Double rows of eyelashes are usually the result of a mutation at FOXC2, a gene that influences all kinds of tissue development in embryos. FOXC2 mutations are thought to be responsible for, among other things, lymphedema-distichiasis syndrome, a hereditary disease that can cause disorders of the lymphatic system in addition to double eyelashes.

The eyelash mutation isn't always as cosmetically enhancing as Taylor's turned out to be--the extra eyelashes can sometimes grow inward and damage the cornea. And it turns out that 7 percent of people with lymphedema-distichiasis syndrome also suffer from congenital heart disease.