CogBlog

It is important to note that the phenomenon of early menarche due to turbulent childhood environments is only applicable to females. Only females, not males, raised in these environments have a significant shift in reproductive age. Therefore, we should look to differences between males and females to account for this disparity in developmental age. I think degree of parental investment is a large factor. The fact that girls (unlike boys) mature physically before being fertile indicates that there was a selection pressure for a “preparatory period” to allow girls to develop the skills necessary for good mate selection and effective child care. A mature-looking girl is more likely to attract male attention and be permitted child care responsibilities than an immature-looking one. Thus, in our ancestral past, early physical maturation facilitated girls’ abilities to assess male worthiness and develop skills for child-rearing. This extended preparatory period (even though it cuts into the reproductive lifespan) offers great advantages, especially in a stable environment where a future mate is likely. However, in an unstable environment, evolution may have groomed us to drop the preparatory period, reach menarche, and start producing while it was still feasible.
Another interesting point is that humans have shifted from reaching menarche around age 16 (in hunter-gatherer societies) to age 12 (modern societies). This may indicate a reduced need for an extended preparatory period because of the number of resources we have to raise a child in today’s societies. I think even most impoverished societies have lower infant mortality rates than our hunter-gatherer ancestors.

I am with Katie. A girl I knew growing up was a little on the fuller side. She had two happily married parents and no perceivable threats (at least from an outsiders view) and she started menarche in second grade. But it is only one incident so I don't know if that is anything to go on. I can't really see any evolutionary benefits to a second grader getting pregnant. I wouldn't think they would be able to take care of a baby.
However, if the menarche is only a couple years earlier than normal I could see the evolutionary benefits in getting an edge on the reproductive game.

I do think evolution may play a role in the age at which a girl reaches reproductive maturity, but what about the role of body fat? I had always heard that girls with more body fat would reach maturity than slimmer girls because their bodies could potentially support a pregnancy. I'm not sure how much scientific research has been done on that, but I thought it was a pretty feasible hypothesis when we discussed it in class. I think that biology, social factors, chemical factors, and evolution all play a part in the maturation rate of girls

While future uncertainty may be an underlying cause, I think one's environment and education overrides it. Someone, I think, brought up the point that many of the teenage mothers do not consider teen pregnancy as much of an issue as some of us do, perhaps because of what they see around them (is teen pregnancy somewhat of a snowball effect?). I don't think that this phenomenon has to do with the lack of sexual education or availability of contraceptives, because there are many places, at least in cities, to obtain free contraceptives or pregnancy tests (for example, Planned Parenthood). In NYC, at least, sexual education is present in every curriculum and I'm pretty sure free condoms are readily available... This is all just to say that I don't think we can blame teen pregnancy on the lack of resources, as the future uncertainty theory says, but that we have to chalk it up to cultural influences pressures.

I believe that a socio-economic disadvantage is definately linked to teen pregnancy. Not only is there usually less parental involvement, which may lead the girl to feel that their are not many mates and so they must use whatever opportunities they get, but they also have a greater need for resources. Girls may intentionally get pregnant, thereby ensuring a male presence, which had been absent in childhood, or at least some economic resources. Also the lifespan is on average lower in socio-economic deprived regions. Thus, females have less time to reproduce, and so it may be important to start their sexual explorations earlier.

I believe that a socio-economic disadvantage is definately linked to teen pregnancy. Not only is there usually less parental involvement, which may lead the girl to feel that their are not many mates and so they must use whatever opportunities they get, but they also have a greater need for resources. Girls may intentionally get pregnant, thereby ensuring a male presence, which had been absent in childhood, or at least some economic resources. Also the lifespan is on average lower in socio-economic deprived regions. Thus, females have less time to reproduce, and so it may be important to start their sexual explorations earlier.

In my opinion, teen pregnancy is a result of a combination of factors, with biological signals being one of the least influential reasons. While the members of the lower class do deal with "future uncertainty" at a much high level than members of the middle and upper classes, it must also be considered that members of the lower class are not as widely educated about birth control and safe sex. In addition, members of the middle and upper classes are more likely to grow up with a certain set of morals impressed upon them by their elders and by a general sense of rejection toward teen pregnancy in the community. It seems that a pregnant teen living in a respectable neighborhood is more likely to be ashamed of herself than a young woman in the inner city who has been exposed to teen pregnancy throughout childhood and may not consider it as serious an issue.

In reference to early menarche, recent studies have concluded that the presence of chemicals and other artificial materials throughout daily life have contributed to menarche at an earlier age. While this is certainly not the only cause of earlier menarche, I do believe it is significantly responsible. However, stress is capable of doing serious and terrible things to the human body, and it is certainly feasible that "future uncertainty" would contribute to menstration beginning at a younger age, especially for females who grow up in households without a father.

Thus, while certain biological and evoluationary signals may be at work to contribute to earlier menarche and teen pregnancy, I do not believe that these signals are the main reasons why we see these phenomena.

One thing to consider here is that girls aren't wired with "future uncertainty" detectors that cause menarche to kick in when things start getting dicey.

The question then is, what signals DO the bodies of girls receive from the environment that would lead to this early menarche.

