David Secko | Nov 7, 2004 | 5 min read
Marine threespine sticklebacks haven't morphologically changed in an estimated 10 million years, but their freshwater offshoots show no signs of slowing down. These 5-cm-long, freshwater fish have undergone a recent evolutionary change, variably losing their calcified body armor and retractable pelvic and dorsal spines. Remarkably, isolated marine and freshwater sticklebacks can be hybridized in the laboratory, a fact that is allowing researchers to analyze the genetics behind their natural dive