Photo by: Getty Images

Getty Images

Almost Every Mammal Gets About 1 Billion Heartbeats

By: Reuben Westmaas

You only have a limited number of heartbeats in your life.

August 01, 2019

It's strange to think that you have a limited number of heartbeats in your life, but at least you can take some solace in the fact that no one can ever say how many exactly you'll get, right? Wrong. Science knows. And it's about the same for almost every mammal.

Same Song, Different Tempos

Rabbits live about three years. Elephants can get up into their 80s. But both of them get about one billion heartbeats in their lifetime. It's just that elephant hearts beat a lot slower. As it turns out, that number stays (roughly) the same across other species of mammals. You might also have noticed that elephants are slightly larger than rabbits are, and there seems to be a similar correlation between size and lifespan. Is this indicative of a deeper truth of biology? Or even of the universe? It just might be — but more on that in a moment.

Before we get into the really head-trippy stuff, let's talk about the exceptions to the rule. Thanks to modern medicine, food preservation technology, and our habit of purifying our water sources, human beings have been able to extend our hearts' lives far past the one billion limit. We get a little bit more than two billion heartbeats in our lives, and who knows? In the future, we might be able to push it up to three.

Living at Large Scales

In 1999, physicist Geoffrey West and biologists Jim Brown and Brian Enquist found unexpected, interdisciplinary common ground when they set out to find how exactly animals' energy use and needs scale as they get larger or smaller. There'd been a fair amount of research into this already — in the 1930s, biologist Max Kleiber penned what's known today as "Kleiber's Law": metabolic rates scale to the three-quarter power instead of increasing at a one-to-one ratio. This is a bit complicated, but stay with us. Basically, it means that a cat, which is 100 times larger than a mouse, does not use 100 times the energy that a mouse does. Instead, it requires 1003/4 times the energy of a mouse — and that's only about 31.6 times the mouse's requirements.

But what this trio of scientists wanted to discover was far more complex than mere metabolism rates. They wanted to find out how characteristics such as lifespan and pulse rate scaled as well. Those features didn't have the exact same rate as metabolism, but they clearly correlated with each other. Lifespan tended to scale to the power of one-quarter, and heart rate at the power of negative one-quarter. In other words, there's a mathematical equation that lets you predict exactly how long an animal will live and how fast its heart will beat, based on its size.

This article first appeared on Curiosity.com.

Next Up

The “Lungs of Our Planet” are Under Threat

World Rainforest Day is June 22, bringing awareness and action to save these precious ecosystems. But if the current rate of deforestation continues, will there be any rainforests in 100 years?

The Stegosaurus Was An Ancient Relic To The T. Rex

These two popular dinosaurs never crossed paths.

Nearly 500 Million Animals Have Been Lost in Australia’s Wildfires

The wildfires in Australia continue to spread across the country—destroying homes, forests, animals, and anything in its path.

Cows Kill More People Than Sharks

Sharks are the least of your problems according to these statistics.

Why Islands Have the Most Beautiful and Unique Creatures on Earth

Places like New Zealand, Austrailia, Hawaii, and the Galapagos give us major wanderlust. But what is it about islands that make scientists weak in the knees?

These 5 Mythical Animals Turned Out to Be Real

Many animals people once believed these animals were imaginary.

Saving the World’s Gibbons Monkeys

Gibbon monkeys, who live in the evergreen tropical rainforests of Southeast Asia, are the most endangered primate species in the world.

How the Mediterranean Became a Corridor of Death for Birds

Across the world, the bird population is thinning due to illegal poaching and habitat loss, especially in Europe and Africa during migratory seasons. Conservation groups globally are trying to protect our nearly extinct feathered creatures.

Why Islands Have The Most Unique Creatures on Earth

What is it about islands that makes scientists weak in the knees?