The population was under dire circumstances. The strongest worms moved forward. I dont know the exact details at the gene level. But the worms where not happy with it. I can only speculate this is what happened. And I would expect DR. Fraser if you asked would not jump to this or any conclusion. In my experience, if a population is under pressure, you either evolve or die.
Take for instance, there was an experiment of lactose intolerant cells. They place these cells in lactose environment. These cells had no way to process this food source. What the cells did, was evolve, they somehow created the enzyme necessary to process the lactose. The cells where given a choice, either go extinct or evolve. They choose to survive.
So, I believe this was the same type of situation her. Its logical to think so..
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