Showing posts with label pubertal timing. Show all posts
Showing posts with label pubertal timing. Show all posts

Saturday, June 20, 2015

Gender reassignment of children. Does it really help?


"Flower boy" (on the right) - In 70-80% of cases, gender confusion will clear up on its own (Wikicommons: Recoplado).

 

I remember feeling some attraction to girls in Grade 2, but it really wasn't until Grade 8 that everything fell into place. I'm talking about puberty. Before high school, I was a boy and not a young man.

I didn't consider myself abnormal. Yes, many boys in Grade 8 had deeper voices, as well as signs of facial hair, but just as many did not, and a few would not have been "sexually functional." As for the earlier grades, certainly before Grade 7, most of us could have passed for little girls—just change the clothing, the hairstyle, and voilà!

Today, puberty is starting earlier. Ontario schools will begin explaining it in ... Grade 4. This falling age is largely due to the changing ethnic and racial origins of the student population, as well as things like overeating (in the case of girls) and perhaps our more sexualized culture.

Nonetheless, a lot of boys remain pre-pubertal throughout most of primary school, and some may have trouble coming to terms with their male identity. They experience what is called “gender confusion.” This is hardly surprising. Testosterone levels are low before puberty, and some boys, especially the ones who have been less androgenized in the womb, may genuinely feel like a girl. I also suspect that modern culture makes things worse by creating expectations that even adult males have trouble meeting. Go to any fitness center and you'll see plenty of young men trying to bring their bodies into line with the "rippled look."

Gender confusion, known medically as gender identity disorder, affects children of both sexes but boys much more so, at least in North America. One clinic reported a ratio of 6.6 boys for each girl, the sex imbalance being attributed partly to greater intolerance of feminine behavior in boys (Zucker et al., 1997). This disorder seems to be partly heritable, although we face a similar problem of perspective here as with the referral statistics (Heylens et al., 2012). To what degree does the heritable component reside in how these children objectively behave, and not in one behavior that may or may not alarm another person, usually a parent? In practice, it’s the latter. It’s whatever behavior that makes a parent bring the child to a clinician’s office.

Gender reassignment

We now come to the issue of medical treatment, specifically "gender reassignment." This treatment has recently been condemned by Dr. Paul McHugh, the former psychiatrist-in-chief for Johns Hopkins Hospital:

Then there is the subgroup of very young, often prepubescent children who notice distinct sex roles in the culture and, exploring how they fit in, begin imitating the opposite sex. Misguided doctors at medical centers including Boston's Children's Hospital have begun trying to treat this behavior by administering puberty-delaying hormones to render later sex-change surgeries less onerous—even though the drugs stunt the children's growth and risk causing sterility. (McHugh, 2015)

Is treatment really necessary? McHugh points out: "When children who reported transgender feelings were tracked without medical or surgical treatment at both Vanderbilt University and London's Portman Clinic, 70%-80% of them spontaneously lost those feelings."

McHugh has been accused by the transgender community of misrepresenting the facts:

McHugh also mischaracterizes the treatment of gender nonconforming children. As McHugh states, most gender nonconforming children do not identify as transgender in adulthood.  However, those who receive puberty blocking drugs do not do so until puberty, when trans identity is likely to persist. These drugs allow adolescents and their parents to work with doctors to achieve the best outcome. This approach was demonstrated to be successful in research in the Netherlands before being adopted widely in the U.S. (WPATH, 2015) 

The above text is disingenuous in two ways. First, puberty-blocking drugs are not administered until puberty for an obvious reason: they would be ineffective earlier. The decision to use them, however, is made at an earlier time and often much earlier. Second, these drugs keep hormonal levels from rising, thus maintaining the boy or girl in the same hormonal state and possibly in the same state of gender confusion. Logically, one should wait a few years to see what effect puberty might have.

Is the use of these drugs legitimate? We’re talking about a radical intervention in the normal process of maturation, and this intervention begins before the age of consent, i.e., 16 years of age in most Western countries. Moreover, the eventual gender reassignment will never be complete. Although it’s possible to turn a male into a semblance of a female, such a “female” can never bear children. This isn’t a minor point, given that many male transsexuals wish to maintain a male heterosexual orientation, even to the point of marrying and becoming fathers.

