Shouldn’t they happen at around the same age?
In: 9
Ugh…answering this question is going to be messy. When we discuss why evolution has selected for some traits in humans over others, we’re talking about the situations humans most often found themselves in for most of our existence. And those situations are much darker than our situation today.
It was wasn’t too uncommon for girls to be married off at a young age a few hundred years ago, and still happens in some corners of the world. It’s not a stretch to extrapolate that this used to be the norm going back further into pre history when humans did most of their evolving.
To raise children to adulthood requires time and energy from the mother, and resources and physical protection from the father since a pregnant woman is less capable of gathering resources safely. It’s easier for females to uphold their requirements at a younger age. While males would on average take more time to accumulate resources/strength to uphold their end. Thus evolution would select for males entering the game at a later stage.
No one knows for certain.
It’s worth noting that the average year to begin puberty is only about a year apart, so they *do* happen around the same age. But there can be a lot of individual variance, which is influenced by all kinds of environmental and genetic (and, as we’re finding out, epigenetic) factors.
However, some theories include:
* Females have fewer opportunities to reproduce than males (due to pregnancy requiring a lot more time and bodily resources), so their window in which to do it needs to begin sooner than males to raise the chance of having more healthy babies.
* Pubescing slightly earlier encourages reproduction with males that are slightly older and have had more time to build the skills and abilities for survival.
* It usually takes some time after the initial onset of puberty to actually be capable of producing children. In girls, this requires more metabolic energy and physical development than boys, so puberty needs to begin earlier for girls to kick off that process so they have a better chance of being more or less equal with boys by the time it’s physically safe to bear children (roughly late adolescence).
[Here’s a paper](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7543877/) that explains a bit about the mechanisms of puberty. An excerpt:
*Infusion of human kisspeptin-10 (KP10) into the ME of female and male rhesus monkeys at both the prepubertal and pubertal stages stimulates GnRH release in a dose-responsive manner (39,40). Importantly, within the same sex the GnRH neurons in pubertal animals are more sensitive to KP10 than in prepubertal animals, as GnRH response to KP10 at the same dose in pubertal animals is larger than in prepubertal animals. Interestingly, female GnRH neurons are ten-fold more sensitive than male GnRH neurons, as 1) the minimum effective dose is 10-fold less in female than male and 2) KP10 at 0.1 μM induces a larger response in females than in males (33). Pubertal amplification of KP10 action on GnRH release in females is due to the pubertal increase in estradiol, as there is no GnRH response to KP10 in ovariectomized pubertal females (39). Unlike in females, however, the GnRH response to KP10 in males is less dependent on the pubertal increase in androgens, as orchidectomy in pubertal males does not alter the GnRH response to KP10 (33). Therefore, the contribution of kisspeptin signaling to the pubertal increase in GnRH release in both males and females is two folds: 1) a larger amount of endogenous kisspeptin output after puberty onset and 2) an increase in kisspeptin receptor sensitivity of GnRH neurons.*
TL;DR: genders have genetic and morphological differences.
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