Evolution What the Fossils Say and Why it Matters

FIGURE 4.14. Evolution has happened in some groups over just a few decades. In the swift currents of Cedar
River, Washington, the sockeye salmon introduced in the 1930s have adapted so that the males can swim in
the strong currents and the females dig deeper nests in the sand to lay their eggs. But the salmon that invaded
the shallow waters of Pleasure Point in 1957 have developed rounder, deeper bodies in males to help fight
off rival males; the females dig shallower nests for their eggs because there are no strong currents. (Modified
from Weiner 2005)

Lake Washington

Pleasure Point Cedar River

16.7 inches 18.3 inches

5.6 inches Male 4.9 inches

Female

49.8ºF

42.8ºF

5 feet

3 feet

FIGURE 4.15. The three-spined stickleback fish also show rapid evolution. Species that live in the lakes or in
the ocean have longer spines that make it harder for a predator to swallow them. But sticklebacks living in
shallow streams have evolved shorter spines so predators like dragonfly larvae cannot catch them by their
protruding spines. (Photos courtesy D. M. Kingsley and S. Carroll)

Long spines

Reduced spines

Protect against

fish predators

Evade dragonfly

larvae predation