For all these reasons, use of these drugs should be delayed until adulthood, when consent becomes morally defendable, when the risks of sterility are lower, and when the gender confusion may prove to be transitory.

A boy is not a little man

The transgender community likes to talk a good talk about "gender fluidity." Ironically, such fluidity is reduced by gender reassignment, which imposes a relatively unchanging adult dichotomy on pre-pubertal individuals who are going through rapid physical and psychological change. This brings us to a second irony. The transgender community complains about how it was once medically pathologized. Yet here it is pathologizing cases of gender confusion that are not unusual among young children and that are consistent with normal child development.

We should remember that both sexes begin with a body plan that is more female than male. This plan is modified at two points of the life cycle: first, in the womb, when the body’s tissues are primed by a surge of androgens or estrogens; and then at puberty, when boys and girls diverge in the levels of their circulating sex hormones, which in turn trigger profound changes in growth and development.

This truth was known to our ancestors. As late as the early 20th century, people accepted that little boys are more akin to little girls than to grown men. This was why both sexes would be dressed in female clothing until school age, and a mother would often boast that her little boy was as pretty as a girl.

[…] infants and small children had for hundreds of years been dressed alike, in frocks, so that family portraits from previous centuries made it difficult to tell the young boys from the girls. “Breeching,” as a rite of passage, was a sartorial definition of maleness and incipient adulthood, as, in later periods, was the all-important move from short pants to long. Gender differentiation grew increasingly desirable to parents as time went on. By the closing years of the twentieth century the sight of little boys in frilly dresses has become unusual and somewhat risible; a childhood photograph of macho author Ernest Hemingway, aged almost two, in a white dress and large hat festooned with flowers, was itself the focus of much amused critical commentary when reproduced in a best-selling biography—especially when it was disclosed that Hemingway’s mother had labelled the photograph of her son “summer girl.”  (Garber, 1997, pp. 1-2)

Hemingway hated those baby pictures, as well as the stories about how his mother would call him “Ernestine” and tell strangers that he and his sister were twin girls. During her declining years, he threatened to cut off his financial support if she ever gave an interview about his childhood (Onion, 2013; Winer, 2008). He saw her as the typical Victorian mother who sought to momify and symbolically castrate her male offspring. With other writers of his time, particularly psychologists and advice columnists, he helped bring about a reform of sexual conventions that, among other things, would sweep away the custom of cross-dressing little boys.

(see here for an early childhood photo of Hemingway and here for similar photos of H.P. Lovecraft

I remember how I felt seeing such photos when doing research on my family tree. What the?? Today, I feel differently: this cross-dressing strikes me as being healthy, even beautiful in its own way. It avoids the problem of imposing male identity too early in life and thereby forcing slower-developing boys to choose between the identity imposed by society and the one generated by their own mental state—which may still be insufficiently male. It is this situation, and the resulting gender confusion, that is now putting many boys at risk of gender reassignment. Yet there’s nothing wrong with most of them. They just need more time to grow up.

As an extreme example, let’s take the case of "pseudohermaphrodites"—males who look female at birth because their penis resembles a clitoris and because their testes remain inside the body. They are typically raised as girls until puberty, at which time the penis grows in size, the testes descend into the scrotum, and they become like men physically and psychologically. When 18 pseudohermaphrodites were studied in the Dominican Republic, it was found that 16 of them had made the transition from girlhood to manhood with no evidence of psychosexual maladjustment (Imperato-Mcginley et al., 1979). A similar situation often arose among Canada’s Inuit whenever a newborn received the name of a deceased relative. If the child was a boy and the relative a woman, it would be raised as a girl until puberty and as a man thereafter. Such individuals became not only husbands and fathers but also respected shamans (Saladin d'Anglure, 2005).

In short, gender confusion in childhood poses no threat to normal child development. Indeed, whether we acknowledge it or not, all boys start off being more like little girls than the men they will become. This “early girlhood” may actually play a key role in their psychosexual development, and our ancestors might have had good reasons to believe that boyhood begins later. But that raises a troubling question: by trying to masculinize this early phase of life, have we opened the door to unknown consequences?

