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Live Fast, Die Young?

Why do some animals have longer biological life spans than others? Size often is a key factor. In general, larger species within the same group (mammals, reptiles, amphibians, etc.) live longer than their smaller cousins. At the most, for example, a tiny spring peeper treefrog may live three to four years, while a bullfrog can live a decade and a half. At 4 years old a little bluntnose minnow is elderly, while a largemouth bass is barely middle-aged. Large mammals tend to be proportionately long-lived (elephants, up to 80 years, whales a century or more) while the lives of small mammals often are fleeting (a year for an average chipmunk).

The reason? Smaller creatures have faster metabolisms. Their hearts beat faster, they breathe more rapidly, their cells burn energy at a higher rate to keep their bodies warm and nourished — so the little animals tend to wear out sooner. In its brief lifetime of a few years, a mouse’s heart will beat as many times — or a bit more — than a 69-year-old elephant’s: roughly 1 billion. It’s as though small animals’ bodies zip through their lives on fast forward.

These small-versus-large, live-fast-die-young principles don’t hold consistently true, however. Small dogs, for instance, generally live longer than large dogs. An African lion’s 14-year average life span is roughly that of a household cat. And one of nature’s fastest-burning metabolic fireballs — the ruby-throated hummingbird (above) — can live nearly a decade, about twice the average life span of a waddling woodchuck.

The reasons behind nature’s wide-ranging life spans, it seems, are — like life itself — varied and uncertain.

Read about Real vs. Ideal Life Spans, and discover the ages of the longest-lived plants and animals.

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