Any ideas on why humans have lost estrus and mate all throughout the menstrual cycle? The theory of concealed ovulation doesn't seem likely since there are still signs of fertility like changes in body odour that men could pick up on and know when a women's fertile. It seems more likely that instead of being concealed fertility just isn't actively advertised any more. Maybe we evolved to have sex throughout the menstrual cycle first and then it became unnecessary for women to advertise when their fertile. But then why did we evolve to do that?

One theory is that concealed ovulation promotes pair-bonding (benefitting females), as males are more willing to commit to females whose fertility isn't easy to predict. The other thing is that anthropologists reckon that humans never had to evolve to conceal ovulation because we never really advertised it (our ancestors didn't have big swollen chimp-like bottoms). The signs that men (and women) can pick up on are probably 'leaky cues': not advertisements per se, but detectable because it's in men's best interests to attend to them (not always to women's benefit).

How about investigating how skin colour and texture (and attractiveness) vary with age? Have you noticed how the skin of adolescent girls has an eye-catching sparkle? This is quickly lost as they move into adulthood and then they might try to artificially recreate it with make up.

Take a look at this picture of Jordyn Jones at about 14 with no make up as far as I can tell:

http://flockdraw.casfire.com/ups/156362.jpg

And look at these porn stars with and without make up:

http://flockdraw.casfire.com/ups/156363.jpg

What the porn stars are doing is using makeup to recreate the natural sparkle that young adolescent girls have and get male attention. It's interesting that women's skin changes a bit over the cycle but these changes are nothing compared to those that come with age. It's the elephant in the room, isn't it?

Research on make up (I have an Episode where I interview Alex Jones about it) suggests that make up probably exaggerates the difference between male and female faces. Clearly agae also comes into it, as skin colour is less even as we age and is simulated with foundation use.

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Sorry to be annoying but there's one other thing I'd like to ask you which is why do girls become interested in sex before they're ready to start reproducing?

Societies around the world have different opinions on when a girl should start having sex. Here in England the law says it shouldn't be before age 16. A foraging tribe in the jungle may believe it shouldn't be until after a girl has her first period. But the reality is that girls (and boys, for that matter) usually develop a sex drive at about 12. This seems to be the kind of age that nature intended for girls to start seeking out and attracting sexual partners. What's interesting is that at 12 most girls aren't yet reliably fertile and it's rare for girls to become pregnant at that age if having unprotected sex.

So what could be the function of a girl's pre-fertile sex drive? Attracting potential husbands? Getting male attention and inciting them to compete over her?

I reckon it's probably to do with getting male attention and being chosen as a wife. Women in ancestral societies were usually married off much earlier than today, probably about 12-16, as they were on the verge of reproductive age. This makes biological sense since by acquiring a female just before she reaches reproductive age a man can potentially have all her fertile years to himself and would start getting offspring from her quickly. If this was the typical age girls were acquired as wives we would expect them to have evolved to do what they can to get chosen by the best men.

Growing eye-catching perky boobs at this age is probably one such thing. Have you ever seen what woman's boobs look like in a natural hunter-gatherer society? Effing gross. By the time a woman's in her 20s she's had a baby or two and her boobs have gone saggy from breast feeding. The boobs of a childless 14 year old girl on the other hand are deliciously perky and grab your attention. That's what they're for. They're an honest signal saying "I haven't started reproducing yet but I'm close to doing so, so now's the best time to pick me as a wife. Come and get me, lads!". Watch "Tears of the Amazon" to see what I mean about this.

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Becoming interested in sex and behaving more sexually is probably another way of getting male attention. Imagine some mutation happened that made a girl become interested in sex a few years before reaching actual reproductive age, around the time she was typically chosen as a wife. It's easy to imagine that a girl with this mutation would get more attention from the males and the males would be more likely to compete for her. Mating in prehistory wasn't as peaceful and civilised as it is today. All across the animal kingdom the males fight and often kill each other over the females and there's no reason to think our species was any different. In fact we know it isn't because we see men fighting over girls in primitive hunter-gatherer societies today. Even in the so-called gentle, peaceful Kalahari tribe the men often fight with each other for the right to marry a young girl who's just grown a pair of boobs and is approaching reproductive age. When a girl sprouts boobs and starts behaving more sexually the men notice and want her for themselves. Imagine them thinking and saying: "Oh, she's so lovely, I want her! Back off, I'm having this one. I said back off, she's mine! You wanna fight, do ya?". She gets male attention and the males are incited to compete for her. That's exactly how the system is supposed to work.

