Michael Desai of Harvard University is testing the life cycle of baker’s yeast. every 12 hours. He uses robots to remove the fastest-growing yeast in each colony, selecting the fittest to live on, and discarding the rest.
The test has been ongoing over the course of 500 generations.
“His experiment, which other scientists say is unprecedented in scale, seeks to gain insight into a question that has long bedeviled biologists: If we could start the world over again, would life evolve the same way?”
After 500 Generations The Answer Is:
>No matter the path taken, all colonies ended in the same evolutionary outcome.
>Desai found that early mutations influence future evolution, shaping the path the yeast takes. But in Desai’s experiment, that path didn’t affect the final destination. “This particular kind of contingency actually makes fitness evolution more predictable, not less,” Desai said.
Scientists don’t know why all genetic roads in yeast seem to arrive at the same endpoint, a question that Desai and others in the field find particularly intriguing.
>“Perhaps there is another layer of metabolism that no one has a handle on,” said Vaughn Cooper, a biologist at the University of New Hampshire who was not involved in the study.
It’s also not yet clear whether Desai’s carefully controlled results are applicable to more complex organisms or to the chaotic real world, where both the organism and its environment are constantly changing.
>“In the real world, organisms get good at different things, partitioning the environment,” Travisano said.
>I’m not exactly sure why this is surprising. Claims that early mutations might lead to significantly different life don’t include the condition that the environment is static for that entire time. You should expect that static environments have a steady state solution. Getting an ensemble average of steady state (or near steady state) solutions and finding that their standard deviation is small isn’t surprising.
I think the idea is that mutation Mx might come about which is selected for due to environment E1 which later leads to Mx2 = Mx+dM which is selected for by E2 = E1+dE.
If the original mutation is My instead of Mx, you might expect it would be the path of least resistance to go to My2 = My + dM instead of somehow achieving Mx and then adding on another dM to deal with with E2. As long as mutations x and y are selected for in their universe there is no reason to expect them to converge.
That is… unless you have a petri dish that is only ever in Environment E1 and you run the experiment for ages and ages allowing both Mx and My (and thousands of other mutations) to pop up and compete against each other over and over. Then, yes, of course, you expect there to be some ‘fittest’ mutation that fits E almost perfectly that will eventually develop and become predominant.