Poets have swooned over it since the invention of the written word; singers started crooning about it even before that time. It is a central theme in our daily lives, from the books we read to the people who make our hearts beat a little faster. It's what "makes the world go 'round."
Love as we know it, however, remains an intangible
feeling. No definitive method exists to calculate or predict
to whom we will be attracted. For the most part, attraction
remains an unsolved mystery--until now.
From the same discipline that brought the mysteries of genetic inheritance into the realm of understanding, science has begun to tackle a new question: what causes attraction. Recent experiments involving everything from sweaty T-shirts to facial symmetry have started to piece together some of the clues to this enormously complex phenomenon. Not surprisingly, the unifying theme behind all of this new information is one common to biology: evolutionary fitness.
"Judging beauty has a strong evolutionary component. You're looking at another person and figuring out whether you want your children to carry that person's genes," says Devendra Singh, a professor of psychology at the University of Texas.1 The scientific properties of attraction (to whatever extent they are involved) can be explained by the simple will to produce viable offspring, also know as healthy kids.
Beyond this underlying principle of attraction, one begins to wonder how, and on what level, one can judge the fitness of another person. Certainly, a person smitten for the first time at a bar doesn't ask for a genetic sequence and specifics about that special someone's immune system before approaching him or her.
Yet some of that information is received and interpreted at a sub-conscious level, yielding all of the necessary information to trigger attraction without any expensive tests. The study of attraction has so far identified two main ways in which fitness information can be encoded from one person to another: pheromones and body form.
Scientists have known for quite some time that pheromones (chemically-secreted, odorless, airborne molecules) can trigger large sexual responses in non-human animals, but up until recently they had assumed that humans had lost the ability to use this "sixth sense."
In 1985, researchers at the University of Colorado found vomeronasal organs (VNOs, organs that receives pheromone molecules) in human nostrils.2 Coincidentally, VNOs connect directly to a part of the brain responsible for basic drives and emotions.
Shortly thereafter, the VNO was correlated to brain activity, causing a sudden surge in pheromone research. Now, "pheromone" has become a biological buzzword for the nineties.
One of the first and most famous experiments on the science of attraction asked women to rate intensity, pleasantness, and sexiness based on men's sweaty T-shirts. Claus Wedekind of the Zoological Institute at Bern University in Switzerland wanted to see if women could differentiate between men with similar and dissimilar immune systems.
Dr. Wedekind believed that women, using pheromones as signals, would rate T-shirts from men with dissimilar immune systems higher on all three counts, thus making the likelihood of genetically diverse, healthy offspring greater. He found that "women... who are dissimilar to a particular male's MHC [immune system markers of identity] perceive his odor as more pleasant than women whose MHC is more similar to that of the test man (3)."
Further evidence that pheromones might play a role in
attraction was found by Dr. Carole Ober of the University of
Chicago's 
Department
of Human Genetics. Her group took DNA samples from an
isolated religious group called the Hutterites. This group
from South Dakota marries among themselves and tends to have
large families. The Hutterites descend from 64 European
immigrants and thus have a similar genetic make-up,
including immune system types (3).
The University of Chicago group examined the haplotype matches of MHC immune system markers for couples. Random pairings in the colony, based on genetic data generated by a computer simulation, were compared to the colonies' actual couples. The simulation predicted many more haplotype-matched couples (identical immune systems) than were actually found in the Hutterites. Dr. Ober's explanation? She believes that pheromones could have prevented couples with identical immune systems from being attracted to each other (3).
Beyond pheromones, many scientists believe that body form, especially symmetry, conveys a sub-conscious message of fitness and initiates attraction. The theory goes that asymmetrical phenotypic features give clues to underlying genetic problems, thus yielding less viable offspring.
One paper published in 1994 explains that symmetry is used "as a means of ascertaining the stress susceptibility of developmental regulatory mechanisms."4 In other words, organisms that maintain symmetrical features under environmental stresses also maintain healthy, unaffected genomes. Symmetry is simply a way for an organism, including a human, to advertise that genetic fitness.
Numerous studies of symmetry in humans have shown that men especially are more attracted to women with symmetrical features. (One hypothesis suggests that women are not as concerned with symmetry because instead of breeding, they look for a mate that can provide food and protection for their offspring, i.e., money and power for humans (2).
In one recent study conducted by Randy Thornhill of the University of New Mexico in Albuquerque, college males found symmetrical female faces more attractive than asymmetrical faces. In addition, the symmetry-blessed women showed a history of more sexual partners and tended to lose their virginity at an earlier age (2). This same pattern for symmetry preference held true for both facial and non-facial characteristics in two additional studies.(1,5)
Besides symmetry, there are other subtle clues to fitness in the human body. Society has often propelled the "hour-glass figure" as a model for all women to strive for, and with good reason. Even this seemingly obvious attracting trait has a biological basis.
Studies have shown that men are most attracted to women with a waist-to-hip ratio of 0.7. A group of researchers at the University of Texas at Austin decided to compare that number to the average ratio of winners of the Miss America pageant and found that the two numbers were identical (2).
The specific 0.7 ratio suggests a woman's fitness and ability to bear children (younger girls lack the curves while older women tend to develop more fat around their waist). Surprising to some, the attractiveness of women with a waist-to-hip ratio of 0.7 holds true over a range of weights (2).
Not everyone is convinced that pheromones and body form control attraction. One skeptic of the idea of pheromone influence, a biologist at Arizona State University, says, "I think mate choice is probably a lot more complicated, particularly in humans."3
Indeed, one must always take into consideration the role of free will in attraction. In addition, many researchers have suggested that pheromones and body form only get the proverbial foot in the door; from there, the course of the relationship is controlled by many other factors, both conscious and sub-conscious.
But the question remains, why are we so fascinated with the science of attraction? Perhaps some are tantalized by the idea of being able to quantify a previously mysterious subject. The idea of identifying love by free-floating molecules and symmetrical features is a radical, if not a scary, way of understanding one of the greatest human mysteries. Others may simply be looking for a date.
Even though the science of attraction is still much debated, you never know: Falling in Love, a new pheromone perfume that runs about $60 for one tenth of an ounce, might be worth the extra cost to attract that future special someone.1
