Here's a fascinating science story: since the clean-up of the once foully polluted Lake Washington here in Seattle, the threespine stickleback of Lake Washington has been forced to "evolve backwards" in order to cope with their changed environment. Lynda V. Mapes, reporting on a paper to be published in the May 20 issue of Current Biology, writes:
Just five decades ago, Lake Washington was notoriously polluted, full of murky water festering with blue-green algae that thrived on the millions of gallons of raw sewage the cities pumped into it.
Pollution cut visibility in the water to only about 30 inches. And that was great for the stickleback, a rugged looking customer with three sharp spines along its back, because it easily could hide in the murk from its primary predator, cutthroat trout.
Enter a $140 million cleanup of the lake, launched in the 1960s, at the time one of the biggest pollution-control efforts in the nation. Today, Lake Washington is swimmable again, and visibility reaches 25 feet.
Lovely for people — treacherous for the stickleback.
But to their surprise, researchers have discovered that in the space of four decades, the stickleback evolved backward, to an earlier version of the species that had full-body plating.
The change in visibility allows cut-throat trout to see and prey on the threespine stickleback. You can read more here.