Show Evolution of a Complex Trait? Ok.Jun 13th, 2008 | By Jonathan Golob | Category: Evolution, Featured Articles
No one really argues about the validity of natural selection. Only the most hardened of young Earth creationists contest that organisms with more adaptive traits will preferentially survive and reproduce. The Intelligent Design crowd tends to wave this off as a trivial truth. Of course, they say, better traits are selected for. They instead claim you need a designer to provide these traits. How could something as complicated as a metabolic pathway simply arise from chance? Where’s the proof that such beneficial traits can simply arise, with no guiding hand?
Zachary Blount, Christina Borland, and Richard Lensk, from Michigan State University, set out to test this tricky question in evolution.
E. Coli, a gut bacteria commonly used in the lab, cannot eat citrate. While other organisms can, it takes a whole complicated set of interacting genes that E. Coli lack. Could E. Coli, by random chance, mutate such a family of genes? How long, how many and how many generations of bacteria would it take?
In 1988, cultures of E. Coli were started in media with little sugar, but much citrate. Any bacteria that could eat citrate would have a huge selective advantage. After 31,500 generations, one colony finally gained the ability to eat citrate. Going back to the freezer, and looking at the earlier colonies frozen back, it became clear that the pieces started to come together in parts at around 20,000 generations.
What an amazing finding! Just by being in a selective environment, that rewarded bacteria that could learn to do a complex new task, the part could form by a series mutations and eventually be selected for. Exactly as evolution would predict–an elegant demonstration of both halves of evolution, natural selection and the arising of complex traits by random mutation. It’s a stinging slap in the face of the Intelligent Design creationists, whose entire loudly touted faith-system is based on the impossibility of this event.