Gynandromorphism was first discovered by Bridges and Morgan in Drosophilla. It has been observed in numerous animal species, including crustaceans, such as lobsters and crabs, spiders and many species of bird.[1][2][3][4][5][6] A clear example in birds involves the zebra finch. These birds have lateralised brain structures in the face of a common steroid signal, providing strong evidence for a non-hormonal primary sex mechanism regulating brain differentiation.[7]