So if you have a young boy who’s confused about his gender identity, the chances are very good that he’ll successfully transition to manhood ... as long as he’s not given puberty-blocking drugs. This is not a medical condition that needs treatment.

References 

Garber, M.B. (1997). Vested Interests: Cross-Dressing and Cultural Anxiety, Psychology Press.
https://books.google.ca/books?id=eeASHasS0oUC&printsec=frontcover&hl=fr&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false 

Heylens, G., G. De Cuypere, K.J. Zucker, C. Schelfaut, E.Elaut, H. Vanden Bossche, E. De Baere, and G. T’Sjoen. (2012). Gender identity disorder in twins: A review of the case report literature, The Journal of Sexual Medicine, 9, 751-757.
http://onlinelibrary.wiley.com/doi/10.1111/j.1743-6109.2011.02567.x/abstract 

Imperato-Mcginley, J., R.E. Petersen, T. Gautier, and E. Sturia. (1979). Male pseudohermaphroditism secondary to 5a-reductase deficiency—A model for the role of androgens in both the development of the male phenotype and the evolution of a male gender identity, Journal of Steroid Biochemistry, 11, 637-645.
http://www.sciencedirect.com/science/article/pii/0022473179900931 

McHugh, P. (2015). Transgender surgery isn't the solution, The Wall Street Journal, June 12
http://www.wsj.com/articles/paul-mchugh-transgender-surgery-isnt-the-solution-1402615120 

Onion, R. (2013). Pages from Hemingway’s baby books, Slate, July 23
http://www.slate.com/blogs/the_vault/2013/07/23/hemingway_scrapbooks_grace_hemingway_s_records_of_son_ernest_hemingway_s.html  

Saladin d'Anglure, B. (2005). The 'Third Gender' of the Inuit, Diogenes, 52, 134-144.
http://dio.sagepub.com/content/52/4/134.short 

Winer, A. (2008). Why Hemingway used to wear women’s clothing, Mental_floss, December 18
http://mentalfloss.com/article/20396/why-hemingway-used-wear-womens-clothing 

WPATH (2015). Wall Street Journal Editorial Critiques Transgender Health July 2, 2014
http://www.wpath.org/site_page.cfm?pk_association_webpage_menu=1635&pk_association_webpage=4905 

Zucker, K.J., S.J. Bradley, and M. Sanikhani. (1997). Sex differences in referral rates of children with gender identity disorder: some hypotheses, Journal of Abnormal Child Psychology, 25, 217-227.
http://link.springer.com/article/10.1023/A:1025748032640#page-1

Saturday, February 9, 2013

Why are girls and boys maturing earlier?


For girls, the age of puberty has been falling since the 19th century. The same period has seen a similar decline for boys (source)


In the United States and other Western countries, girls have been reaching puberty at earlier and earlier ages. A recent longitudinal study has examined this trend in white Americans born between 1928 and 1992. Its conclusion? Girls are reaching puberty earlier because of an interaction between a lifestyle factor and a pre-existing genetic predisposition:

Our data also show, for the first time, that the effect of menarche SNPs on prepubertal BMI was stronger in children born more recently compared to those born earlier in the century, thereby suggesting that the developmental genetic susceptibility to elevated BMI may have only been ''uncovered'' in the more obesogenic environments of the recent past. (Johnson et al., 2013)

For the study's authors, the lifestyle factor is that girls are eating more, exercising less, and accumulating more body fat. Because fatty tissue is a significant source of estrogen, an increasing percentage of body fat tends to hasten puberty in young girls (Frisch & Revelle, 1970; Frisch & McArthur, 1974; Kaplowitz et al., 2001; Siiteri & MacDonald, 1973). This effect is stronger in girls with a certain genetic background:

It is possible that over the examined time period, individuals with higher genetic burden for accelerated sexual development are for the first time ''allowed'' by liberalization of the environment to alter dietary intake and energy expenditure to support their genetic potential for rapid weight gain and earlier sexual development. (Johnson et al., 2013)

But why are boys too maturing earlier?

