[0:01]So what do we learn by looking at 600 million years of animal history? Evolution's tinkering with mamness to make whales. In the same way, it's tinkering with fishiness to make tetrapods. And it's tinkering with animalness to make all the different body plans that we see. All these different creatures are variations of the same theme. restated over and over again. The question was, what was evolution tinkering with? One of the remarkable discoveries of the last 20 years is that evolution's not tinkering with the bodies. It's tinkering with the recipe, the machinery that builds bodies. What is that recipe? What is that machinery? It's the genes. Scientists had long suspected that embryos held clues to how animals evolve.
[1:03]All embryos start out as clusters of nearly identical cells. But soon, an embryo partitions itself into specialized segments, which develop into the final form of the animal. What controlled this process? How did the embryos know what shape to take? One researcher, Dr. Ed Lewis of Caltech, studied this question for 30 years by cross-breeding thousands of flies. Lewis's work led him to a controversial idea. He proposed that a surprisingly simple mechanism was shaping embryos. He wrote that each segment of the fly was being directed to grow by a single gene. A small set of genes, a kind of genetic toolkit, appeared to be laying out the entire body. In 1994, Walter Garing of the University of Basel isolated the gene that triggered the growth of eyes in fruit flies. The gene was called eyeless, because flies without it developed with no eyes. Garing knew of a gene in mice that worked in the same way. He wondered, were the two genes the same? And this question we tested by taking the mouse gene and putting it into fruit flies. to see whether flies can understand the message of the mouse. Garing replaced a fly's gene for eyes with the mouse gene. And to everybody's surprise, the mouse gene works perfectly well and can induce a compound eye in the fruit fly. The fruit fly grew normal fruit fly eyes using a gene from a mouse. Not only did the two creatures use the same mechanism, they used the same gene. So what this means is, in some ways, some sense, evolution is a simpler process than we first thought. You think about all of the diversity of forms out there. We first believed that this would involve all sorts of novel creations, starting from scratch again and again and again. We now understand that no, that, that evolution works with uh packets of information and uses them in new and different ways in new and different combinations. Without necessarily having to invent anything fundamentally new but new combinations. Suddenly, the commonality of form among animals was understood. Animals resembled each other because they all used the same set of genes to build their bodies. A set of genes inherited from a common ancestor that lived long ago. And there's only one inescapable conclusion you can draw from that, which is, if all of these branches have these genes, then you have to go to the base of that, which is the last common ancestor of all animals. And you deduce, it must have had these genes. So the whole radiation of animals, the whole spring of animal diversity has been fed by essentially the same set of genes.
