In 1819, shortly after Moses and Aaron Wilcox arrived in the tiny town of Millsville, Ohio, the identical twins struck a deal with town officials: rename the town Twinsburg in their honor, and they would donate six acres of land for a public square and throw in $20 toward a new school.
Moses and Aaron were lifelong business partners, they married women who were sisters, had the same number of children, contracted the same fatal disease and died within hours of each other.
Today, Twinsburg is the site of the Twins Days Festival, the world's largest annual gathering of twins, with some 2,900 pairs attending this past August.
Six teams of scientists showed up as well, practitioners of a research tradition that goes back to 1875, when English scientist Sir Francis Galton (Darwin's cousin) studied intelligence in twins. Researchers study identical twins -- who develop from a single egg that splits after fertilization and therefore have the same genes -- to learn how genes influence traits or predispose people to disease. If research finds that identical twins who grew up in the same household (and presumably ate the same foods, went to the same schools and so forth) share a particular trait more strongly than do fraternal twins, who come from two, separately fertilized eggs and whose genes are no more alike than those of any other siblings, it suggests the similarity is due to genes rather than environment.
Twin studies have shown that shyness, willingness to take risks and propensity toward holding religious beliefs are genetically inherited to some degree, as is the risk of diseases such as osteoporosis, asthma and heart disease.
Twin studies have even corrected cruel misconceptions: until a 1995 study confirmed that autism was largely genetic, "a generation of women were taught that they caused the autistic behavior in their children by their distant, aloof parenting," Robert Morell, a geneticist at the National Institutes of Health in Bethesda, Md., told Smithsonian magazine for the November issue.
For three years in a row, Morell and co-workers who study hearing have journeyed to Twinsburg. At the most recent conclave, they set up shop under a circus-like tent next to five other research teams.
One day, twins lined up outside the tent to have their fingerprints taken, their health questioned, their sense of smell and taste examined, and the insides of their cheeks swabbed for DNA.
"There are now nearly 100 genes that are known to cause a malfunction in the ability to perceive sound," Morell said at the festival. The genetic contribution to auditory processing is not well understood -- and that's where the twins come in. Each participating twin puts on headphones and takes what is called a dichotic listening test. For about 45 minutes, simple words, like "house" and "spent," are transmitted simultaneously, one in each ear. The twins report which words they hear. If there is a genetic component to auditory processing, identicals should score more similarly than fraternal twins do.
Morell's work is just beginning, but he hopes that identifying auditory processing genes will ultimately help prevent or treat hearing or learning problems in twins and non-twins alike.
Also in the tent that day were representatives of the International Association for Identification, a nonprofit group whose members engage in forensic activities. The group was collecting fingerprints and palm prints to confirm that even those of identical twins differ.
Other researchers were studying skin diseases, incontinence after giving birth and hair loss. Twins' noses wrinkled at the smell-and-taste study table, where scientists were testing genetic predilections for detecting certain herbal compounds or the bitter quinine in tonic water.
One motivation for participating in the tests was money: some experiments paid $10 to $15. Other twins were simply curious about their twindom. In the end, most said they were simply happy to help scientists better understand, or possibly cure, a disease.
"I feel so privileged to have been born a twin, the least I can do is help out in this small way," says Stefanie Nybom from Ontario.