It was recently reported in the popular press that becoming a father was associated with a drop in testosterone level. It seems intuitive that it is not the act of fathering the child (9 months prior) that leads to this, but rather living with the baby / baby's mother that causes testosterone to fall. If so, this mechanism should apply to any other males in proximity such as older siblings of the baby, grandparents and uncles, or what have you. A putative evolutionary mechanism put forth for this (by Sarah Hrdy; see link) is that male aggression is associated with infant mortality; perhaps lower testosterone leads to less aggression?
Fascinating, but this is about cancer prevention. Higher levels of testosterone are associated with higher prostate cancer risk (a phenomenon which has been invoked to explain racial disparities in prostate cancer incidence). Just as repeated pregnancies and consequent lower estrogen levels confer protection against (estrogen-associated) breast cancer, one would predict that incidence of prostate cancer would go down as number of consecutive babies in the house goes up.
If true, the next thing is to determine how it happens. It might be behavioral - maybe the male needs to be in the presence of fussy baby to get lower testosterone. If pheromonal, the male could just share air/living space with baby and never see or hear it. If the latter, it presents the possibility that baby pheromones might be bottled and then used over the long term as a natural testosterone suppressant for prostate cancer prevention.-- bungston, Nov 03 2011 Testosterone and fatherhood http://brainblogger...-building-a-family/ [bungston, Nov 03 2011] Mothers and others http://www.amazon.c...=mothers+and+othersHrdy's research deals a lot with infanticide by males in various contexts and the evolutionary pressures this produces. [bungston, Nov 03 2011] I didn't read the idea, but arn't babies heads a little large for this even though they routinely make it past the birth canal?-- rcarty, Nov 03 2011 After reading the idea my two cents is that the testosterone decrease is related to reduced sexual intercourse.-- rcarty, Nov 03 2011 [bungston] you're an idiot but I quite like you...-- po, Nov 03 2011 This idea makes perfect sense. Nature born subconscious self preservation made me do it baby!-- vfrackis, Nov 03 2011 There's a much simpler way to lower testosterone levels.-- mouseposture, Nov 03 2011 Eat more kudzu.-- Alterother, Nov 04 2011 random, halfbakery