Do we know why girls are starting to mature physically at a younger age?

Genetics provide a window during which maturation occurs, but environmental and physical factors appear to influence the timing inside those parameters. For example, as the quality of nutrition and general health improve for children in a population, puberty tends to occur at earlier ages. The most interesting finding to date, however, has revealed a significant link between family cohesion and the onset of sexual development. Specifically, girls who have close, positive relationships with their fathers tend to mature later than those whose dads are cold, distant, and uninvolved.

Investigators at Vanderbilt University studied 173 girls and their families for eight years and drew that striking conclusion. Their findings were reported in the Journal of Personality and Social Psychology:¹

Researchers found that a father’s presence in the home, more time spent by fathers in child care, greater supportiveness in the parental dyad, more father-daughter affection, and more mother-daughter affection, as assessed prior to kindergarten, each predicted later pubertal timing by daughters in 7th grade. In summary, the quality of fathers’ investment in the family was the most important feature of the family environment relative to daughters’ pubertal timing.²

The Vanderbilt study has been replicated numerous times, including an investigation conducted in the United States and New Zealand.³ Researchers drew similar conclusions:

[Bruce Ellis, et al,] found that daughters from homes in which the biological father was present tended to experience puberty and their first sexual encounter at a later age than those whose father was absent. The closer and more affectionate the father-daughter relationship, the later the child’s sexual development occurred. A supportive relationship between parents delayed puberty still further. In contrast, the biological father’s absence, or friction between parents, was associated with earlier puberty, sexual activity and pregnancy…This effect was magnified by the presence of a stepfather: the more prolonged a girl’s exposure to a stepfather or mother’s boyfriend, the greater the chance of early puberty. . . .

The study clearly shows that stressful family relationships and the absence of a girl’s father are each independently associated with earlier timing of puberty in daughters, both having a similar impact. Ellis suggests that girls “detect and internally encode” information about the quality of their relationship with their fathers, and that this calibrates the timing of their reproductive development and sexual behavior in adolescence.⁴

There are other factors at work in the trend toward earlier maturation. It is believed that obesity and the distribution of fat are implicated. Furthermore, the onset of puberty appears to have declined because of the presence of estrogen in the environment, perhaps from exposure to discarded birth control pills and hormones in meat and dairy products. Other scientists suggest that pesticides and other chemicals that have qualities like estrogen may play a role.⁵

Finally, the onset of puberty is related to race. African American girls develop earlier than white girls, by twelve to eighteen months on average. The beginnings of breast development occur on average at 8.9 years for African American girls and 10.0 for white girls. Forty-eight percent of African American girls and 15 percent of white girls are showing clear signs of puberty by age nine.⁶

Footnotes:

1. B. J. Ellis, S. McFadyen-Ketchum, K. A. Dodge, G. S. Pettit, and J. E. Bates, “Quality of Early Family Relationships and Individual Differences in the Timing of Pubertal Maturation in Girls: A Longitudinal Test of an Evolutionary Model,” Journal of Personality and Social Psychology 77 (1999): 387–401.
2. “Father-Daughter Relationship Crucial to When Girls Enter Puberty, Researchers Say,” Science Daily (September 27, 1999); see http://www.sciencedaily.com/releases/1999/09/990927064822 .htm.
3. B. Ellis, J. Bates, K. Dodge, D. Fergusson, J. Horwood, G. Pettit, and L. Woodward, “Does Father Absence Place Daughters at Special Risk for Early Sexual Activity and Teenage Pregnancy?” Child Development 74 (2003): 801–821.
4. Mairi Macleod, “Her Father’s Daughter,” New Scientist (February 10, 2007): 38–41.
5. Diana Zuckerman, “When Little Girls Become Women: Early Onset of Puberty in Girls,” National Research Center for Women and Families; article first appeared in The Ribbon, a newsletter of the Cornell University Program on Breast Cancer and Environmental Risk Factors (BCERF) 6, no. 1 (Winter 2001).
6. Ibid.