Growing up as the oldest sibling, author Y. A University of California, Los Angeles-led research team found that, in certain instances, first-born daughters tend to mature earlier, enabling them to help their mother rear younger siblings. Specifically, the researchers found a correlation between early signs of adrenal puberty in first-born daughters and their mothers having experienced high levels of prenatal stress.
Why does age of adrenal puberty matter? Changes in skin acne, for instance and body hair happen during this phase, but so do changes in brain development. Adrenal puberty processes are believed to foster social and cognitive changes; basically, superficial physical changes correlate with emotional maturity. 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. Plus, she said, previous research suggests that female puberty timing is more malleable in response to early life experiences than males.
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. 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 7β9.
