Sounds crazy, but according to this study published in the Proceedings of the National Academy of Sciences of the United States of America and conducted in the Philippines, this is no joke.


Every body has some T in varying levels. Those with testes produce more (T is made there!), though levels still vary. Here is just a few of it’s functions in those with testes (1):

  • Bone density

  • Fat distribution

  • Muscle strength and mass

  • Facial and body hair

  • Red blood cell production

  • Sex drive

  • Sperm production



Yes! Ok, so to set you up, in a large representative study between 2005-2009 both morning (AM) and evening (PM) Testosterone (T) levels were tested as T levels tend to peak in the AM and decline throughout the day.

 Here are  some of the fascinating findings from this study (2):

Not only did T levels shift from parenthood, but single men with higher T levels in the beginning of the study, were more likely to end up partnered or with a child by the end of the study than single men that had lower T levels to start. 

They also tested whether those who became newly partnered new fathers in 2009 experienced a greater decline in T relative to men who remained single non-fathers between 2005 and 2009. Men who were both newly partnered and new fathers showed the largest declines in AM and PM T between 2005 and 2009 and their declines in both AM and PM T were significantly greater than the modest age-related declines in AM and PM T observed among single non-fathers.

They also looked at whether the age of the father's child mattered. Although all new fathers, regardless of their youngest child's age, experienced a significant reduction in AM and/or PM T compared with non-fathers, fathers with newborns (1 mo old or less) at the time of follow-up hormone assessment showed significantly greater declines in AM and PM T compared with fathers whose youngest child was older than 1 y of age, removing other factors (like stress, sleep etc.) Men with newborns also differed significantly for AM T compared with men with infants between 1 mo and 1 y of age.

 And, when looking at whether men who were fathers in 2009 varied in T based on their self-reported involvement in childcare, controlling for other factors, Men reporting 1–3 hours of daily childcare had significantly lower AM T compared with fathers reporting not being involved with care, whereas fathers reporting the highest involvement in childcare (3 hours or more per day) showed significantly lower values of both AM and PM T compared with men reporting no care.


It has long been thought that higher T levels are connected with mating success as T tends to bolster traits like mating effort and attractiveness like musculature (3), motivation to win (4) and pursuit of social dominance (5). But, while helpful in securing mates, many T-stimulated behaviors “may conflict with partnership stability and parenting (6). “ As this study points out, men with higher T levels are more likely to have marital problems and to be divorced (6), whereas men with lower T have been found to spend more time with their partners (7). In an experimental setting, men with greater T also reported feeling less sympathy or need to respond to infant cries compared with men with lower T (8).

So this study basically shows that nature is really, really smart. The body biologically switches gears from an investment in mating to an investment parenting to help facilitate their role as caregivers! Wild.

Written by: CYCLES+SEX Staff


  1. Mayo Clinic. “Testosterone therapy: Potential benefits and risks as you age.” mayoclinic.org https://www.mayoclinic.org/healthy-lifestyle/sexual-health/in-depth/testosterone-therapy/art-20045728

  2. Gettler, Lee T, McDade, Thomas W, Fernail, Alan B, Kuzawa, Christopher W., “Longitudinal evidence that fatherhood decreases testosterone in human males” Proceedings of the National Academy of Sciences. (2011) 16194-16199

  3. Bribiescas, Richard G. “Reproductive Ecology and life history of the human male.” American Journal of Physical Anthropology (2002). 148–176.

  4. Salvador A, Suay F, González-Bono E, Serrano MA. “Anticipatory cortisol, testosterone and psychological responses to judo competition in young men.” Psychoneuroendocrinology (2013) 28:364–375.

  5. Archer J. “Testosterone and human aggression: An evaluation of the challenge hypothesis.” Neurosci Biobehav (2006). Rev 30:319–345.

  6. Booth A, Dabbs JM. “Testosterone and men's marriages.” Soc Forces (1993). 72:463–477

  7. Gray PB, Kahlenberg SM, Barrett ES, Lipson SF, EllisonPT. “Marriage and fatherhood are associated with lower testosterone in males.” Evol Hum Behav. (2002) 23:193–201

  8. Fleming AS, Corter C, Stallings J, Steiner M. “Testosterone and prolactin are associated with emotional responses to infant cries in new fathers.” (2002) Horm Behav 42:399–413