Who or what decides how long we live for? This is a question that has been debated for centuries. Do bigger animals live longer than smaller ones, or has it something to do with their diet? In 1883, Max Rubner posed the question; "Why do large animals and birds live longer than small ones?" Many theories have been put forward, but to date, there is no one definite answer.

Some scientists argue that length of life is related to the DIET of the animal. Herbivores live longer than carnivores. Some common European herbivores including bison and red deer can live to about 40 years, whereas our carnivores tend to live much shorter lives. But there are too many exceptions to this rule for it to be accepted.

On closer examination, maybe it's not WHAT the animal eats, but the SIZE of the animal that dictates how long they will live. Herbivores tend to be larger in size than carnivores. Big is beautiful in the animal kingdom. The bigger you are, surely, the better protected you are against predators. Yes, this seems plausible, but again, there are too many exceptions for it to be totally accepted.

It’s not just WHAT we eat or how BIG animals are, that decide how long they live for. Another theory states that animals are pre-programmed to live to a certain number of HEARTBEATS and when they reach this number, they die. The most commonly held figure is one billion.

In the 1930’s the scientist Max Kleiber developed his famous law, Kleiber’s Law, which states that the metabolic rate of an animal is proportional to the mass of the animal. It appears that there is also a relationship between how fast a mammal’s heartbeats and how long it lives for. The number of heartbeats per lifetime tends to be stable or constant from species to species, for example, hamsters live for about 3 years whereas Arctic whales live for about 150 years, but they both have about one billion heartbeats. Bigger animals just take longer to use up their quota!

In fact, there is a formula that can predict how long a mammal will live for:

a = 1902.6 / h where a = mammal’s lifespan andh = heartbeat

Using the above formula we can calculate the lifespan of a Shrew or an Elephant.

SHREW: heartbeat=800 per minute. a= 1902.6 / 800 = 2.38 years.

ELEPHANT: heartbeat= 25 per minute. a= 1902.6 / 25 = 76.1 years.

This formula works fine for mammals living in the wild, giving answers such as 3 years for a hamster and 150 years for Arctic whales. It also works well for rats and mice and rabbits to mention just a few common mammals.

But what about humans? If we use the above formula with an average of 70 heartbeats per minute we get a lifespan of a little over 27 years. But we humans live a lot longer than this! What’s gone wrong? Nothing really. Before civilization, the average lifetime was about 30 years and primitive cultures that exist today with little or no contact with the outside world have an average lifespan of about 30 – 40 years. Nowadays, we humans have no natural predators, a plentiful diet and have access to many medicines, in particular, antibiotics and vaccines and there are vast improvements in sanitation. People live longer now because we are better equipped to deal with infection and our living conditions have improved considerably. The number of heartbeats has risen from one billion up to three billion, giving us a lifespan of approx. 80 – 85 years.

But what about your genes? Surely, these must have some input into how long we live for. Dr. Cynthia Kenyon from the University of California, has found a gene in worms, that when it is altered, will cause the animal to age more slowly. She has managed to more than double the lifespan of these worms from one month to more than two months when she succeeded in causing a mutation to the (daf-2) gene. Humans who live to 90 or 100 have more mutations in a similar daf-2 gene in their bodies. She predicts that within 15 years, youth boosting drugs will be on the market.

But what can I do in the meantime? If I could somehow s-l-o-w down my heartbeat. Maybe I should try yoga or meditation.

I’ve just got to remember: Live Fast-Die Young