I can't find the article now, but an evolutionary-psychology noticed that the "cooties" concept seems to exist across all cultures (though obviously not always given the name "cooties"), and furthermore noticed that children often don't consider their siblings to have cooties. I.e. boys will feel that most girls have cooties, but not their sisters.

The psychologist offered this as an explanation: We evolved to find the people we grow up with to be not sexually attractive. This is a mechanism to avoid incest (which can result in genetic problems). However, if you live in a society, you don't want to find people who grow up with you, but who do not share genes with you, to be sexually unattractive (or else you might find no one within your whole society attractive), and thus this "cooties" sensation was placed by evolution so that we can avoid people of the opposite sex during this critical period so that later on, as adults, we may be sexually attracted to them.

It's evolution's way of saying "Not yet".

Why would evolution want to say this? What harm is there in sexual relations before puberty, when pregnancy can't result?

I personally know one girl whom, when she was 8, actively went into sex chat rooms and flirted with older men (anywhere from 16 to 40). I don't think she actually had physical sexual experiences with anyone, though.

I personally know two girls who have had sexual intercourse with adults, one when she was aged 5, the other 8. It was rape in the sense that they were explicitly nonconsentual (they explicitly said didn't want to do it), but it didn't traumatized them. One theory might be that "doing stuff you don't want to do, but adults tell you to do, so you do them anyway" is pretty common at that age (e.g. being forced to clean your room).

I suspect the sex act itself isn't "pleasurable" for them, but having "sexual relationships" with adults may be pleasurable (since the first-mentioned 8 year old sought it out). It may be seen by many of them as a neutral act (like the 5 and second-mentioned 8 year old) and a form of curious exploration.

This is assuming, for lack of a better term, "gentle loving pedophilia". The way pedophilia is often portrayed by mainstream media is violent rape, with screaming, kicking and blood. While I don't personally know of any girl who actually experienced "violent rape pedophilia", I think it's safe to assume that they don't find this pleasurable at all.

Personally, there's a certain fetish that I have, and I remember it causing me erections even before puberty. However, as far as I can recall, the experience didn't feel like anything that I'd call sexual these days. It was something that was pleasant to think about, and it caused physical reactions, but the actual sexual tension wasn't there.

I also recall a friend mentioning a pre-pubescent boy who'd had a habit of masturbating when there was snow outside, because he thought the snow was beautiful. (I'm not sure if she'd known the boy herself or if she'd heard it from someone else, so this may be an unreliable fifth-hand account.) If it was true, then it sounds (like my experience) that part of the hardware was in place, but not the parts that would make it sexual in the adult sense of the word.

Googling for "child sexuality" gives me a report from Linköping University which states on page 17:

The staff caring for 251 children aged two to six of both sexes observed the children’s behaviour and then answered a questionnaire on the behaviours they had observed. ... A total of 6% of the children had at some time been seen to masturbate and this usually occurred during rests. Masturbation took place “often/daily” in only 2% of the children. In almost every case the staff judged the masturbation to be associated with desire and relaxation on the part of the child and not in any case as painful, while one child was considered to masturbate compulsively.

It does, however, also remark that child sexual abuse often causes sexualized behavior in children, and that very little is known about what is actually normal child sexuality. Interestingly, as it relates to the original topic, it also mentions a study that found one third of abuse victims to show no symptoms at all.

Maybe no interest in anything in particular, but what of the sexual gratification itself ? Children do masturbate, it's a known fact. Though maybe it's not universal. But the brain-specific hardware seems to be in place already at any rate.

http://www.med.umich.edu/1libr/pa/pa_bmasturb_hhg.htm

Also anecdotal: I have liked girls continuously since the age of 4. I do not recommend this....

Anecdotal also, I clearly remember watching the same movie (Star Wars) before and after teenage - the sexual tension passed me by completely as a child but was obvious a few years later.

However, I don't have evidence that I'd not have enjoyed sex. The desire instinct was offline, that's all I could swear to.

Anecdotal: I don't remember having the slightest concept of sexual interest in anything before puberty.

This is also my experience.

Hmm, good point - I don't actually know anything about the topic. Sounds like actual orgasm is impossible without puberty (although note it's possible way before adulthood.) Still, pleasure is pleasure. Kids wouldn't enjoy it as much as adults, but some of the adaptations are clearly present - enough for sex to be pleasurable, if not as pleasurable.

Mind you, I personally wouldn't want to change that particular norm without a great deal of thought and investigation by actual experts. But this particular claim seems to be flawed.