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

Attraction is often a tricky concept to corner. Some people look to the stars. Some people play mind games. Some people just snap together like Legos. As the process of courtship goes, our emotions for each other grow and our economical evaluations about one another blur into feelings until one day we find ourselves with a home in the suburbs and a little crying baby in our lap. At many points along that line, we reminisce about all the things that drew us together in the first place: the racing heart when he introduced himself, her exhilarating scent, the wild stay-up-all-night sex, the realization that nobody could ever replace the other. We call it magic, but nature can be seen hard at work at every stage, doing its best to make sure we end up with the right person so that we can raise a smart, healthy family. And you were about to claim all the credit yourself...

Ladies and gentlemen, I give you 10 things you did not know about sexual attraction:

1. Being in love with someone reduces the appeal of other potential partners¹. Nature uses love as a tool to ensure that relationships last beyond courtship and mating, into and past the child-rearing phase. To test this out, a study was done to measure the pull that committed individuals felt toward other people of various levels of attraction. Subjects in two test groups were first primed to think about either extreme happiness or about their love for their partners. Next, both groups were subjected to rapid-fire bursts of images depicting very attractive people and normal-looking people. The researchers measured the reactions of both groups and concluded that the group primed to think about happiness paid the same amount of attention to the attractive and normal-looking photos, while the group that was primed to think about their love paid substantially less attention to the attractive photos. The reminder of their feelings for someone made them oblivious to the attraction of other romances. Knowing this, let's not jump to the conclusion that love is all we need. There are many other factors that go into attraction...

2. Your immune system determines how much you are attracted to someone else². Here comes the science. It all begins with your personal scent; your aromatic essence. Your immune system creates proteins that your body uses and then secretes through your sweat glands. Bacteria on the surface of your skin then break down the proteins and this turns into your own signature perfume. On the receiving end, we find the aroma of compatible immune systems pleasing. If the other person's immune system is diverse enough to yours, your children will grow up with the benefit of a wider variety of resistances. (If you're wondering how that works genetically, it is because the immune system genes can be co-expressed.) There is no ideal scent because we all have a different immune system and this does a bit to level the playing field for everyone who isn't Brad Pitt or Angelina Jolie.

To explain this point further, it should be noted that similar immune systems discourage each other from bonding. As we know, siblings mating together can result in the passage of recessive genetic defects and weakened immune systems. Even in non-related couples with similar immune systems, the occurrence of cheating increases with the percent of human leukocyte antigen (HLA) genes that the two people share³.

3. Gay men enjoy the scent of other gay men, but not of straight men. Talk about gay-dar. This was tested in a blind study where natural scents were collected from 4 groups of subjects: heterosexual men, homosexual men, heterosexual women, and homosexual women. Each individual scent sample was combined with the others of their group to create a generic example scent representing the sexual orientation. The second stage of the experiment had other members of those 4 groups actually smelling the combined samples. The results of their sniffing: "Heterosexual men, heterosexual females, and lesbians preferred odors from heterosexual males over odors from gay males; gay males preferred odors from other gay males⁴." Another interesting result was that gay males preferred odors from straight women over straight men. This provides some solid evidence of homosexuality being a natural occurrence, but unfortunately the people who refute that don't listen to science in the first place.

4. Babies can evaluate attractiveness, even at under a week old⁵. Beauty is not always in the eye of the beholder. Nature has a fairly simple standard of eligibility: symmetry. Even birds with more symmetrical tail features get more action than those with physical quirks. These values are not learned, either; they are evident within us as soon as we're born. In an experiment, researchers first had adults rate pictures of people based on their attractiveness, then they presented these pictures to newborn infants. The babies spent much more time looking at the attractive pictures than the less appealing ones. This still does not explain why Oscar the Grouch is so popular.

5. Women have more orgasms with men who have symmetrical bodies⁶. As with babies liking more symmetrical (thus more attractive) faces, it should be noted that attractive men are more suitable mates. As uneasy as that sounds, a simple survey was done that found 60% of women had orgasms with their partners, but among the respondents whose partners were more symmetrical, the rate was 75%. Those with more asymmetrical partners? 30%. We're not saying that symmetry is the only factor here, but it is an indicator of the many other qualities that go into evolutionary eligibility. For starters, an attractive male is more likely to be confident and more dominant, and that plays into lovemaking considerably. To compound matters further, orgasms help women feel more attached to their partners. Bachelors: you're playing with fire when you tease the orgasm god.

6. Looking an attractive person in the eye makes the brain anticipate a reward⁷. We've all felt that thrill when our eyes meet those of a really hot woman or man. We know it is a bit of anxiety, but what kind exactly? I would say it is a lot closer to watching your bowling ball roll down the lane than, say, the first day of school. The ventral striatum is an area of the brain that starts to spark when a reward is expected. This is the area that scientists notice gets a lot of play when people look at others who are attractive to them. The potential for social interaction gives the brain a little push forward. This is when you introduce yourself and start a conversation.

7. Humans are more likely to choose between two similar partners instead of considering a third, unique choice⁸. This is a very profound concept when you see it in action. In an experiment, pictures of two different-looking yet attractive people (Tom and Jerry) were displayed along with a third picture. This third picture was variable; half of the time, the third picture was a slightly modified version of Tom, only uglier (Tom's evil twin). The other half of the time, it was an "uglified" version of Jerry (Jerry's evil twin). When asked to choose between the three pictures, survey subjects more frequently chose Tom when his evil twin was present and they chose Jerry when his evil twin was around. The lesson here is that we need a standard of comparison to decide if something is good or not. We're able to determine that Tom is a better choice than his evil twin, but we don't know how Jerry stacks up because he is the orange to Tom's apple. It is suggested that in order to ensure success at the bar, you should take a slightly uglier version of yourself as your wingman.

