The biology of attraction

The biology of attraction

Suzanne and Tony met on a blind date. After dating for six months, they were married. Now together for 9 years, they both joke that “It was love at first sight.”

Have you ever wondered how and why you picked your mate? Some people will say it was their partner’s eyes, or perhaps their particular sense of humor or world view. Others say the attraction was a feeling of familiarity or a certain comfort level that created an instant bond. What might be engaging to some people is not to others, and the rationale of our attraction often remains a mystery even to ourselves.

Experts in many disciplines have pondered the subject of attraction and theorized why we make the selections we do. Psychologists believe that locating a mate is dependent on each individual’s particular desires. Freud claimed that mate selection was a reflection of your relationship with your parent, and the psychologist Winch saw mate selection as a way of satisfying complementary needs. Anthropologists, on the other hand, see mate selection as part of a complex cultural system with many tacit rules that often remain unarticulated, but which we follow nevertheless.

For biologists, however, theories of sexual selection usually involve survival and the understanding that mate selection is based on a conscious or unconscious desire to thrive and procreate. Following this line of reasoning, females are generally attracted to large males, as they would be most likely to provide for and protect a family. But there also may be other more subtle biological factors at work.

Using your nose

Scientists have always been interested in the way animals react to smell. They’ve learned that certain smells are defensive, while others are used to attract the opposite sex. Humans too, may rely on their olfactory senses to determine a suitable mate. Experiments by Claus Wedekind at the University of Bern indicate that women can distinguish between men who smell like family–brothers or fathers–and men that smell like mates or lovers, and will choose accordingly.

Using sweaty and smelly T-shirts rather than real men, Wedekind asked women to assign a rating as to whether they smelled unpleasant or “sexy.” The ones they liked best belonged to men who had immune systems different than their own, a choice that would make a child born of that coupling a healthy one. Children born of parents who have two very different types of immune systems have a combined immune system that can fight off a greater number of diseases.

This research indicates the importance of smell, but it may also point to the existence of pheromones, chemical signals that carry a wide range of biological messages. A recent study in the journal Nature provides some proof of this chemical interaction among humans, a long known fact in the animal kingdom but still under debate when it comes to humans. Using an underarm perspiration sample taken from one group of women during a particular point in their menstrual cycle, psychologist Martha McClintock of the University of Chicago was able to change the length of a second group’s menstrual cycle by exposing them to the sample from the first group.

It is generally thought that pheromones are not “smelled” but are instead, “detected” through what is termed the vomeronasal system (VNO). Although there is still a great deal of discussion as to if and how this works in humans, the VNO system does appear to consist of a small receptor in the nose and a network of nerves throughout the brain, which end up in the hypothalamus–the brain’s center for emotions and basic drives.

Do we always choose the best genes?

While Wedekind’s research indicates that females can, albeit unconsciously, detect who will make a biologically sound sexual partner, other researchers disagree. In fact, a recent article in the journal Science claims that the “good genes” model of mate selection has been too highly emphasized. Drawing on work in animal behavior, sensory biology, phylogenetics and artificial neural network models, Dr. Michael J. Ryan of the University of Texas at Austin has developed a theory showing that animals might make choices that do not directly enhance the mate’s odds of survival.

According to his theory, animals have “pre-existing preferences” or “receiver biases” that evolve in the context of activities other than reproduction, yet can carry over into mate selection once they become established. For example, during the gathering of food, a sensitivity to the color red might be of help to a particular species of bird. In turn, birds with a predilection for red will be more likely to thrive and reproduce, and they will carry with them a pre-existing preference for the color red.

Once established, the color red will become a key part of the courtship ritual. Female birds, already primed to prefer the color, will pick mates with red breasts over those without, and will be more inclined to choose those birds that enhance their appearance by puffing out their red chests. As a consequence, these birds will be more likely to reproduce and will also continue this very specific mating ritual as a way of exploiting the females already established received biases. As Ryan explains it, “any sensory system is going to be more responsive to some stimuli than others. If males have a variety of options by which to signal their sexual interest, females will favor those who use signals they are already keyed into.”

Many pre-existing preferences are part of an evolutionary process, but some appear to be “hard-wired’ in the brain. The human preference for facial symmetry relies on a traditional argument that claims asymmetrical faces indicate a hidden health problem that keeps potential mates away. Ryan, however, suggests a simpler explanation. Human perception may simply respond better to symmetrical cues.

But is it love?

While we certainly like to think that we have some power over the process of mate selection, according to biologists, many choices may be made on an unconscious level. In fact, the way we describe the sensation of attraction as “falling in love” surely indicates that sometimes we have little or no control. “Love” may be even more mysterious than we–or the twelfth century English poets–thought.

Scroll to Top