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We refer to this as experimental evolution.

We subject bacteria to different selection pressure parameters.

project them through bottlenecks.

Every day, we randomly collect a handful of bacteria from the flask, put them in a new fresh environment with fresh food, keep them in this environment for 24 hours until they reach a more dormant state, and then we...

introduced them to a new environment.

So we repeated this for about, I will say, 150 days.

So every day, nonstop, we repeated this experiment.

We kept the environments to the same, because we had different initial conditions.

We kept the environment constant, same temperature, same food, same source of carbon.

But we created replicates for each environment.

So in some ways, we created our own fossil record in the lab by evolving and generating these flasks.

And every step of the way, we also froze these cells and took stocks of them in the cryo-freezer.

For E. coli, it's usually 20 minutes.

It's the same way.

So we introduced variation at the elongation level because we perturbed it with different elongations.

We found that if we introduce a different protein that is very different, the cells don't like that, right?

So if the distance is larger, the...

consequences also large, meaning that you hit them harder if you introduce a variant that is really foreign to them, that's really distant.

In our case, it was the ancestor.

They really did not like the ancestor, but they were okay with their nearest cousin.