The chemistry of love

Men have always suspected it, but now there’s scientific evidence: chocolate makes females more interested in sex.

OK, so maybe that’s oversimplifying. What the study announced just before Valentine’s Day (appropriately enough) really said was that a “messenger protein” called DARPP-32 makes female rodents more interested in sex. But even the study’s lead author, Dr. Shaila Mani, a molecular biologist with Baylor College of Medicine in Houston, Texas, made the connection.

Dr. Mani said that sensory cues such as soft lights, wine and, yes, chocolate, stimulate the brain’s production of dopamine. Dopamine, in turn, activates DARPP-32, which gears up the interest in sex.

Dr. Mani studied female mice and rats, who don’t have sex just for pleasure. They’re only interested in it six to 10 hours every four days, when they are at their most fertile. When those few hours roll around, they become flirtatious: they try to attract a male’s attention by biting him and chewing on his ears, then turn around and raise their tails and arch their backs.

Dr. Mani used a set of female rodents genetically altered so their brains produced no DARPP-32, and another set in which DARPP-32 was inactivated by drugs. Both sets had their ovaries removed to stop their natural production of sex hormones. When they were injected with female sex hormones, progesterone and estrogen, it had no affect, indicating that sex hormones must be activated by DARPP-32 to do their work.

It’s just one more indication that love, in the biological sense, is based on chemicals. That “spark” you feel when you touch the hand of someone special is the start of a flood of chemicals that cause you to flush, to breathe harder, to sweat–the same effect that suddenly coming face to face with a bear would have, actually, but context is everything.

The euphoria of falling in love is a kissing cousin (so to speak) of the euphoria you feel when you’re doped to the gills for a root canal. Many of the chemicals our bodies release when we come in contact with someone we find attractive are similar to amphetamines. One of them, phenylethylamine, or PEA for short, literally makes you high and causes you to do silly things like break into song in a crowded elevator.

Like any other drug, however, you need more and more PEA to get the same kick: your body builds up resistance. That’s why the initial euphoria fades over two or three years (or faster, in some cases). (Chocolate, by the way, is also high in PEA, but apparently it doesn’t do anything to boost the body’s supply.)

Some people are literally addicted to that euphoria and so seek out relationship after relationship, trying to recapture it. For those who stick it out, however, a new set of chemicals comes into play. The continued presence of one particular person causes your brain to gradually step up the production of endorphins, which are soothing: they’re natural pain-killers. Thus, your long-term relationship brings you a feeling of security, peace and calm. But when that relationship ends, through death or permanent separation, you feel awful–like a wounded soldier addicted to morphine, you’re no longer getting your daily hit of narcotic.

Recent research that found evidence of romantic love in at least 147 of 166 cultures that were studied. Most scientists are now willing to concede that the capacity and desire to love is hardwired into our genetic makeup.

Why? Well, the evolutionary explanation is that about four million years ago our ancestors started standing upright–and suddenly started seeing each other in an entirely different way. An upright animal displays a lot more of its physical and sexual characteristics than does a four-footed one, which makes the process of choosing a mate much more interesting, opening the door to romance. The pair-bonding that romance engenders, in turn, had an evolutionary benefit in that it increased the likelihood the offspring of the mating would survive.

However, the tendency toward “playing around” may also be part of our genetic makeup, say biologists. A male who mated with more than one female had a better chance of passing on his genes–and a female who mated with more than one male, if she could do so secretly, could have two males supporting her and her offspring.

Yet, amazingly, in light of Dr. Mani’s new research, our distant ancestors managed all of this soap-opera-ish activity without chocolate.

I wonder what they knew that we don’t?

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