Our limbs and other symmetrical body parts develop from separate fetal structures. But what about our eyes? The question is prompted in part by birth defects that produce a cyclopean eye, suggesting that a single structure gives rise to two eyes. Molecular neurobiologist Yi Rao now argues that, indeed, our two eyes begin as one. Rao, who works at Washington University School of Medicine, tracked eye development in embryonic frogs of the genus Xenopus. In particular, he isolated a gene that may control eye development. He found that the two dark spots in the 21-hour-old embryo (second from top), which later form the eyes (third from top), split from an earlier single band (top). When he removed a part of the tadpoles’ brains that signals the shutdown of the gene in cells in the middle of the single eye band, allowing two separate eyes to form, he found that one-eyed tadpoles (bottom) were the frightful result. Although we did most of the studies in frogs, we also followed with chick embryos and found cyclopean eyes, which is important because amphibians and birds are very different, says Rao. This suggests that it is general to all vertebrate species.