This video kind of shows what I'm getting at:

https://www.youtube.com/watch?v=hsuoQ-46NB4

Just look at the amount of male attention these two 12 year old girls are getting. If this scene happened back in caveman times before there were police and governments to make people behave I'm sure the men would start fighting and the winners would take the girls for themselves.

Dancing could be another way for girls to get attention. Take a look at the amount of videos on youtube or younow showing girls about 12-16 dancing. They absolutely love it.

In talking about girls getting male attention I don't necessarily mean they're doing this consciously, rather that they've evolved to behave in ways that do so. Their personal intentions in, say, wearing sparkly makeup may be to make themselves them feel pretty but the effect this has is to get male attention. I trust you're smart enough to understand the proximate/ultimate cause distinction, because a lot of people don't seem to.

You could call it the Lolita phenomenon. In the story Lolita was acting like a slut and having having sex with men at 12, 14 kind of age but she didn't actually get pregnant until she was 17, which was probably the typical kind of age that girls got pregnant for the first time in prehistory too. So what could have been the biological function of her sex drive at 12, 14? Well, it got men chasing after her and competing for her, didn't it?

One thing I should point out is that although pregnancy is often dangerous for girls about 12-14 it doesn't happen very often so the overall risk is small. Girls who get pregnant at, say, 12 suffer higher rates of complications and end up leaving behind fewer descendants than girls who start reproducing at a later age. Over time girls who start reproducing at 12 become a minority in the population and evolution will select in some way to reduce the rate at which 12 year old girls get pregnant. One of the simplest ways of doing this is to select for low fertility which is what appears to have happened. Girls rarely get pregnant at that age, they're simply not very fertile, although there is still some danger. Since girls are very often interested in having sex at 12-14 kind of age (come on, be realistic), the benefits that come with being interested in having sex at that age must outweigh the risk of the occasional disastrous pregnancy. Getting male attention is basically what I believe those benefits are.

LOL BUMFACE, you're a bit of a pervert but you're right. The girls here in Manchester often drop their knickers at 12 but they're not properly fertile or capable of safely having a baby at that age. What's going on?

The earlier a female starts reproducing the more offspring she can have in total but only to a point otherwise they would have evolved to start reproducing in infancy to give themselves the longest reproductive lifespan possible. The problem is that if a female starts reproducing too young the risks of pregnancy and childbirth etc are too high and will cancel out the benefits of the longer reproductive lifespan. The optimal age to start reproducing would be a compromise between these two factors.

In modern foraging societies that are living something like prehistoric people the typical age girls get pregnant for the first time is about 16. This must be the optimal age. Girls who start later than 16 leave behind fewer descendants due to their shorter reproductive lifespan and girls who start earlier also leave behind fewer because they have higher risks of dying in childbirth etc. Girls who start about 16 have the greatest number of surviving offspring and have come to dominate in these populations so 16 has become the typical age of first pregnancy. If girls who started at say 12 were the most reproductively successful then 12 would have become the typical age of first pregnancy but it's not.

So if 16 is the optimal age for girls to start reproducing why are they interested in sex before then? Why run the risk of getting pregnant early and leaving behind a sub-optimal number of descendants, possibly none if she dies in childbirth at 12 or 14? It could be that the interest in sex girls have before 16 is a by-product of some other adaptation that evolution can't select out without causing disruption elsewhere but this seems unlikely. Why wouldn't evolution be able to change a simple thing like the age that females become interested in having sex? It must only involve a few thresholds and developmental timings that could be easily altered. Instead it seems to be an actual adaptation. The benefits of being interested in sex at that age must outweigh the risks of occasional early pregnancy but what are those benefits? Something social? Getting male attention?