A seminal paper by Norman Myers in 1988 first identified ten tropical forest "hotspots" characterized both by exceptional levels of plant endemism and by serious levels of habitat loss. In 1990 Myers added a further eight hotspots, including four Mediterranean-type ecosystems. Conservation International adopted Myers' hotspots as its institutional blueprint in 1989, and in 1996, the organization made the decision to undertake a reassessment of the hotspots concept, including an examination of whether key areas had been overlooked. Three years later an extensive global review was undertaken, which introduced quantitative thresholds for the designation of biodiversity hotspots:
To qualify as a hotspot, a region must meet two strict criteria: it must contain at least 1,500 species of vascular plants (> 0.5 percent of the world's total) as endemics, and it has to have lost at least 70 percent of its original habitat.
In the 1999 analysis, published in the book Hotspots: Earth's Biologically Richest and Most Endangered Terrestrial Ecoregions, and a year later in the scientific journal Nature (Myers, et al. 2000), 25 biodiversity hotspots were identified. Collectively, these areas held as endemics no less than 44 percent of the world's plants and 35 percent of terrestrial vertebrates in an area that formerly covered only 11.8 percent of the planet's land surface. The habitat extent of this land area had been reduced by 87.8 percent of its original extent, such that this wealth of biodiversity was restricted to only 1.4 percent of Earth’s land surface.
A second major reanalysis has now been undertaken and published in the book Hotspots Revisited. This website has been completely updated with the results of this analysis, and details of this study can be found in Hotspots Revisited and Key Findings.