In boys, body fat is not linked to early puberty. In fact, there seems to be a negative correlation, perhaps because fatty tissue is a significant source of estrogen (Wang, 2002). Overweight boys often present signs of disrupted male sexual development, e.g., breast budding, higher voice pitch, etc.

Yet boys likewise are reaching puberty at an earlier age. This is the conclusion of a recent American study:

We observed that onset of secondary sexual characteristics in US boys as seen in office practice appears to occur earlier than in previous US studies and the 1969 British study commonly used for pubertal norms. […] White boys in our study entered stage 2 genital growth 1.5 years earlier than the British boys (10.14 vs 11.60 years of age).

[…] These data are consistent with recent trends from other countries, such as Denmark, Sweden, Great Britain, Italy, and China. For example, urban Han Chinese boys achieve a testicular volume of ≥4 mL (13% by age 9) and spermarche earlier than studies conducted several decades ago; Danish boys achieve a testicular volume >3 mL more than 3 months earlier now than 15 years ago. (Herman-Giddens, 2012)

This trend has also been observed in the age when a boy's voice begins to change:

According to records kept by the Leipzig choir, the most common period of voice breaking for male singers in the mid-18th century was between 17.5 and 18.5 years of age (Daw, 1970); in contrast, children enrolled in the Copenhagen Municipal Choir School from 1994-2003 had a median age of voice breaking of 10.4 years (Juul, Magnusdottir, Scheike, Prytz, & Skakkebæk, 2007), which is consistent with the choir's subjective reports of difficulty retaining children as singers past the age of 12 or 13 years. (Mendle & Ferrero, 2012).

This is a challenge for Occam's Razor, and the task is no easier if we look at other possible causes. If the cause isn’t a higher proportion of body fat, could it be a higher level of estrogens and estrogen-like substances in the environment? (see earlier post). Yes, that might hasten puberty in girls and increase accumulation of body fat. But in boys it would delay puberty by offsetting the rising level of male hormones.

In trying to figure out the causal chain of events, we should keep in mind that the relationship between body fat and age of puberty runs in both directions. On the one hand, estrogen from body fat lowers the age of puberty in girls. On the other hand, earlier puberty increases ovarian production of estrogen, which in turn stimulates deposition of body fat, particularly on the hips, buttocks, and breasts (Van Lenthe et al., 1996). So perhaps some unknown factor is causing earlier sexual development in both sexes and thus greater deposition of body fat in girls.

A response to social cues?

This unknown factor might be something in the social environment. As Hawley (2011) argues, humans unconsciously monitor their social environment for reproductive opportunities and accordingly speed up or slow down their pace of sexual development:

[...] human children, especially girls, may be sensitive to their early socioecological conditions in ways that entrain development toward either a faster (earlier pubertal maturation, more sexual partners, less stable relationships) or slower (later pubertal maturation, fewer sexual partners, more stable relationships) life history strategy.

With the transition to post-traditional societies, there has been an increase in the erotic stimuli that preteens encounter in their surroundings:

Common in traditional societies are adult-supervised adolescent initiation ceremonies (Schlegel & Barry, 1980) that are designed to commemorate the transition from childhood to adulthood and inculcate the adolescent with adult values, duties, behaviors, and sex roles associated with the culture (Schlegel, 1973). That is, these adolescents are taught adult sex roles by adults. We now appear to have a complete turnaround. In modern, Western cultures, adolescents derive sexual relationship expectations from television, cable, music, purveyors of racy lingerie (who target teenage girls), and pornography that they can now access on the Internet and thereby carry around on their cell phones. (Hawley, 2011)

Erotic imagery in particular is today available to a degree that was impossible not so long ago. Young boys and girls have virtual access to an endless supply of picture-perfect sexual partners. Whatever the media—films, TV, magazines, the Internet—we're exposed to images that can stimulate sexual desire as efficiently as what normally exists in the real world. More so, in fact. These images are ‘supernormal’ stimuli.

