I stumbled across an article by Camilo Mora and others published last year in the journal PLoS Biology that takes a new approach at a very old question: How many species are there on Earth? We are only sure that the number is greater than the number of species that have been described, but beyond this we are woefully ignorant and our best guesses are wild, to say the least. The authors suggest that looking at the rate of discovery of higher taxonomic levels–family, class, order, etc.–tells us a lot about how many species we should expect to discover with continued exploration. The paper can be accessed here for free thanks for PLoS‘s open-access policy. It is a quick read and of interest to all biologists; while Bob May’s excellent perspective piece is a shining example of the way I would love to be able to write. It can be found here.