Fifteen months ago I gave birth to a baby girl. The child is now a seam-popping twenty-five-plus pounds. Babies, they grow so quickly it's creepy -- my thoughts fast-forward through her teething years to the teens -- and I'm terrified. Problem is, my family lives in New York City where children grow up too quickly. The weenies of tweens should stay in their jeans, but all too often they don't.
The age at which a teenage girl starts to become sexually active depends a lot on her social environment -- peers, culture and so on. It especially depends on the family environment, according to a recent study by Australian behavioral ecologists Fritha Milne and Debra Judge. But here's the thing: family environment is not necessarily influential for the expected reasons, such as curfews and chastity pledges and other parentally-imposed restrictions.
The hidden influence is the younger sibling.
Milne and Judge recruited nearly 200 women and 76 men, all living in or around the city of Perth, Australia, and asked them questions about their family lives and sexual development. The results were that girls with younger brothers only (no sisters) lost their virginity an average of more than a year later (at age 18.3) than girls with younger sisters only. Girls with both younger brothers and sisters lost it nearly two years later on average (age 19.3) than girls with no younger siblings. Younger sisters alone had no impact.
The chastity effect only applied to girls with younger brothers. Having a big brother (or sister) didn't make a girl any less likely to hold onto her virginity. Yet another strange pattern emerged. This one involved the girls' physical maturity.
The more older brothers a girl had, the later she got her first period. Girls with only elder brothers got their first visit from "Aunt Flo" up to a year later (at age 13.6) than girls with older sisters or no older siblings (age 12.7). (This is meaningful given that breast cancer and other conditions are related to earlier menstruation.)
Elder brothers delay physiological maturation, while younger brothers delay behavioral maturation.
What's going on?
Trained as behavioral ecologists, Milne and Judge took a look at the big picture. Daughters are often caregivers. Historically -- and in traditional societies -- a woman with daughters as first- or second-born children has a larger family than a mom whose first children were sons. Elder daughters take care of younger siblings, which frees up Mom to keep popping them out. Boys historically required more resources than do girls, which made a big sister's contributions even more important. As a result, these helpful elder daughters experience a delay in starting their own families. In the modern world where women don't usually start their families until their mid-twenties on average, this is no problem. In the past, females with brothers may have had fewer children over their lifetimes.
The bigger mystery is what's actually behind Big- and Little Brother's stalling effect on their sisters' sexuality. This is unknown territory, so Milne and Judge tread lightly here. The safest theory is that the delays are behavioral. Girls with little brothers lose their virginity later because they're too busy taking care of their siblings to have love lives of their own. Perhaps little brothers, who are slower than female siblings to develop and reach puberty, keep their elder sisters in a more childish mindset. Or perhaps the stress of caregiving slows down puberty.
The researchers should also consider a much more surprising yet equally plausible theory: brothers send out chemical cues (pheromones) in their sweat that inhibit their sisters' sexual development. Odd as it sounds, this would explain the perplexing finding that girls with older brothers get their first periods later than their peers. And, it appears, so do girls who grow up with their biological fathers in the household, compared to their peers with absent dads. Several studies, including here and here and a large one at Penn State that involved over nineteen hundred college students, came to this conclusion. (Interestingly, the same study found that girls growing up in homes with males unrelated to them got their periods earlier than average, suggesting that a non-related male may speed up sexual maturity.)
The sweat-stifles-sexuality theory isn't as far-fetched as it sounds. Other animals -- rodents, for instance -- use pheromones to modulate sexual maturity and fertility in a population. Over the years, a girl would inhale chemical cues in fraternal sweat -- think of all those sock and armpit odors. Those chemicals would hit the hypothalamus of her brain where sex hormones are produced, and slow down the works. The result is that puberty strikes a little later. Evolutionarily speaking, this allows girls to stay in the family nest longer without conflict. The risk of incest is reduced.
Knowing all this, should I try for a son so that my daughter will benefit from the younger-brother effect? Truth is, the data applies to populations, not individuals. There are no guarantees; these are just interesting findings that merit more research. Moreover, I'm in over my head right now with my baby girl's teething and feeding challenges. Sure, I'll want preserve her girlhood for longer than a New York minute. But I also need to preserve my sanity.
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"Elder brothers delay physiological maturation, while younger brothers delay behavioral maturation." These claims are extremely thin and speculative. While I am inclined to suspect there are chemical/physiological dynamics at play when it comes to patterns of having "Aunt Flo" show up, I go the opposite direction on the matter of behavioral maturation.
The correlation between various siblings and sexual activity (which is not the same as behavior maturation, for the record) can be explained by cultural and social forces, less than any deep psychological or behavioral causality. You have immediate family peers. You have peers watching you... which can impact behavior in a variety of ways, given the cultural context.
I really like this topic.
However, I wish the HuPo bloggers would dig into the fascinating questions on these matters rather than pushing their own opinions and making wild claims. Article after article, we see this same pattern.
Perhaps HuPo needs more siblings on the editorial staff.
- 1 out of 3 girls says parents most influence their decision about sex
* Parents - keep promoting abstinence
What I know, is having older brothers can drive guys away. All through high school, a guy would flirt then stop talking to me. Then I found out my brothers went around scaring them off.
Ugh.
This article doesn't even acknowledge basic social and cultural reality, but instead tries to make this all cognitive science or about physiology.
We're social and cultural beings.
Why is that a benefit, to stunt somebody's development?
1 in 3 sexually active teens get pregnent
1 in 4 teens have an STD
- why stop all the fun
This is also true of girls who have a father living in the house. I read a study about it years ago and it came to the same conclusion/speculation about pheromones. So the question I have is, were these two parent families? Or were they single parent families? It might make a difference in the results.
Humans naturally mature at an expedited rate upon the introduction of a non-biological adult of the opposite gender. It specifically states having a big brother or the biological dad (or sisters) in the picture made no difference.
Personally, I think it is sad kids are forced to grow up so quickly. Many encourage young girls to take birth control pills, rather than abstaining. Many men have absent fathers so they don't have a positive male role model in his life to teach him how to treat a woman right, and when sex should be introduced in a relationship.
As our society begins to experience a collapse of social norms in an effort to have "free expression" I fear we will see more unwed mothers, absent fathers, and children questioning where they came from. We need to encourage the re-weaving of the moral fabric once holding our country together before we lose children and the future for multiple generations.
Alright let me be careful with what I say here, because the moderator just blocked my first reply. I think you should re-read the above paragraph. Your summation is a bit simplistic. Also, by bringing up the notion that it is the daughter who is attracted to her father seems to imply something that is very wrong. Therefore, it is hard to take your moral lecture very seriously.