Santa Fe Institute

Mouse to elephant: Species shrink at faster rates than they grow

Jan. 31, 2012 2:27 p.m.

Two SFI researchers are among an international team of scientists asking how fast mammal species have grown since the dinosaurs, how fast some species have shrunk, and why.

Their work shows it took about 10 million generations for terrestrial mammals to hit their maximum mass, and that it took only about 100,000 generations for very large body mass decreases to occur.

“Our work demonstrates, for the first time, how quickly the major changes in body size have happened in the history of mammals,” says Alistair Evans, an evolutionary biologist at Monash University (Australia) who led the team of 20 biologists and paleontologists. SFI External Professor James Brown and SFI Postdoctoral Fellow Marcus Hamilton collaborated on the paper.

“Most previous work has focused on microevolution, the small changes that occur within a species,” Evans points out. “Instead we concentrated on large-scale changes in body size. We can now show that it took at least 24 million generations to make the proverbial mouse-to-elephant size change – a massive change, but a very long time.”

The research team looked at 28 different groups of mammals from the four largest continents (Africa, Eurasia, and North and South America) and all ocean basins for during the last 70 million years. These groups included elephants, rhinos, hippos, carnivores and whales.

Read the paper in PNAS (January 30, 2012)

Read the Monash University news release (January 30, 2012)

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