To date, only one study has looked into possible relationships between erotic imagery and pubertal timing:

The aim of this study was to investigate associations between pubertal timing and boys' Internet use, particularly their viewing of pornography. We used a sample comprising of 97 boys in grade 8 (M age, 14.22 years) from two schools in a medium-sized Swedish town. This age should be optimal for differentiating early, on-time, and later-maturing boys. Boys responded to self-report questionnaires on their Internet use and pubertal timing. Early, on-time, and late-maturing boys did not differ in terms of most Internet activities. However, early maturers reported downloading and viewing pornography more often than the other boys did (p<.001). (Skoog et al.,2009)

Admittedly, the arrow of causality might point in the other direction, i.e., early maturing boys have a stronger sex drive and thus a greater interest in porn. This was, in fact, the authors' explanation. We should also remember the well established correlation between early puberty in girls and the absence of a father in the home. It was long thought that father absence triggers early puberty in girls. In fact, a twin study has shown a genetic cause: absent fathers tend to have genes that favor earlier sexual development in their progeny (Mendle et al., 2006).

One might also object that the decline in the age of puberty began long before the Internet. Before the Internet, however, there were porn magazines. And before them, there were pictures garnered from art books, fashion magazines, or the lingerie sections of mail-order catalogues. One could also bring erotic images to mind by reading certain novels. Thus, modern pornography is merely the latest stage of a lengthy co-evolution between, on the one hand, improvements in photography and other imaging technologies and, on the other hand, a weakening of taboos against masturbation. At the beginning of this co-evolution, in the 19th century, masturbation was much less developed among young boys and girls as a sexual lifestyle. Visual aids were scarce and of poor quality, religious injunctions were strong, and adult supervision inside and outside the home was omnipresent.

Conclusion

The age of puberty might be declining because boys and girls are being exposed to ever more and ever better erotic imagery, but this hypothesis needs confirmation by longitudinal studies to determine which is the cause and which is the effect. Another drawback with current research is its focus on the most extreme forms of pornography, such as child porn. Yet the usual stuff is the kind that most people consume ... and in unparalleled quantities. As the authors of a recent Dutch study remarked:

[...] we can only emphasize that Dutch youth are confronted with and expose themselves to an unprecedented amount of R-rated and Xrated material in the media. Research on its consequences for adolescents' sexual socialization is largely missing but, as this study has shown, is urgently needed. (Peter & Valkenberg, 2006)

And erotic imagery isn't confined to X-rated websites or magazines. It is in fact ubiquitous in modern social environments. Girls might accelerate their sexual development by leafing through fashion magazines just as boys might accelerate theirs by viewing porn.

The erotic imagery hypothesis will have to fit the data better than rival hypotheses. Two of these, the body fat and environmental estrogen hypotheses, can explain the decline in the age of puberty for girls but not for boys. Another possible cause is better nutrition. Yet, among white Americans at least, much of this decline has happened since the 1950s—when nutrient levels were already adequate for this population. Finally, there is the possibility that puberty is happening earlier because genes that favor that developmental trajectory are spreading within the population. Modern social environments favor a reproductive strategy of early puberty, low parental investment and, especially, low paternal investment—in short, the ‘cads’ are outbreeding the ‘dads’ (see earlier post).

References

Frisch, R.E., R. Revelle. (1970). Height and weight at menarche and a hypothesis of critical body weights and adolescent events, Science, 169, 397-399.

Frisch, R.E. & J.W. McArthur. (1974). Menstrual cycles: fatness as a determinant of minimum weight necessary for maintenance or onset, Science, 185, 949-951.

