My question is, why would cells 'suddenly' change instead of a gradual change over time, as Darwin suggested?
Sudden climatic change?
"Environmental upheaval causes genes to mutate,"
Never mind.
Need to read more thoroughly instead of stopping on certain 'points'.
:0(
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.