An interesting theory claims that a lifespan for every living creature is equivalent to about 1 billion heartbeats (in average). The theory is based on the correlation between metabolic rate (heart rate) and size of the species. Thus, referring to this claim, animals including humans have about 1 billion heartbeats to use up before they expire.
While many people questioned such a vague assertion, San Jose State University has provided an animal longevity and scale chart to support the “1 billion heartbeats” theory. The chart encompasses various species of different sizes.
As indicated in such representation, humans do have the biggest number of heartbeats above all other creatures, with an overall 2.21 billion heartbeats in a lifetime. The number specifically applies to those weighing 90 kilograms or 90000 grams, and whose average heart rate is at 60 per minute. Humans with this heart rate are thought to live about 70 years.
Next to humans are chickens, with 2.17 billion beats total, for those that weigh 1500 grams and heart rate is at 275 per minute – longevity is 15 years. Meanwhile, cats with a heart rate of 150 per minute and weigh 2000 grams do have 1.18 heartbeats to complete their lifespan of 15 years. In this respect, chickens and humans are both outliers as they live more than double as their heart rates would show.
So, why does the number of heartbeats are roughly the same while their life spans differ? Say for instance, the average life span for humans is 70 years, while cows have 22 years and 10 years for ducks.
As explicated in pertinent studies before, as the creature gets bigger, its pulse rates slow down. As the pulse rate decelerates, life span further extends. Other factors affecting such variation are also expounded through a meticulous mathematical principle referred to as “quarter-power scaling.” It is also backed with certain scientific measurement depicted by the Kleiber Ratio, which tackles the exquisite inter-connectivity between metabolic rate and mass of every living creature.