Why does every mammal get 1 billion heartbeats in their life? | Veritasium

The Gist

Virtually all mammals share approximately one billion heartbeats over the course of their lives because metabolic rate scales sublinearly with mass. While a tiny shrew beats its heart 1,200 times per minute and lives for a year, an elephant beats its heart 30 times per minute and lives for decades, landing both on nearly the exact same lifetime total.

Quick Overview

Virtually all mammals accumulate roughly one billion heartbeats in a lifetime because metabolic rate scales to mass raised to the three-quarters power rather than linearly. This mathematical principle, known as Kleiber's Law, emerges from the fractal geometry of space-filling internal transport networks like circulatory systems. Biologists, mathematicians, and physicists spent centuries debating scaling exponents across biology and urban planning, discovering that cities and organisms obey surprisingly similar power laws.

Key Points: Researchers once injected an elephant named Tusco at the Oklahoma City Zoo with 300 milligrams of LSD, which caused him to trumpet, collapse, and die within five minutes. The deadly mistake in the elephant LSD experiment was assuming that safe drug dosages scale linearly with mass rather than metabolic rate. An Etruscan shrew and an African bush elephant both log roughly one billion heartbeats between birth and death despite their massive difference in size and lifespan. Kleiber's Law dictates that metabolic rate scales with mass raised to the three-quarters power, meaning animals do not burn energy in direct proportion to their weight. West, Brown, and Enquist formulated WBE theory in 1997, arguing that space-filled fractal distribution networks with invariant terminal units explain the three-quarters power law. Humans have successfully defied biological scaling by increasing our expected lifetime heartbeats to nearly three billion through better sanitation, germ theory, and medical advancements. Cities follow identical power laws where urban indicators like wages, patents, and crime scale superlinearly with population due to social networking benefits.