One day in 1788, students at the Hunterian School of Medicine in London were opening a cadaver when they discovered something startling. The dead man’s anatomy was a mirror image of normal. His liver was on his left side instead of the right. His heart had beaten on his right side, not his left.

The students had never seen anything like it, and they rushed to find their teacher, the Scottish physician Matthew Baillie, who was just as stunned as they were. “It is so extraordinary as scarcely to have been seen by any of the most celebrated anatomists,” he later wrote.

Continue reading “Growing Left, Growing Right” →

In the hearts of evolutionary biologists, mountains occupy a special place. It’s not just their physical majesty: mountains also have an unmatched power to drive human evolution. Starting tens of thousands of years ago, people moved to high altitudes, and there they experienced natural selection that has reworked their biology.

“This is the most extreme example in humans that you can find,” said Rasmus Nielsen, an evolutionary biologist at the University of California at Berkeley.

Humans have adapted to mountainous environments just as Charles Darwin predicted. To discover how this occurred, scientists are now examining the DNA of people who scaled mountains in different parts of the world.

Continue reading “Mountain Populations Offer Clues to Human Evolution” →

With the unofficial start of summer on Monday, many people will get up close and personal with the element that carries 17 protons.

I speak, of course, of chlorine.

Over the next few months, chlorine will ensure that countless swimming pools don’t turn into microbe-choked petri dishes. That’s only one of many uses we’ve found for the element. We sprinkle it on our food as table salt — a k a sodium chloride. We pump water through pipes made of polyvinyl chloride. Perchlorate, a combination of chlorine and oxygen atoms, fuels rockets and ignites fireworks.

Continue reading “Chlorine, Swimming Pool Helper, Has a Checkered Past” →

Imagine a wolf catching a Frisbee a dozen times in a row, or leading police officers to a stash of cocaine, or just sleeping peacefully next to you on your couch. It’s a stretch, to say the least. Dogs may have evolved from wolves, but the minds of the two canines are profoundly different.

Dog brains, as I wrote last month in The New York Times, have become exquisitely tuned to our own. Scientists are now zeroing in on some of the genes that were crucial to the rewiring of dog brains.

Their results are fascinating, and not only because they can help us understand how dogs turned into man’s best friend.

Continue reading “From Fearsome Predator to Man’s Best Friend” →

From North Carolina to Connecticut, billions of creatures with eyes the color of blood and bodies the color of coal are crawling out of the earth. Periodical cicadas are emerging en masse, clambering into trees and singing a shivering chorus that can be heard for miles.

What makes this emergence truly remarkable, however, is how long it’s been in the making. This month’s army of periodical cicadas was born in 1996. Their mothers laid their eggs in the branches of trees, where they developed for a few weeks before hatching and heading for the ground. “They just jumped out and rained down out of the trees,” said Chris Simon, a cicada biologist at the University of Connecticut.

Continue reading “17 Years to Hatch an Invasion” →