The Loh Down On Science

Changing Size

One pill makes you larger, one pill makes you small ...

This is Sandra Tsing Loh with the Loh Down on Science, saying, if only changing dress size were that easy!

Let's back up. For a mammal to evolve from the size of a rabbit to the size of an elephant takes ten-million generations! From mouse-sized to elephant-sized? Twenty-four million!

Or so says an international team of biologists and paleontologists. Using size data from the fossil record, they calculated rates of evolutionary size changes for various groups of mammals.

The record spanned seventy-million years, but species' life spans vary in length. So instead of counting the changes in years, the team counted them in generations, for easier comparison.

Oddly, size decreases were about ten times faster than increases. Probably because the decreases were cases of animals getting isolated on an island. That means they evolved with less competition for resources.

Also odd? Size increased faster in water than on land. Probably because water helps support larger bodies.

Thank you! Maybe now whales will finally stop saying it's a "glandular problem"! As if!



The Loh Down on Science, online, at lohdown.org. Produced by 89.3 KPCC and the California Institute of Technology, and made possible by TIAA-CREF.

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