From this and the observed fact that girls seem to be starting puberty earlier than they used to, the authors conclude (or should I say hypothesize?) that lack of attachment caused the early puberty in the NICHHD girls. They further hypothesize that the species wide early puberty is caused by stress in the environment, which apparently causes animals to breed earlier.
"An evolutionary biology perspective says, 'look, the thing that nature most cares about -- with respect to all living things, humans included -- is dispersing genes in future generations,'" says Belsky. "Thus, under those conditions in which the future appears precarious, where I might not even survive long enough to breed tomorrow, then I should mature earlier so I can mate earlier before that precarious future might get me." This is the evolutionary logic, according to Belsky, which led to the prediction -- and now evidence -- that early insecurity should be related to earlier pubertal development.This sure seems fuzzy to me. Maybe it's the metaphorical language ("I should mature earlier") when I'm sure the actual researchers are probably thinking about epigenetic factors, some hormone released in the brains of insecure babies causes some genes to turn on early.
But the actual reasoning chain seems fuzzy to me, too. Something about being insecure at 15 months causes girls to start puberty earlier than other girls. Therefore this recent drop in age of puberty is caused by a species-wide insecurity in baby girls. The reason one group of girls starts puberty earlier than another group is the same reason average girls now go through puberty earlier than average girls used to. It just doesn't follow. It's interesting, and I'm glad they did it, and we can probably learn something useful from it, but I don't see how the big step follows.