Virtual Experience, testosterone levels have continued to drop from 1999 to 2016. Studies show lead exposure may alter male sex hormones, thus impeding endocrine function and Sertoli cells. The transition from the nomadic lifestyle of hunting and gathering to a more settled existence during the Agricultural Revolution would have resulted in a slight decline in testosterone levels. While researchers have called this trend "alarming" from an evolutionary standpoint, history does paint a picture of a continual rise and fall in historical testosterone levels over the centuries based on different social and environmental shifts. Understanding normal testosterone levels by age provides important context for evaluating this trend. Selection preferences are biologically driven, that is, by the display of phenotypic traits that can be both consciously and unconsciously evaluated by the opposite sex to determine the health and fertility of a potential mate. Since a human erection relies on a hydraulic pumping system, erection failure is a sensitive early warning of certain kinds of physical and mental ill health. The effects on the human brain formation during puberty is directly linked to hormones changes. One study found that a four-inch increase in waist size increased a man's odds of having low testosterone by 75%. These lifestyle changes may have resulted in a "de-seasonalization" of human reproduction and possibly in testosterone fluctuation. This 2019 study suggests that during industrialization, humans were progressively and increasingly shielded from both daylight duration by indoor work, and environmental temperature by heating and air conditioning. Ancient diets were high in polyunsaturated fat (healthy fats), fruits, and vegetables, and consumption of grains and dairy was low, another pattern found to be supportive of healthy T levels. As testosterone levels decline and societal norms evolve, there is a need for more inclusive and diverse representations of masculinity in media and popular culture. The decline in men’s testosterone levels over generations not only has physiological implications but also profound societal and psychological impacts. The recognition of these factors is a crucial step towards mitigating their impact and potentially reversing the trend of declining testosterone levels. The industrialization era has brought about significant lifestyle changes that indirectly impact testosterone levels. The shift towards highly processed foods has resulted in diets high in refined sugars, unhealthy fats, and preservatives while being low in essential nutrients critical for maintaining optimal hormone levels.
