Writing about science means looking up a lot of numbers. Trying to find a figure for the number of cells in the body or the protein-encoding genes in human DNA or patients diagnosed with ovarian cancer from 1980 through 1995 can eat up a lot of time and internet bandwidth. For some of these oft-cited numbers, there’s a mutually agreed upon estimate that science writers can drop into the articles, such as the 23,000 usually tossed around for the number of human genes. But it’s worth remembering that these figures are subject to change – after all, it was thought as recently as 10 years ago that there were 100,000 genes in human DNA.
A new counting kerfuffle broke out this week for yet another oft-cited scientific figure: the number of species on Earth. Last year, zoologist Robert May proposed in Science that the human race would be “embarrassed” should aliens show up tomorrow and ask how many different types of organisms live on our planet. Depending on the model used, one could argue for a number anywhere between 3 and 100 million eukaryotes, May wrote – and that doesn’t even count viruses and bacteria, which far outnumber the larger species.
But as the authors of the PLoS Biology article “How Many Species Are There on Earth and in the Ocean?” found out this week, picking a number within that range is hazardous territory. Using a mathematical model based on the roughly 1.2 million species we currently know about, the research team calculated a new estimate: approximately 8.7 million species from land and sea. Of those, only 14% of land species and 9% of sea species have so far been cataloged by humans, the authors concluded, and describing those remaining could take over 1,000 years and $364 billion. “Our results also suggest that this slow advance in the description of species will lead to species becoming extinct before we know they even existed,” they wrote.
Dramatic stuff, but what about the math? In Carl Zimmer’s article on the study for the New York Times, the first bubbles of discontent can be felt around the biology world, from fungi experts to entomologists who argue that the 8.7 million number is far too low. Scientists who study microbes were even less pleased with the mathematical model, which they said dramatically under-counted their favorite species. On his blog, Phylogenomics, microbiologist Jonathan Eisen pish-poshed the paper’s estimates of 10,000 prokaryote species: “I think without a doubt the number of bacterial and archaeal species on the planet is in the range of millions upon millions upon millions. 10,000 is clearly not even close.” Two other microbiologists wrote a letter to the Washington Post, pointing out that “a teaspoon of soil contains more than 10,000 species of bacteria.” For the time being, it looks like our alien visitors will have to be satisfied with the answer, “Lots.”
Speaking of the importance of bacteria and microbes, consider the discovery of antibiotic-resistance genes in 30,000-year-old bacteria from the Yukon Territory. Though these bacteria lived approximately 29,930 years before the discovery of penicillin, they possessed defenses against the naturally-occurring weapons scientists have seized upon to develop infection-fighting drugs. That long history means outsmarting drug-resistant bacteria may be even harder than scientists thought, and makes the case for even more selective use of antibiotics. “Bacteria share these genes like baseball cards with each other,” Stuart Levy at Tufts University told Nicholas Wade of the New York Times.
Has an important culprit in amyotrophic lateral sclerosis, aka Lou Gehrig’s disease, been discovered? The Medical Center’s Raymond Roos comments on a recent Northwestern University study.
On the blog, we’ve covered the link between sleep loss and testosterone, weight gain, and blood sugar. A new study from UCSD and Harvard now finds a connection between sleep quality and blood pressure. Our sleep research guru Eve Van Cauter commented on the research for TIME.
Just another reminder to check out the Medical Center’s new Facebook page, where this week you can find articles from the blog, information on the DNA Discovery Lab at the Field Museum, and President Sharon O’Keefe’s letter to the editor on hospital charity care. If you like it, please hit that “like” button!