Elephants Took 24 Million Generations to Evolve From Mouse-Size
Evolving bigger bodies takes longer than getting small, mammal study says.
Using both fossil and living specimens, scientists calculated growth rates for 28 different mammalian groups during the past 65 million years—and found that, for mammals, getting big takes longer than shrinking.
It takes a minimum of 1.6 million generations for mammals to achieve a hundredfold increase in body size, about 5 million generations for a thousandfold increase, and about 10 million generations for a 5,000-fold increase, the team discovered.
(See "Platypus Genome Reveals Secrets of Mammal Evolution.")
For land mammals, odd-toed ungulates—such as horses and rhinos—displayed the fastest maximum rates. Curiously, primates showed the slowest rates among the mammals examined.
"It's a bit of a mystery," said study leader Alistair Evans, an evolutionary