SCRIPT: Living larger, living longer
Our world has seen some big animals come and go: from the enormous dinosaurs that roamed Earth millions of years ago, to the massive mammals of today. Aside from the size connection, something else links these giant animals – the length of their lives. The basic fact is that the bigger the animal, the longer they live.
Let’s start with dinosaurs. No one knows for sure, but it is thought that some of the bigger dinosaurs lived for between 70 and 300 years – extraordinarily long life spans compared to most much smaller animals alive today. These estimates are based on measurements taken from modern day relatives of the dinosaurs, that is, large reptiles like alligators that have a life span of around 60 years.
What about our modern day giants? Elephants are known to live for around 70 years, and larger whales for between 70 and 80 years. We also have additional information about animals existing today that we don’t have about dinosaurs, for example, heart rate. And the speed at which the heart beats seems to be linked to life span. An elephant’s heart beats around 30 times per minute. Large whales have heartbeat rates of around 20 per minute. The connection becomes much clearer when we compare these massive animals with smaller ones. A cat’s heart beats around 150 times a minute, and its average life span is around 15 years. A rabbit’s heart beats around 200 times a minute, and these animals have an average life span of nine years. Lastly, let’s think about the tiny hamster whose heart hammers away over twice as fast as even the rabbit’s, at 450 beats a minute. A hamster’s average life span is three years.
So what can we conclude? The general theory, though certainly with some exceptions, is that the life span of a species is connected to the speed at which the heart beats. Animals can be bigger, smaller, faster, slower, or more or less intelligent. However, the number of times the heart of most species beats is approximately the same over the course of a lifetime … that is up to 1.5 billion times. Therefore, larger animals live longer, not because their hearts beat more, but because their hearts beat more slowly.
This theory applies to humans too, although we have managed to live beyond expectations. Thanks to our understanding of the world, for example, our knowledge of the need to drink only clean water and of how to protect ourselves from illness, humans have managed to improve the life span that nature predicted for us based on our size and an average heart beat of around 60 beats per minute.