In other words, one kind of pupfish changed into another kind of pupfish when placed in the particular environment of the other. Significant adaptive variations appeared within two years. Since pupfish reach full maturity within 2 to 3 months and spawn from late February through the summer, that’s about four or five pupfish generations. “No new information had appeared in the guppies’ DNA; instead, the expression of the existing information had altered.”
Go read the details– it’s just too cool!