Time traveling
Many thanks to Yonatan Zunger for sharing this seemingly simple but important research. Dr Lenski, an evolutionary biologist, has looked at natural selection in an unnatural way. He’s looked at 60,0000 generations of E. Coli. He saves every 500th generation in a -80°C freezer, which can be reanimated at any time, to compare generations.
In cancer research, tumor cell lines from patients are often grown in media and used in in vitro and in vivo research. What Dr Lenski’s experiment shows, is relevant to cancer research, i.e., how close is your cell line to the “parent” or original cell line. The results of a new drug experiment could be compromised if the cell line is different than the cells that were originally taken from the patient.
#SciecneSunday
Originally shared by Yonatan Zunger
60,000 generations of people ago, Homo Erectus was walking around in Asia. It’s deep enough in time that evolutionary changes on this scale are no longer subtle, but obvious — but also deep enough in time that we can only examine it through archaeology. But what if we could replicate this in the lab?
Richard Lenski of Michigan State University has come up with a way to do just that: using E. coli, whose generations are far shorter. When the experiment began in 1988, he placed twelve genetically identical single cells of E. coli (they reproduce asexually, so you don’t need a large starter population) in twelve petri dishes, and exposed them to a particular, predictable environment that they weren’t used to: 6 hours of food, followed by 18 hours of starvation, every day.
Every 500 generations, a sample from each of these twelve lines was frozen. (E. coli takes well to freezing; they just stop doing anything until they’re thawed)
This past April, they passed the 60,000-generation mark. All twelve lines changed to grow faster during flush times and to have larger cells — reasonable adaptations to their environment — but the details in each line varied.
Experiments like these let us really understand the effects of chance on evolution, the speed at which traits can evolve, and so on. This isn’t obvious because evolution, especially in asexually reproducing creatures, works by a “random ratchet:” each generation may have some small differences from the last (how many? Are some kinds of differences more likely than others?) and this may or may not help the individuals survive and thrive. (But will that individual encounter circumstances where their particular genetic heritage is a help or a hindrance? Or will they simply get eaten randomly before they can reproduce, thanks to something unpredictable?) Selection pressures mean that genes better adapted to the situation on the average will spread more than genes less adapted to the situation, but without real experiments like these — in incredibly simplified and controlled situations like a fixed environment and an asexual species — we can’t get a good handle on how quickly things can adapt.
There are many more deep-time experiments which would be interesting to do, and the possibility of exploring tens of thousands of generations within a few decades makes it possible, although not easy. What would the speed be like if they could reproduce sexually, swapping traits? What would happen if half the lines were placed in one environment, and half in another — could we clock the rate at which the lines diverged?
Sometimes, science requires patience.
via gwern branwen.
http://blog.longnow.org/02014/08/21/lenski-long-term-evolution-experiment
