Discover, October 1, 1996

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Is natural selection the prime mover behind evolution? Darwin’s great insight into the mechanics of evolution was that a population of creatures always has a lot of variation–more feathers here, less fat there, more urge to kill there–and some of these variations allow the individuals bearing them to thrive and have more offspring than others. After many generations these traits become more common among the population as a whole. If one imagines fitness as a beckoning peak on a given ecological landscape, then natural selection should be a process that moves species steadily uphill.

Continue reading “Natural Detours” →

Discover, August 31, 1996

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Jeffrey Bada’s lab are nondescript but far from ordinary. They come from a crater near Sudbury, Ontario, that formed 1.85 billion years ago, when a meteorite the size of Mount Everest slammed into Earth. Canadian geologists sent the rocks to Bada, a geochemist at the Scripps Institution of Oceanography, to see if they contained any organic carbon molecules. Not likely, Bada thought: if the molecules hadn’t been incinerated on impact, they would have been destroyed–probably by hungry microbes–long ago. Bada put the rocks on a shelf for a few years.

Continue reading “Buckyballs from space” →

Discover, May 1, 1996

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Monarchs fly a multigenerational circle around the eastern United States every year. In the fall the last generation heads for Mexico.

When we think of the great animal migrations, we tend to think of great animals–creatures like caribou or wildebeests. But one of the most spectacular movements of life is undertaken by the four-inch-wide monarch butterfly. Every fall tens of millions of monarchs disappear from the United States. Until the mid-1970s, no one knew where they went; it was only then that an amateur lepidopterist found their hiding place in a high mountain range in Mexico.

Continue reading “The Flight of the Butterfly” →

Discover, March 31, 1996)

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When our vertebrate ancestors debuted about 520 million years ago, they didn’t take the world by storm. Inches long and jawless, they grabbed helpless worms with their lips, much as a toothless, armless man might eat a hot dog. Only when fish developed jaws 460 million years ago did Earth see serious predation. “As soon as jaws evolved, there was a revolution,” says Jon Mallatt, a zoologist at Washington State University. “You got all these giant-jawed vertebrates that were at the top of the food chain and eating really big things–just mean, nasty carnivores all of a sudden. And one of these groups gave rise to the land vertebrates. So jaws were a big event. Without them we wouldn’t be here.”

Continue reading “Breathe before you bite” →

Discover, March 1, 1996

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Jaws may be nature’s version of a plowshares-to-swords program: They seem to have originally evolved to help fish breathe better.

When our vertebrate ancestors debuted about 520 million years ago, they didn’t take the world by storm. Inches long and jawless, they grabbed helpless worms with their lips, much as a toothless, armless man might eat a hot dog. Only when fish developed jaws 460 million years ago did Earth see serious predation.

Continue reading “Death From the Pleistocene Sky” →