Sydney: It would take at least 24 million generations for a mouse-sized creature to evolve into something as big as an elephant.
Conversely, it would require only 100,000 generations for very large creatures to regress into dwarfs, says the first ever computation of large scale evolution mammals.
The computation, led by Alistair Evans of Monash University, describes increases and decreases in mammal size following the extinction of the dinosaurs 65 million years ago, the journal Proceedings of the National Academy of Sciences reports.
Evans, evolutionary biologist from Monash School of Biological Sciences, led a team of 20 biologists and palaeontologists which made the discovery.
Evans said the study was unique because most previous work had focused on micro-evolution, the small changes that occur within a species, according to a Monash statement.
"Instead we concentrated on large-scale changes in body size," said Evans. The paper looked at 28 different groups of mammals, including elephants, primates and whales, from various continents and ocean basins over the past 70 million years.
"The huge difference in rates for getting smaller and getting bigger is really astounding - we certainly never expected it could happen so fast," Evans said.
"When you do get smaller, you need less food and can reproduce faster, which are real advantages on small islands," Evans said.