In 1833, John Obadiah Westwood, a British entomologist, tried to guess how many species of insects there are on Earth. He extrapolated from England to Earth as a whole. “If we say 400,000, we shall, perhaps, not be very wide of the truth,” he wrote. Today, scientists have found over a million species of insects and keep finding more every year.

The question of how many species there are on Earth has been a tricky one ever since Westwood’s day. I’ve written a story for the New York Times about a new estimate that was published today: 8.7 million.

Continue reading “How many species are there? My latest for the New York Times” →

In the wake of last year’s earthquake in Haiti, cholera arrived on the island for the first time in 60 years.According to the World Health Organization, 419, 511 Haitians got sick with cholera as of July 31, of which 5,968 died. The infection rate is dropping right now, but the arrival of Hurricane Irene could change that.

As I wrote in December, scientists applied evolutionary biology to find clues to how cholera–or, more precisely, the bacteria Vibrio cholerae— came to Haiti. They compared the DNA in the strain in Haiti to ones that have been found in other parts of the world. From this analysis, they drew a tree, which I’ve reprinted below.

Continue reading “Zooming In On the Cholera Tree of Life (And Death)” →

I hate to say I told you so.

A few months ago I was asked to give a couple talks to the skeptic community. Since I had just published a book about viruses, I decided to talk about the way myths so often crop up around them, and how a properly skeptical person should think about viruses. Over the centuries, viruses have been encircled by urban legends, superstitions, and conspiracy theories. The name “influenza” dates back to a time when European physicians believed the flu was due to the influence of the stars. More recently, HIV has been subject to all sorts of myths, from stories that it was created by the CIA to claims that it is not the cause of AIDS. The autism-vaccine controversy has been fueled in part by myths about viruses–namely, that the risk from vaccines is far greater than the risk from viruses like measles.

Continue reading “Chronic Fatigue Syndrome: Death threats for scientists?” →

It’s time to revisit that grand old parasite, the brain-infecting Toxoplasma. The more we learn about it, the more marvelously creepy it gets.

Toxoplasma is a single-celled relative of the parasites that cause malaria. It poses a serious risk to people with compromised immune systems (for example, people with AIDS) and fetuses (which is why pregnant women need to avoid getting Toxoplasma infections). If you’ve got a healthy immune system, it doesn’t cause any immediate harm. (Ed Yong has explained why a purported link to brain cancer is very weak.) All told, perhaps a quarter or a third of all people on Earth carry thousands of Toxoplasma cysts in their heads. Most never become aware of their living cargo.

Continue reading “Fatal Attraction: Sex, Death, Parasites, and Cats” →