Hmmm - I'm not sure on the conclusions, at least as their presented here. Though I do support genetics underpinning lots of things, I can't make the leap they do in the last paragraph. First, I think it's much more likely that the daughters learned from their mothers that bearing children later or earlier in life is better - depending on the mother. Secondly, from my limited understanding, childbirth does tend to have negative affects on a woman's health (depleted calcium, lowered energy levels, increased weight, etc.) that, because they have an earlier onset, could also be culprits...

note that the data is from pre antibiotic era. There are some suggestions that onset of menses was later in earlier eras because of relatively poor early nutrition. in other words, it took a long time for female physiques to build the reserves necessary to carry a pregnancy to term.