New research published in Evolution and Human Behavior has found that girls whose fathers were divorced started reproduction about 9.2 months earlier than girls whose fathers were no longer living.
Researchers have been interested in investigating why and how stressful experiences in childhood affect sexual maturation, behaviors, and reproductive outcomes. Girls who grow up without a father may start reproduction earlier because the absence is a cue of environmental harshness and uncertainty in which a fast life history strategy is favored. Alternatively, the trend might be the result of genetic factors.
Researchers Markus Valge and colleagues were interested in investigating whether the absence of the father, the mother, or both was most associated with the early onset of puberty among girls. The researchers used a large dataset to study girls who were born between 1936 and 1962 in Estonia. Valge and colleagues had access to information about the girls’ rate of puberty (via breast development stages), when they had their first child, and their overall reproductive success (how many children they had in their lifetime). The girls either grew up in orphanages, without a mother, or without a father due to either divorce or death.
After analyzing the data, the researchers found that girls whose fathers divorced started reproduction about 9.2 months earlier than girls who grew up with only their father or both parents present, and about 7.4 months earlier than girls whose fathers died. However, the difference in reproductive starting age was not significant once education was controlled for.
Girls whose mothers died had .25 less children in their lifetime on average than girls who grew up with just a mother or a father. There was no difference in the number of children girls had when their fathers died compared to girls who grew up in an orphanage.
This study indicates that stressful childhood environments do not predict faster sexual maturation for girls when controlling for education. Valge and colleagues argue this may be due to low test power and confounding variables. However, there was an association between how old the girls were when they had their first child and whether their parents were divorced. Valge and colleagues argue this could be explained by Flinn’s hypothesis that suggests fathers guard their daughters from predatory men, so girls with fathers in their life reproduce later in life.
However, this hypothesis is only partially supported because girls whose fathers were dead did not have children significantly earlier than girls whose fathers were present. Valge and colleagues argue that the Grandmother Hypothesis (in which mothers help promote the survival of their grandchildren) is supported, considering girls whose mothers died had .25 less children on average.
A limitation of this study is that there was no information regarding whether a step-parent was involved in the families in which mothers and fathers were absent. There was also a lack of information about the girls’ age when a parent died or divorced.
The study, “Pubertal maturation is independent of family structure but daughters of divorced (but not dead) fathers start reproduction earlier“, was authored by Markus Valge, Richard Meitern, and Peeter Hõrak.