This midline -- think of the dorsal, tail and anal fins of a fish - is where the genetic template to produce fins originated, about 100 million years before paired fins evolved and about 200 million years before paired fins evolved into limbs, according to University of Florida genetics researchers. The findings, published online today in the journal Nature, also provide insight into the evolutionary history of genes involved in human birth defects.

"Given that paired fins made their evolutionary debut at a particular location on the sides of the body, intuitively one would think the genetic tools for fin development would be brought together in that place," said developmental biologist Martin Cohn, Ph.D., an associate professor with the UF departments of zoology and anatomy and cell biology and a member of the UF Genetics Institute. "We've discovered that the genetic circuitry for building limbs first appeared in an entirely different place - the midline of the animal."