A girl whose biological father does not live in her household has a higher chance of entering puberty earlier than her peers, say researchers from the University of California, Berkeley ...The full study is here.
The age at which girls are reaching puberty has been trending downward in recent decades, but much of the attention has focused on increased body weight as the primary culprit. While overweight and obesity alter the timing of girls' puberty, those factors don't explain all of the variance in pubertal timing. The results from our study suggest that familial and contextual factors - independent of body mass index - have an important effect on girls' pubertal timing.
I should also note that there is another view about this research:
But in the end, the epidemic of earlier and earlier puberty is a myth that the media love and certain researchers continue to propagate. The tale's promotion doesn't always depend on data. Instead, worries about earlier physical maturation in girls sublimate and propel concerns about society's sexualization of young girls, whether by provocative dance routines or revealing clothing.Here is another medical news study that says that new moms suffer depression at about three times the rate of new dads. Dads are psychologically and emotionally stabilizing influences. This one should be obvious. A lot of new moms are mentally unstable.