Hawley, P.H. (2011). The evolution of adolescence and the adolescence of evolution: The coming of age of humans and the theory about the forces that made them, Journal of Research on Adolescence, 21, 307-316.
http://www.people.ku.edu/~phawley/Publications/Hawley%202011%20JRA%20Evo%20of%20Adol.pdf

Herman-Giddens, M.E., J. Steffes, D. Harris, E. Slora, M. Hussey, S.A. Dowshen, R. Wasserman, J.R. Serwint, L. Smitherman, & E.O. Reiter. (2012). Secondary sexual characteristics in boys: Data from the Pediatric Research in Office Settings Network, Pediatrics, 130, e1058-e1068.
http://pediatrics.aappublications.org/content/130/5/e1058.full.pdf+html

Johnson, W., A.C. Choh, J.E. Curran, S.A. Czerwinski, C. Bellis, T.D. Dyer, J. Blangero, B. Towne, & E.W. Demerath. (2013). Genetic risk for earlier menarche also influences peripubertal body mass index, American Journal of Physical Anthropology, 150, 10-20

Kaplowitz, P.B., E.J. Slora, R.C. Wasserman, S.E. Pedlow & M.E. Herman-Giddens. (2001). Earlier onset of puberty in girls: relation to increased body mass index and race, Pediatrics, 108, 347-353.

Mendle, J. & J. Ferrero. (2012). Detrimental psychological outcomes associated with pubertal timing in adolescent boys, Developmental Review, 32, 49-66.

Mendle, J., E. Turkheimer, B.M. D'Onofrio, S.K. Lynch, R.E. Emery, W.S. Slutske, N.G. Martin. (2006). Family structure and age at menarche: a children-of-twins approach, Developmental Psycholpgy, 42, 533-542.

Peter, J. & P.M. Valkenberg. (2006). Adolescents' exposure to sexually explicit material on the Internet, Communication Research, 33, 178-204.

Siiteri, P.K. & P.C. MacDonald. (1973). Role of extraglandular estrogen in human endocrinology. In S.R. Geiger (ed.), Handbook of Physiology, Washington D.C. American Physiology Society, sect. 7, vol. 2, part 1, pp. 615-629.

Skoog, T., H. Stattin, & M. Kerr. (2009). The role of pubertal timing in what adolescent boys do online, Journal of Research on Adolescence, 19, 1-7.

Van Lenthe, F.J., C.G. Kemper & W. van Mechelen. (1996). Rapid maturation in adolescence results in greater obesity in adulthood: the Amsterdam Growth and Health Study, American Journal of Clinical Nutrition, 64, 18-24.

Wang, Y. (2002).Is obesity associated with early sexual maturation? A comparison of the association in American boys versus girls, Pediatrics, 110, 903-910.

Saturday, November 3, 2012

Are the cads outbreeding the dads?

Whom will she choose? (source)
 
There has been much talk about two findings from a recent study: (a) boys reach puberty at different ages in different ethnic groups and (b) boys are reaching puberty earlier now than in the recent past.

The first finding is in line with previous studies:

[…] we found significant differences in the age of onset of stage 2 genital and pubic hair growth between African American boys as compared with white and Hispanic boys and transition to testicular volumes ≥4 mL (but not 3 mL). The meaning of this finding is unclear, as no existing studies inform differences in mean testicular size at given ages, by race/ethnicity, and sexual maturity stage; or in racial/ethnic differences in the rate of advancement through the Tanner stages over time. (Herman-Giddens, 2012)

The second finding is new:

We observed that onset of secondary sexual characteristics in US boys as seen in office practice appears to occur earlier than in previous US studies and the 1969 British study commonly used for pubertal norms. […] White boys in our study entered stage 2 genital growth 1.5 years earlier than the British boys (10.14 vs 11.60 years of age).
 
[…] These data are consistent with recent trends from other countries, such as Denmark, Sweden, Great Britain, Italy, and China. For example, urban Han Chinese boys achieve a testicular volume of ≥4 mL (13% by age 9) and spermarche earlier than studies conducted several decades ago; Danish boys achieve a testicular volume  ≥3 mL more than 3 months earlier now than 15 years ago. (Herman-Giddens, 2012)

The authors put the cause down to “exposure to chemicals, changes in diet, less physical activity, and other modern lifestyle changes and exposures.” In an article for CNN, the lead author elaborated:
 
"The changes are too fast," Herman-Giddes said. "Genetics take maybe hundreds, thousands of years. You have to look at something in the environment. That would include everything from (a lack of) exercise to junk food to TV to chemicals." (Wilson, 2012)

Yes, new genetic variants take time to appear through mutation. But variants for early puberty already exist in the population. Natural selection has only one thing to do: increase the proportion of people with those variants. And that can happen with each passing generation.

