A very odd creature flitted past friends James Adams and Irving Finkelstein—a swallowtail unlike any they had ever seen. Its left half was yellow; its right, black. It was as though someone had sliced up two different insects and seamlessly sewn them back together. He could see immediately that he had caught a gynandromorph—an animal that was half-male and half-female.
For hundreds of years, naturalists have been documenting gynandromorphs among insects, spiders, lobsters, and birds. More recently, researchers—aided by increasingly sophisticated laboratory tools—have overturned reigning theories of sexual development by studying such hybrids. As has proven true time and again throughout the history of science, the creatures that seem strangest—those that are too odd, too asymmetrical to fit neatly into our presupposed categories—teach us the most about how all living things work. It turns out, for example, that the standard explanation of how a bird becomes male or female is wrong. Scientists came to this realization not by investigating scores of typical birds, but rather by examining a few gynandromorphs. It all started with an odd zebra finch.
Read the full, original story: Half Male, Half Female, Total Animal