10 Things You Didn't Know About Sexual Biology (Female Edition)

I've collected these little bits of information in my research into sexuality and I thought they'd be interesting to know. This is the female edition, with details normally pertaining to those of the fairer sex.

1. The average age of puberty in females has dropped from 17 to 12 over the last 150 years and there are 3 correlated theories as to why. First, the increase in daily stress that modern society forces children to be aware of is linked to the onset of puberty (known as the psychosocial acceleration theory). Second, the increase in frequency of girls who grow up around unrelated men (not their biological father or brother) influences the trend further (American Journal of Human Biology, 2006). Third, the problem of childhood obesity is a clear factor in the onset of puberty, with the amount of fat on a child's hips signaling the reproductive system to kick into gear.

2. Humans are the only mammals whose breasts are prominent when they are not nursing. All other mammals' breasts expand when they are nursing and contract when their young grow past that stage. The reason for this could be that we need that extra fat for emergency nutrition OR...

3. Human breasts may have developed to mimic buttocks. We know that the preferred mating style of most mammals is from behind, where the shape and color of animal buttocks is a beacon of fertility, but as humans grew to walk upright, our mating style changed too. Thus, the female breasts mimic the shape of buttocks (a theory by Desmond Morris) as we perform coitus face to face. It's no wonder we find both equally arousing.

4. A mother's breast milk changes in composition to suit her infant's age. The age-specific "formula" of breast milk helps the infant develop with the right nutrients needed at its stage of development. This is actually something that Swedish doctors know already, as breast milk banks in Sweden collect, categorize and distribute their milk by infant age. This makes you wish other countries would catch on to this trend like they did with Ikea.

5. There is a 5% chance for a human to be born with a 3rd nipple. They usually develop along the "milk line" which runs from the armpit, through the chest and down to the inner thigh, but they can occasionally pop up anywhere. Lily Allen has one. So does Mark Wahlberg. In the case an owner develops breast cancer, it is most likely to occur around the 3rd nipple. (New England Journal of Medicine, 2005)

6. Women with a large size differential between breasts are more likely to develop breast cancer. "Asymmetrical breasts could prove to be reliable indicators of future breast disease in women and this factor should be considered in a woman's risk profile." (Breast Cancer Research, 2006) We humans are attracted to symmetry and health, so it is convenient that an off-balance pair of breasts might turn a man off.

7. Women with wide hips and thin waists are, in fact, more fertile. Their bodies contain 30% more of the hormone estradiol than average (Ellison & Lipson, 2004). Estradiol plays a huge part in the sexual development and functioning of a woman and 30% more means that a woman is about 3 times more likely to get pregnant.

8. Curvy mothers have smarter kids. With data from the National Center for Health Statistics, two scientists discerned that women with a waist-to-hip ratio of 7 or 8-to-10 tend to have kids who score higher on intelligence tests. This is most likely due to the prevalence of fatty acids that help develop a fetus' brain. (Lassek & Gaulin, 2007)

9. The occurrence of pubic lice ("crabs") has reduced since the Brazilian wax became popularized. It makes a lot of sense, too. Just like deforestation kills animals that live in the woods... That isn't to say we should all get "ripped" immediately. Pubic hair is very important for the emanation of your personal scent because it fosters the organisms that break down your sweat into an aroma. Pubic hair is also a natural signal for fertility. You know what they say: if there's grass on the field, play ball.

10. In the 18th century, there was another term for vagina: "hey nonny-no." Can't wait to hear that one on the street.

Here are a few bonus facts:

- Most girls do not actually ovulate until a year or two after their first period. Right now the common misconception is that once you start your periods, you're fertile.

- The protein responsible for signaling puberty in girls is called "kisspeptin," named after Hershey Kisses.

- The average breast size has increased from 34B to 36C over the last 10 years.

- Males can lactate under extreme starvation.

- Newborns can also lactate because their bodies are flooded with hormones passed on to them from their mother.

- Tampons were a hard sell in the 1920's until marketers developed a way for women to pay for them without talking to a clerk. Thus, it became one of the first self-service products in American retail history. (Heinrich & Batchelor, 2004)

Thanks for reading and I hope you learned something. Stay tuned for the Male Edition.