Fancy discovering a new species? It shouldn't be too difficult, as the best estimate yet of how many species the planet supports comes up at 8.74 million. Although about a quarter of those are in the sea, some 7.5 million species remain to be discovered.
Previous estimates varied wildly between 3 and 100 million. Camilo Mora of the University of Hawaii in Honolulu and colleagues say their figure is more accurate because it relies on a validated method consistent across well-catalogued forms of life such as mammals, birds and molluscs. For 18 of these groups, Mora's team worked out the numerical patterns by which they fan out hierarchically from phyla into classes, orders, families, genera and species.
Once they had established how these known groups radiate numerically, they extrapolated to less well-known groups such as fungi, enabling them for the first time to estimate with confidence the number of species in each hierarchy.
Some 86 per cent of land species and 91 per cent of marine species are yet to be found.