Evolution in the Lab
It is often claimed that evolution is not a science because it cannot be reproduced in the laboratory. In fact, however, as we discussed at Boskone, evolution is now a laboratory science–and a growing tool of industry.
The most famous example of experimental evolution is the domesticated silver fox bred from wild foxes by Russian scientists starting in 1959. Dmitri Belyaev began this amazing experiment, continuing through adverse political conditions up till the present day, now directed by Lyudmila Trut. In the experiment, wild foxes were selected for “low flight distance” — that is, how close you can get to the animal before it runs away. Animals selected on this basis over generations resulted in descendents with many of the traits and behaviors found in tamed dogs, such as low adrenaline production, raised tail, and floppy ears, as well as foreshortening of limbs typical of “neoteny,” the retaining of juvenile appearance. DNA chip experiments now show that certain brain genes have changed between the wild and domesticated foxes.
In another interesting experiment, mice were selectively bred for “high voluntary wheel running.” These High-Runner mice turned out to differ in their response to dopamine, resembling aspects of ADHD. One wonders, though, whether selection of this particular trait says more about the culture of today’s researchers.
The most advanced form of laboratory evolution involves breeding of bacteria–Richard Lenski’s famous experiment tracking 50,000 generations of E. coli. For this experiment, E. coli bacteria were put in fresh glucose medium every day, growing up for several generations, then diluted again. Every 75 days, cultures were frozen away–something you cannot do with dogs or mice. And all the sample genomes could be sequenced, thanks to today’s mammoth DNA sequencers. So, in addition to the descendents, you can track the history of every diverging line of cells.
The E. coli experiment produced all kinds of fascinating observations. For example, cells fed on this rather limited diet gradually increased in size (over the generations). Size increase is interesting because it happens so often in animals, such as the evolution of horses. Alternatively “mini” animals evolve, too. So by studying E. coli we may gain clues as to general principles of evolution of size. Another cute result–one line of descent evolved to eat the citrate buffer instead of the glucose. Tracking back the history reveals other lines that independently evolved this “new” trait. The experiment was impressive enough to earn condemnation by Conservapedia.
Today, what we call adaptive laboratory evolution has become the tool of choice for industrial development of new producer strains of cloned products. Where do you think evolution will go next?