8. Kissing may have evolved from "pre-chewing" by mothers for their infants⁹. Kisses are very special to us and are a huge part of the courtship process. A lot of information is exchanged with a kiss: smell, taste, body language. In fact, 59% of men and 66% of women reported having been attracted to someone, but losing interest after a sub-par first kiss¹⁰. But how did kissing become so important in the first place? One theory is that the intimacy of a kiss could have evolved from the act of a mother masticating food and passing it off for their baby to eat. If this idea suddenly makes kissing a little less attractive, you can think of it as a symbolic gesture of nurturing and care. There, all better.

9. Women are just as quick to be aroused as men, they just are not as aware¹¹. We've all been told that we need to pre-heat the oven before we can start cooking. The truth, however, is that women heat up just as fast as men. Not only that, women become aroused by a wider variety of sexual imagery than men, including pictures of animals mating. Thermal images show that blood rushes to their genitals, but they are not always quite conscious of this until they are closer to their peak arousal¹². When timed in comparison with men, it was found that both sexes reached peak arousal within 10 minutes. To add even more stereotype-busting quality to this point, it was found that when looking at porn, men spend more time looking at faces, while women let their eyes wander to genital areas just as much as men do¹³.

10. Monkeys will pay for porn, too¹⁴. Do you think there could possibly be a market for this? When offered the chance to view pictures of female monkey bottoms in exchange for their fruit juice, male rhesus monkeys emphatically paid up. There was no comment in the study if the monkeys got excited enough to spill their rhesus pieces all over their cage or not.

Thank you for reading. Stay tuned for the SEX Edition! As usual, I will leave you with some bonus facts:

- Twins can come from 2 different fathers.

- Sexual scents activate the pleasure center of the brain rather than the olfactory center.

- Darker males tend to have healthier sperm as a function of the amount of folate in their body.

- Plastic surgery has existed for centuries.

- Women smell better to men when they are fertile

- The more attractive the man, the more short-term sexual partners he has.

- Women work to be more attractive while they're fertile, even when married.

- "Spring fever" is caused by the body slowing melatonin production when the sun comes out after a cold, dark winter. Melatonin aids sleep, but also suppresses moods.

Sources:
1. G. C. Gonzaga, M. G. Haselton, J. Smurda, M. S. Davies, and J. C. Poore, "Love, Desire and the Suppression of Thoughts of Romantic Alternatives," Evolution and Human Behavior 29 (2008): 119-126.
2. C. Wedekind, T. Seebeck, F. Bettens, and A. J. Paepke, "MHC-Dependent Mate Preferences in Humans," Proc Biol Sci 260, no. 1359 (1995): 245-249.
3. C. E. Garver-Apgar, S. W. Gangestad, R. Thornhill, R. D. Miller, and J. J. Olp, "Major Histocompatibility Complex Alleles, Sexual Responsivity, and Unfaithfulness in Romantic Couples," Psych Sci 17 (2006): 830-835.
4. Y. Martins, G. Preti, C. R. Crabtree, T. Runyan, A. A. Vainius, and C. J. Wysocki, "Preference for Human Body Odors Is Influenced by Gender and Sexual Orientation," Psychological Science 16 (2005): 694-701.
5. A. Slater quoted by A. Gosline, "Babies Prefer to Gaze upon Beautiful Faces," New Scientist, September 6, 2004.
6. R. Thornhill, S. W. Gangestad, and R. Comer, "Human Female Orgasm and Mate Fluctuating Asymmetry," Animal Behavior 50, no. 6 (1995): 1601-1615.
7. K. K. Kampe, C. D. Frith, R. J. Dolan, and U. Frith, "Reward Value of Attractiveness and Gaze," Nature 413,no. 6856 (2001): 589.
8. C. Sedikides, D. Ariely, and N. Olsen, "Contextual and Procedural Determinants of Partner Selection: On Asymmetric Dominance and Prominance," Social Cognition (1999).
9. D. Morris, The Human Zoo (1969).
10. S. M. Hughes, M. A. Harrison, and G. G. Gallup Jr., "Sex Differences in Romantic Kissing Among College Students: An Evolutionary Perspective," Evolutionary Psychology 5, no. 3 (2007): 612-631.
11. M.L. Chivers, G. Rieger, E. Latty, and J. M. Bailey, "A Sex Difference in the Specificity of Sexual Arousal," Psychol Sci 15, no. 11 (2004): 736-744.
12. T. M. Kukkonen, Y. M. Binik, R. Amsel, and S. Carrier, "Thermography as a Physiological Measure of Sexual Arousal in Both Men and Women," Journal of Sexual Medicine 4 (2007): 93-105.
13. H. A. Rupp and K. Wallen, "Sex Difference in Viewing Sexual Stimuli: An Eye-Tracking Study in Men and Women," Hormones and Behavior 51, no. 4 (2007): 524-533.
14. R. O. Deaner, A. V. Khera, and M. L. Platt, "Monkeys Pay Per View: Adaptive Valuation of Social Images by Rhesus Macaques," Curr Biol 15, no. 6 (2005): 543-548.