Summary

While Shubin and his colleagues were digging up the Tiktaalik in the Arctic, Randy Dahn, a researcher in his lab was in Chicago conducting genetic experiments with the embryos of sharks and skates. He injected strong doses of Vitamin A in the eggs containing skate embryos. The goal was to find the DNA code that builds bodies from eggs. This quest would take them from the human hand to shark fins and to the wings of flies. Shubin’s lab is split between work on fossils and embryo DNA.

DNA provides instructions to build diverse cells – limbs, nerves, organs – but they all contain the same DNA. What creates different results are the genes that are turned on in each cell. Genetic switches control the genes in each cell. At conception, a single cell contains all the DNA code necessary to build the body...