[narby]

My question is, why would cells 'suddenly' change instead of a gradual change over time, as Darwin suggested?

The answer's in the article. Stress causes mutations, which are often recessive. But some time after the mutation, and the recessive gene is propagated through the population, it becomes more likely to double up and become the expressed gene in an individual, rather than the old dominant gene.

[Bigh4u2]

"But some time after the mutation, and the recessive gene is propagated through the population, it becomes more likely to double up and become the expressed gene in an individual, rather than the old dominant gene."

That makes better sense!

Sorta like a cancer, that may be dormant in your system for years, that suddenly appears.

Thanx.

[PatrickHenry]

Lots of neutral mutations occur, and they don't get selected in or out. They just persevere in the gene pool. Every now and then, a change in the environment makes such mutations advantageous to have. If they didn't exist, the species might go extinct -- most of them do. But sometimes, some of them may possess just the right characteristics (previously neutral mutations) for continued survival.