Imagine a person who is both male and female and not just on the inside. Literally imagine, half of this person is visibly male and the other half is female. It happens. A rare half-male, half-female butterfly has been discovered. A condition called bilateral gynandromorphy means the butterfly is split down the middle: half male, half female. The wing on the left is typical of a male Lexias pardalis butterfly. The wing on the right is typical of a female. In addition, the butterfly's body is also half male and half female. The butterfly, which is no longer alive, was a resident of the Academy of Natural Sciences of Drexel University. Museum staff noticed the interesting features as soon as it emerged from its cocoon and spread its wings. According to researchers, "Gynandromorphism is most frequently noticed in bird and butterfly species where the two sexes have very different coloration. It can result from non-disjunction of sex chromosomes, an error that sometimes occurs during the division of chromosomes at a very early stage of development." This condition is different from hermaphroditism, where the outward characteristics of only one gender would be present. The condition is quite rare. It is also difficult to spot in species where both sexes look alike. Several theories exist that explain how this rare oddity occurs in animals such as birds. One theory is that bilateral gynandromorphs are chimeras, two separate embryos that fuse together in early development. They are essentially the opposite of identical twins where one embryo separates into two. Another hypothesis is that gynandromorphism in birds happens when the sex chromosomes are unable to separate in the first cell division after fertilization. Still others suggest that the error occurs in the formation of the egg itself. The egg accidentally ends up carrying two chromosomes, one of each sex, rather than the single chromosome it should possess.