The Evolutionary Geometry of Human Anatomy: Discovering Our Inner Fly

The human body is one still frame in a very long evolutionary movie. Anthropologists focus on the last few scenes, whereas geneticists try to trace the screenplay back as far as possible. Despite their divergent time scales (millions versus billions of years), both disciplines share a reliance on a third field of study whose scope spans only a matter of days to months, depending on the organism. Embryology is crucial for understanding both the pliability of anatomy and the modularity of gene circuitry. The relevance of human embryology to anthropology is obvious. What is not so obvious is the notion that equally useful clues about human anatomy can be gleaned by studying the development of the fruit fly, an animal as different from us structurally as it is distant from us evolutionarily. The underlying kinship between ourselves and flies has only become apparent recently, thanks to revelations from the nascent field of evolutionary developmental biology, or evo-devo. All bilaterally symmetric animals, it turns out, share a common matrix of body axes, a common lexicon of intercellular signals, and a common arsenal of genetic gadgetry that evolution has tweaked in different ways in different lineages to produce a dazzling spectrum of shapes and patterns. Anthropologists can exploit this deep commonality to search our genome more profitably for the mutations that steered us so far astray from our fellow apes.