In any given population, almost all variability in male pubertal timing is genetic. This was the conclusion of a Swedish twin study: 

The heritability was 0.91 for age at onset of growth spurt and 0.93 for age at peak height velocity in this Swedish cohort of male twin pairs. Of interest is that these heritability estimates are almost the same as those reported from a Belgian twin study; that is, 0.93 and 0.92, respectively. Lower heritability estimates, 0.49 and 0.74, respectively, were found in a Polish twin study. (Silventoinen et al., 2008)

There is thus plenty of genetic variation for selection to act on. No need to wait for new mutations. But why would there be natural selection for earlier male puberty?

One reason is that early puberty is genetically linked to other sexual characteristics. In particular, a class of X-linked androgen receptor alleles is linked in males to aggression, impulsivity, sexual compulsivity, and lifetime number of sex partners and in females to paternal divorce, father absence, and early menarche (Comings et al., 2002). It is likely that these alleles also influence male pubertal timing, but research on this point is lacking—apparently because it is difficult to find a marker for pubertal maturation among boys that is as salient as age at menarche among girls (Ge et al., 2007). Early male puberty thus seems to be part of a “package,” or more precisely a reproductive strategy, that affects the way men go about finding a mate. Natural selection may favor one strategy or another, depending on the current cultural environment.

Is natural selection now favoring the “cads” over the “dads”? That might be what’s happening. As sexual relationships become less stable and shorter-term, women will ignore men who are oriented towards stable, long-term relationships.  This was the conclusion of a study directed by Kruger et al. (2003) at the University of Michigan's Institute for Social Research:

In the study, 257 women in college were asked to read passages from Scott's novels. Each read a paragraph describing a dark hero and one describing a proper hero. Then the women were asked which type of man they would prefer for a relationship.
 
As predicted by the cad-dad theory of human mating strategies, the women preferred the proper heroes for long-term unions. When asked which character they would like to see their future daughters choose, they also selected proper heroes. But when asked who appealed to them most for short-term affairs, the women turned to the dark heroes: the handsome, passionate and daring cads (Duenwald, 2003).

References

Comings, D.E., D. Muhleman, J.P. Johnson, & J.P. MacMurray. (2002). Parent-daughter transmission of the androgen receptor gene as an explanation of the effect of father absence on age of menarche. Child Development, 73, 1046-1051.
Duenwald, M. (2003). For a good time, well, don’t call dad, University of Nebraska-Lincoln, Anthropology, Raymond Hames
http://www.unl.edu/rhames/courses/current/dad-cad.htm

Ge, X., M.N. Natsuaki, J.M. Neiderhiser, & D. Reiss. (2007). Genetic and Environmental Influences on Pubertal Timing: Results From Two National Sibling Studies, Journal of Research on Adolescence, 17, 767–788.

Herman-Giddens, M.E., J. Steffes, D. Harris, E. Slora, M. Hussey, S.A. Dowshen, R. Wasserman, J.R. Serwint, L. Smitherman, & E.O. Reiter. (2012). Secondary sexual characteristics in boys: Data from the Pediatric Research in Office Settings Network, Pediatrics, 130, e1058-e1068.
http://pediatrics.aappublications.org/content/130/5/e1058.full.pdf+html

Kruger, D.J., M. Fisher, & I. Jobling. (2003). Proper and dark heroes as DADS and CADS. Alternative mating strategies in British Romantic literature, Human Nature, 14, 305-317.

Silventoinen, K., J. Haukka, L. Dunkel, P. Tynelius, & F. Rasmussen. (2008). Genetics of pubertal timing and its associations with relative weight in childhood and adult height: The Swedish Young Male Twins Study, Pediatrics, 121, e885-891
http://pediatrics.aappublications.org/content/121/4/e885.full.pdf+html

Wilson, J. (2012). Boys – like girls – hitting puberty earlier, October 23, CNN
http://edition.cnn.com/2012/10/20/health/boys-early-puberty/index.html