If you've ever wondered how quickly evolution works, well, now you have an answer: slowly. Very. Slowly. In fact it takes at least 24 million generations for a mouse-sized animal to evolve to the size of an elephant.
The research, published in the Proceedings of the National Academy of Sciences, looked at the timescales involved in species growth and shrinking due to evolution. Turns out, it's much speedier to get small. The study suggests it takes just 100,000 generations for very large decreases, such as those that lead to dwarfism.
But how the hell do you work out how long it takes for a mouse to turn into an elephant? Largely through comparison and extrapolation. The researchers, from Monash University, looked at 28 different groups of mammals, including elephants, primates and whales, over the past 70 million years. They tracked the changes in size by generation in order to make the results comparable across the data set. Amusingly, mammals that live in water grow quickest, because its "easier to be big in the water," according to Dr Erich Fitzgerald, one of the researchers.
The reason it's quicker to shrink as you evolve? It's preferable. "You need less food and can reproduce faster, which are real advantages," explains Dr Alistair Evans. Being small isn't all bad, then. [PNAS via Science Daily]