How many species are there, really?
|May 24, 2011||Posted by News under speciation|
In “Rewriting the textbooks: Noah’s shrinking ark” (part of a series on stuff in the textbooks that could use an airbrush), Kate Douglas (New Scientist, 23 May 2011) tackles the tangled problem of species, supposedly standing at 30 million, which she describes as “almost certainly a huge overestimate.” So not much is systematic apart from the names.
Last year, Andrew Hamilton at the University of Melbourne, Australia, and his colleagues took all these factors into consideration in a new statistical analysis based on beetle counts in 56 species of tree in Papua New Guinea. They came up with a far lower figure for the arthropods – just 2.5 million species or thereabouts (American Naturalist, DOI: 10.1086/652998).
Multiply this by three, and you come to a total of fewer than 8 million species. Hamilton goes even lower, arguing that vertebrates and plants have been more thoroughly catalogued than tropical arthropods. “The magic number is 5.5 million,” he says (New Scientist, 12 June 2010, p 4).
Why does it matter? Darwinian evolution depends on speciation, so over-readiness to claim that a new species has evolved inflates the claims for Darwinism. More immediately critical from a public policy perspective, environment legislation typically hinges on issues around the extinction of species – but we need to be sure that the species is distinct enough to go extinct.