Everything Science Forum

Size Matters: The Hidden Mathematics of Life
http://www.npr.org/templates/story/story.php?storyId=12877984

Weekend Edition Saturday, August 18, 2007 · Size matters.

Giant turtles, elephants and blue whales move through their lives with a slow grandeur that seems very different from littler creatures. Watch a hummingbird dart through a garden, or hold the smallest mammal, a little mouse-like shrew in your hand and you can feel it trembling with a feverish energy.

Compare an Elephant to a Teeny Shrew

Though big and little creatures look very different, below the surface there is a surprising unity. Biologists have compared the heartbeats of mammals and discovered that on average (this won't apply to any individual, just to groups) elephants and shrews and most of the critters in between have a limit of about a billion and a half heartbeats in a lifetime and then they die.

The reason an elephant lives longer than a shrew is not because its heart beats longer. It's because its heat beats slower. So it takes a few more years for the elephant to complete his or her up to one and a half billion beats.

Now comes the subtler question: Why do big things use up energy more slowly?

. . . .