Fluctuating Testosterone and Men’s Behavior

Everyone knows that testosterone is the male sex hormone, but few appreciate how important and flexible this little chemical is the determination of male behaviors. Testosterone is produced largely in the testes and drives the development of much of what makes men manly. It promotes the growth of muscles, body hair, and of course, male sex organs, but it also masculinizes the brain and plays a role shaping men’s behavior. All human thoughts and behaviors are the result of chemical reactions in the brain, and hormones like testosterone can change our goals and interests, our desires, and our willingness to take risks. Although men have on average 7–8 times as much free-flowing testosterone in their blood as women, these levels fluctuate throughout the day and as individuals perform different tasks. The causation is bidirectional, meaning that certain behaviors can cause changes in testosterone levels and changes in testosterone levels can cause changes in behavior. Testosterone is related to aggression and competition, as well as sexual interest and pursuit. Competitive sports, for instance, have been known for some time to increase men’s testosterone. Competition is not the whole story though, because one study showed that cutting down trees like a lumberjack resulted in an almost 50% increase rise in testosterone, significantly more than playing a competitive game of soccer. After watching porn, men can expect a spike in testosterone of about 35% for an hour or two.

A Perfect Storm

In one recent study, researchers noted that elevated testosterone can actually make men more persistent (or stubborn), such that they spend more time trying to solve an unsolvable puzzle. It seems that spikes in testosterone can make men less deterred by failure. This could be both good or bad, as sometimes persevering in the face of difficulties is a precursor to success (for example, in one’s career), but sometimes it’s a waste of time and energy. Some researchers have proposed that this heightened persistence might be adaptive for men trying to find a mate. Elevated levels of testosterone make men interested in sex, willing to fight and compete, and persistent—a perfect storm for finding, impressing, and convincing a potential sexual partner.

On average, heterosexual women find men that are more masculine to be more attractive when they are at the most fertile phase of their menstrual cycle (they prefer less masculine men when they are less fertile or pregnant).

The evolutionary goal of spikes in testosterone is making babies. In this sense, our brains are similar to those of our caveman ancestors or our animal relatives. On average, heterosexual women find men that are more masculine to be more attractive when they are at the most fertile phase of their menstrual cycle (they prefer less masculine men when they are less fertile or pregnant). Interestingly, men in long-term relationships can expect a drop in testosterone. Married men and men in long-term committed relationships typically have lower levels of testosterone than single men or men in new relationships. Presumably, this reduced testosterone makes these men less interested in the hunt for a new mate. Furthermore, men who are in polyamorous relationships or are interested in extra-pair sexual activity (like cheating) also exhibit elevated testosterone.


Fathers have especially reduced levels of testosterone. Reduced testosterone is thought to promote relationship building and caring for children instead of aggression and pursuing new mates. From an evolutionary perspective, this behavioral shift is important to ensure that after a man secures a mate and produces offspring, his offspring are provided with adequate care. This reduction in testosterone may also be one reason why many married men feel more content and less lustful than their single counterparts. In the end, changes in testosterone are important for many significant transitions in a man’s life and personality: puberty, finding partners, building long-term romantic relationships, and starting and caring for a family.   Mars Explore Further



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Zachary Durisko, PhD – Freelance writer, editor, and scientist. Research Fellow, Evolutionary Ecology of Health Research Laboratories, McMaster University, Ontario. Dr. Durisko is a researcher in Evolutionary Psychiatry and Behavioral Ecology with several peer-reviewed academic articles. His research focuses on how human history has shaped the way we think. His work is revolutionizing how we understand mental illness, especially depression. His PhD is in Psychology, Neuroscience, and Animal Behavior.


Farrelly D, Owens R, Elliot HR, Walden HR, Wetherell MA (2015).

The effects of being in a “new relationship” on levels of testosterone in men. Evolutionary Psychology 13(1): 250–61. Pirke KM, Kockott G, Dittmar F (1974).

“Psychosexual stimulation and plasma testosterone in man”. Arch Sex Behav 3(6): 577–84. Torjesen PA, Sandnes L (2004). Serum testosterone in women as measured by an automated immunoassay and a RIA. Clin. Chem. 50(3): 678. Trumble, BC, Cummings DK, O’Connor KA, Holman DJ, Smith EA, Kaplan HS, Gurven MD (2013).

Age-independent increases in male salivary testosterone during horticultural activity among Tsimane forager-farmers. Evolution and Human Behavior 34(5): 350–357. Welker KM, Carré JM (2015).

Individual differences in testosterone predict persistence in men. European Journal of Personality 29: 83–9.

Written by: Z. Durisko

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