Notably, adrenal puberty does not include breast development or the onset of menstruation for girls (or testicular enlargement, in the case of boys). The study posits that girls become mentally mature enough to care for their younger siblings while not being physically capable of having their own children, which would naturally draw them away from their older daughter responsibilities.
Older brothers are seemingly off the hook when it comes to this kind of parentification: The researchers did not find the same result in boys or daughters who were not first-born.
“One reason that we didn’t find this effect in first-born children who are sons could be that male children help less often with direct childcare than female children do, so mothers have less of an adaptive incentive to speed their social pubertal development,” Hahn-Holbrook explained.
Plus, she said, previous research suggests that female puberty timing is more malleable in response to early life experiences than males.
The results of this study, published in the February issue of Psychoneuroendocrinology (say that five times fast ― or just once), were a long time coming: Researchers tracked the families for 15 years, from the pregnancy stage to the babies’ teen years.
Researchers recruited women from two obstetric clinics in Southern California during routine first trimester prenatal care visits. On average, the women were 30 years of age and pregnant with one child, not twins.
It was their first pregnancy for roughly half of the participants. The women were nonsmoking and not using steroid medications, tobacco, alcohol or other recreational drugs during pregnancy. They were all over 18 years of age.
At five different stages of pregnancy, the women’s stress, depression and anxiety levels were measured, and then measured cumulatively. The depression assessment asked the women to rate the truth of statements such as “I felt lonely,” while the anxiety question asked how often they felt particular symptoms, such as “jittery.”
Of the children born to these mothers, 48% were female and 52% were male.
As the children aged, characteristics of adrenal and gonadal puberty were separately measured ― things like body hair, skin changes, growth in height or growth spurts, breast development and the onset of menstruation in females and voice changes and facial hair growth in males.
The study also measured childhood adversity to account for other factors known to correlate to early maturation or signs of puberty in children, like the death of a parent or divorce before age 5 and the absence of a father and economic uncertainties at ages 7–9.
Taking all that into account, it was the eldest girls who matured the fastest when their moms experienced high levels of prenatal stress.
Other studies suggest that there is some later-in-life payoff for highly responsible eldest girls: A 2014 study found that eldest daughters are the most likely to succeed out of any sibling type, while a 2012 study found that those who are eldest-born are more likely to hold leadership roles.
Source: https://www.buzzfeed.com/brittanywong/as-it-turns-out-eldest-daughter-syndrome-is-a-real-thing
