Ray Blanchard wrote a Letter to the Editor of the Archives of sexual behavior explaining why hebephilia is not an evolved behavior. I disagree with most of his statements and started pondering under which circumstances pedophilic behavior could have been beneficial. It is in this sense, i consider this behavior to be "normal". With pedophilic behavior i mean any long term relationship with someone younger than secondary sexual characteristics.
My guess is that the second brain size increase 800.000 years ago is related to an advance of tool making . It is not the toolmaking itself, but the transfer of that knowledge to the next generation that is interesting.
Rind&Yuill 2012 had the notion of mature-immature homosexual relationships, which combine apprenticeship and a temporary partnership. Vanggard in Phallos wrote about semen culture, where masculinity is transferred from the older to the younger partner. Since the evidence of such partnerships are spread over the world, it is a behavior which presumably is more than 50.000 years old.
Hence, if the tool makers in the early stone age did take an interest in eager, willing to learn boys, then it would have been an evolutionary advantage. I also reasoned that a longer apprenticeship would give the apprentice a higher standing and therefore a higher survival rate to his offspring. That means that this evolutionary pressure could have been at work until the introduction of public schools in recent history. The decline of the onset of puberty would support this hypothesis. Moreover, placing the pressure onto boys would also explain why boys mature later than girls.
I wrote a longer blog essay about that train of thoughts.