On making predictions and seeing the results Greetings, fellow bilaterians! Back in 1996 a real scientist by the name of Gregory Wray took to comparing the genes in various animals with a view to seeking the time way back when they all shared a common ancestor. He used the idea of a "molecular clock", in which one makes the broad assumption (Yes, they know its "only" an assumption)that genetic differences accumulated at a fairly constant rate over time. Looking at various species and their genes, comparing where they were alike and how much they had drifted apart to make their various species, he estimated that the last common ancestor for all these species on earth to make a bilateral plan for their bodies - that is, where the left half was a mirror image (approximately) of the right half - must have existed about 1.2 billion years ago. This report was followed up by other genetic studies, and they came up with a different set of results, about half that much, somewhere between 573 and 656 million years ago. The earliest bilateral fossils known were dated back to a mere 555 million years ago, so this extra millions of years was kind of controversial. I can only imagine the pain such a report and such a conclusion causes in the hearts of those who believe the earth didn't even show up until about 10 or 6 mere thousand years ago. I can just hear them now hooting over the unsound, useless idea of trying to estimate species divergement dates by such sheer speculation. But there are a lot of scientists out there who really believe the earth is that old and that making such an estimate makes sense, and one of them was David Bottjer. He some colleagues decided that if the molecular evidence said they were out there, then he's going to find fossils of them! Now that meant looking for a fossil of an animal that didn't have any bones, because what makes the Cambrian period such a famously productive time for fossils is that is when organisms suddenly found a need to develop protective bony armor for their soft bodies. There have been a few finds from before that time . . . fossilized matted bacteria, sponges, clumps of algae . . things that are on the verge of being a full fledged bilaterian, but not quite there yet . . . and in 1998, our boy David heard about a place where they were hauling in tiny soft bodied stuff like that from around the right time, 40-55 million years before the Cambrian, over in South China. Well, Dr. Bottjer teamed up with some Chinese scientists and they got a whole truckload of the right rocks from the site and took them back to the lab for very careful, careful examination. They sliced up the rocks into sections so thin the light would shine through them and carefully scanned 10,000 different slides made from the rocks. They found the sponges others had reported. They found the cnidarins others had reported, and please, somebody, tell me - WHAT IS A CNIDARIN? anyway, they also found a precious few itty bitty critters that were multi-celled with a definite bilateral body plan. "Itty bitty" in this context means it was about the size of a typical printed period. In the 10,000 slides they found just 10 actual such animals. They named the species "Vernanimalcula", meaning "small spring animal", because it appeared just after the famous long winter of the "Snowball Earth". So as I was reading about this in the August 2005 issue of Scientific American on pages 42 and following, where Dr. Bottjer himself tells us the whole story of this find, I thought to myself, why here we have a perfect example of the predictive power of evolution theory. The molecular clock notion, which whatever you think about it certainly would never work if evolution were not true, made an estimate of the time to look for very early animals with a bilateral body plan, the rocks for that time were examined, and sure enough, there they were, as predicted. Now if you go up to Dr. Bottjer some day and tell him that evolution theory cannot make predictions that are born out by actual scientific investigation, he will laugh in your face, because he's been there and done that. What's more, he might even take the time to point out that his findings help strengthen the case for the accuracy of the molecular clock idea.