Breast Feeding & Social Chemosignals

A fascinating study conducted by the University of Chicago and the Monell Chemical Senses Center has found that women’s sex drives surge when they are exposed to the chemosignals of other women who are breastfeeding, likely because it signals to them on an unconscious level that environmental and other circumstances are optimal for having a baby.
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The Trouble With Truffles

Truffles are harvested in France and Italy with the aid of either female pigs or truffle dogs, both of which are able to detect the strong smell of mature truffles underneath the surface of the ground, with dogs being preferred by most commercial truffle hunters because they don’t tend to eat the truffles they unearth. But if you’re just looking for a quick snack and not a career, you might want to go with the pig.

Where “truffle dogs” require lengthy training, pigs sniff out the fungal delicacy naturally–and enthusiastically–due to truffles’ production of a substance called androstenone. As luck would have it, androstenone is the potent pheromone found in the saliva of a male pig which will cause a female to immediately assume a mating stance. The cunning trick of nature is a fortunate phenomenon for worldwide lovers of the tasty delicacy, as humans’ inferior noses are unable to detect the truffles before they have passed their peak. It’s presumably less than satisfying for the pig, who does all the work but gets neither the sex nor the truffle.

Love May Be Blind, but It Sure Can Smell

The introduction of birth control pills in the early 1960s has been widely accepted as the chief culprit for the sharply rising divorce rates which followed (from 9.6 per 1000 marriages in 1963 to 19.4 per 1000 marriages ten years later), as fewer women were forced to “think of the children” and remain locked in unhappy marriages. As it turns out, we may have been barking in the right forest but up the wrong tree. While the pill certainly freed women from having to live with unwise choices in long-term mates, it may also be responsible for their having made those unwise choices in the first place.
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Why Jerry Loves Tom

Just as the 98-lb weakling who emerges victorious from a scuffle with a bully might have a better shot at getting lucky, a mouse who has tangled with a predator and lived to boast about it appears much more macho–therefore more appealing–to potential mates. According to recent finding by zoologist Zhang Jianxu and his research group, a male mouse is more attractive to female mice if his scent features even the faintest whiff of his archenemy — the common house cat.

Zhang, working with Sun Lixing from Central Washington University and Kevin Bruce and Milos Novotny, both from Indiana University, exposed 48 mice to regular doses of cat urine over a period of two months. Not only did these mice draw a more favorable reaction from female mice than the control groups (which had been exposed to rabbit urine and water), analysis of their own urine showed distinctly elevated levels of alpha and beta farnesenes–the exact chemicals that send female mice swooning.

Don’t Ask, Don’t Smell

Researchers at the Karolinska Institute in Sweden showed in 2001 that pheromones stimulate the human hypothalamus–a part of the brain that governs sexual arousal. In 2005, they added a fascinating new facet by introducing gay men into the study. “Gay men are a great control group for this kind of study,” says Dean Hamer, a geneticist at the National Institutes of Health, “because they’re pretty much the same as straight men except for that one factor.”

As in the earlier tests, the scientists isolated two substances suspected of being human pheromones–an estrogen-like chemical distilled from women’s urine and a testosterone-related chemical derived from male sweat. Using both MRI and PET scans, the researchers found that women registered the female pheromone in the smell-processing part of the brain. But when women sniffed male pheromones, their hypothalamuses lit up as well. In straight men, the results were exactly the opposite.

And the gay men? Sure enough, when exposed to male pheromones, their hypothalamuses lit up just like the women’s. Female hormones did nothing for them.

While Hamer acknowledges that the gay men’s different brain activity could be either a cause of their sexual orientation or an effect of it, he says, “it certainly seems unlikely that somehow being interested in men would cause the brain to rewire itself in such a dramatic way.” This might be tested, he suggests, by studying the responses of people at different ages to monitor any change from early childhood through adulthood.

Similar testing on lesbian women has proven less conclusive. In 2006, researchers led by Ivanka Savic of the Stockholm Brain Institute and Hans Berglund of the Karolinska University Hospital reported that, while lesbians processed neural responses more like heterosexual men than heterosexual women, the similarity between homosexual men and heterosexual women seemed stronger than the similarity between lesbians and heterosexual men.

Sandra Witelson, a neuroscientist at the Michael G. DeGroote School of Medicine at McMaster University in Ontario, Canada, finds these differences fascinating, suggesting that sexual orientation may well have a different basis in women than in men. “It’s not as simple as gay men being more like women, and lesbians being more like men. There are two sexes, which we know are biologically different in some respects, and variation in sexual behavior within each sex is not necessarily the same as in the other sex.”

Babies Smell (see Olfactory Fact #132)…Even Before They’re Babies!

The Scent of a Woman may have played a more integral role in your conception than just your father’s appreciation of your mother’s Chanel No. 5, according to a 2006 Indiana University Bloomington study. Noting that sperm have olfactory receptor proteins similar to receptors in the nose which attract them to “the site of the action,” the research team constructed a device which fed mouse sperm into a chamber through one tube, ovarian chemicals through a second, and a control buffer solution through a third.
The results?
The snooty sperm tended to turn up their noses at the placebo and navigate right toward the real thing!