Try this: go search through psychinfo (accessible from the library webpage), and type in the terms "early and menarche and predictor". The studies all hit home on the same theme: turbulent childhoods (i.e., harsh/controlling mothers, absent fathers or presence of a stepfather, etc). By comparison, girls raised in stable/nurturing evirons reach menarche later.

Unfortunately, the food additives theory is basically untestable here in America, because we all eat the same crap, so there's no comparison group. The only comparison that could be done would be to compare typical american girls to Penn. Dutch Amish, but those cultures are too different to allow for any conclusions to be made. I only seem to be ranting b/c I love this stuff!

While evolution may play a role in early menarche, I have heard from my doctor and other medical professionals that girls are getting their first periods earlier and earlier because our food is more chemically treated now than in any other era. While it may not explain every case of early menarche, I feel like this is a much more valid explanation than "future uncertainty."

It is probably impossible because of a lack of data, but it would be very interesting to research throughout history and see if girls with absent fathers have consistently reached menarche before their peers with nuclear families. If they always have, then it would certainly back up "future uncertainty." However, if it does not, it would give the theory less credibility.

I don’t think that early menarche can be wholly chocked to “future uncertainty” as it is not just those girls raised in stressful situations that are getting their periods early. On a whole, girls are maturing earlier, and that includes those girls that are raised in loving, supportive families as well as those girls that grow up in unstable environments. Stress probably plays a part, but I believe that there is something more universal at play here.

The fact that girls are maturing faster makes early pregnancies more likely, but the relationship is more convenient for pregnancies than the cause of pregnancies. One only has to turn on daytime television to witness this. Jerry Springer and Maury oft tell tales of young girls whose only ambition in life is to become pregnant and have a child of their own, often following in their mother’s footsteps in getting pregnant early and often times raising a child without the help of the father. True, most of the time these pregnancies are unplanned, but I feel like the risk of pregnancy is approached recklessly, with an attitude of whatever happens happens. They are not consciously trying to get pregnant, but at the same time, they are more than willing and able to live with the consequences if they do. I believe that these early teen pregnancies are a result of the culture in which they were raised, and not a direct result of the stress in which they live.

I think it makes a lot of sense that girls reach reproductive maturity faster than boys. Women have a much shorter reproductive life span than men, and offspring generally receive significantly more parental investment from the mother. Therefore it is logical that they would mature first. Women also have a tendency, stereotypically/historically, to marry older men. Reaching sexual maturity first allows them to be reproductively viable for older men sooner, giving them more time to perpetuate their gene pools.
It would be interesting to investigate whether the offspring of many generations of successful individuals reached menarche later than those born into generations of lower income settings/poverty. This would indicate whether early menarche results from “future uncertainty.”
I think that earlier menarche is not a biological signal to start reproduction earlier. I think that teen pregnancies are purely cultural phenomena. I feel that girls raised in secure environments are taught from an early age that they have bright futures and sexual promiscuity and carelessness could compromise that. Girls from lower income families may not be told they have bright futures that they need to protect, and consequentially make poor choices.

Let's pull teen pregnancy out of the equation, as early menarche is a phenomenon that may be completely uncorrelated with teen pregnancy. That is, girls are having their first periods earlier, and this may have no bearing on teen pregnancy?

We know that there are potentially many factors influencing teen pregnancy, because having sex is a voluntary (usually) behavior. But, having your period is not a voluntary behavior and thus there should be fewer factors influencing this process.

I think that the idea of future uncertainty could play a role in the higher rates of pregnancy among teens who are at a socio-economic disadvantage or seem like they might not have a bright future for some other reason. Evolutionarily this makes sense, but I agree that in this case, cultural factors are most likely the overwhelming influence involved in teen pregancies. To account for cultural factors such as access to education and birth control, I think it would be more accurate in determining the envolutionary influence to look at the age of menarche, rather than pregnancy rates.

While I believe that future uncertainty may have some relation to unplanned teenage pregnancies, I feel like cultural and nurture plays a much larger role in whether a teenage girl becomes pregnant. I agree with Catherine when she says that lower income, urban teenagers probably cannot afford effective birth control measures, nor do they have much access to quality sex education. Similarly, teenage girls with absent fathers probably have unstable home lives, and they may feel like the only way they can be accepted by their peers is to be sexually active. While this evolutionary adaptation may play a role, I think it is a very subtle undercurrent that may only manifest itself if many other factors are at play.

I think that the evolutionary argument about future uncertainty makes sense, but I also think that there are definitely some other factors at play. Teen moms in low income urban settings might be less educated than women elsewhere and would probably have less resources,so they might therefore not have knowledge of or access to the various methods of birth control that are frequently used by other women. Also, these women may not have been taught about sex and the repercussions of sex as well as women from other areas. Overall, I think that many of the teen pregnancies in these areas are unplanned and unwanted. This goes along with the fact that teen mothers abandon their babies more frequently than older women with more resources.
Also, I think the stress factor has a few different angles from which it can be viewed. While it is possible that the stress of the environment leads to early menarche because of future uncertainty, the K&L article (pg. 189) discussed the fact that stress can also lead to decreased fertility.
Overall, I can definitely imagine a teen mother giving birth at a young age to fend off that fact that she may not live into old age, but I don't think that this is the only factor at play.