Article of the week: The tropics as cradle and as museum

David Jablonski, Kaustuv Roy & James W. Valentine, Out of the Tropics: Evolutionary Dynamics of the Latitudinal Diversity Gradient, 314 Science 102 (2006), DOI: 10.1126/science.1130880:

The evolutionary dynamics underlying the latitudinal gradient in biodiversity have been controversial for over a century. Using a spatially explicit approach that incorporates not only origination and extinction but immigration, a global analysis of genera and subgenera of marine bivalves over the past 11 million years supports an "out of the tropics" model, in which taxa preferentially originate in the tropics and expand toward the poles without losing their tropical presence. The tropics are thus both a cradle and a museum of biodversity, contrary to the conceptual dichotomy dominant since 1974; a tropical diversity crisis would thus have profound evolutionary effects at all latitudes.

Dan Whipple's summary of this article cuts to the chase:

In the tropics, which wrap around swaths of nearly every continent, animal and plant diversity is abundant, and it declines as one moves toward the North and South poles. Why this difference? Many evolutionary biologists favor one of two explanations: Either the tropics are where most new species originate, or species are less likely to go extinct there than elsewhere. New research suggests that both are true. The finding indicates that the tropics drive biodiversity and that extinctions there may have especially devastating effects.

See also Charles R. Marshall, Fossil Record Reveals Tropics as Cradle and Museum, 314 Science 66 (2006), DOI: 10.1126/science.1133351.