In 1513, Ponce de Leon searched Florida in vain for the fabled fountain of youth. No one blames him for his exhaustive and futile search. It is an accepted fact that old people or more likely than younger people. One in every 20 men will die before his 71st birthday. The risk we run of dying at any age is scientifically called the "force of mortality".



The force of mortality is a figure that has been worked out for all ages of people and it grows greater with older age. This is the number at which life insurance rates are based on. If you went through life today with the same force of mortality that we had at five years old, never becoming any likelier to die than we were then, we could all hope to live to a hundred years unless we were careless or really unlucky. But the fact that we do not live several hundred years and only rarely reach 100 is because of a process called "aging".

Aging in human beings is recognized by the graying and thinning hair, weakening of muscles, wrinkling of skin, loss of hearing and other physical shrinking. Aging also reduces our powers of staying well. There just comes a time when it becomes very difficult to stay alive and so we die. This is the end of our life span.

Man and other animals that age have fixed lifespans or characteristic ages of death. While some might live longer than others, most individuals of the species have about the same line of life. For humans, a common length of life is between 75 to 80 years old, provided that they are nurse to get food and medical care. If there is hunger or little medical care, humans most likely die young and sometimes do not survive infancy. Women, on the other hand, nearly always outlive men. People who come from long-lived families also live longer than others. Most animals are similar to humans in having fixed lifespans. As a general rule, the larger species of any group live longer than the smaller ones. Tortoises and sturgeon are probably the two longest-lived vertebrates. Man holds the distinction for being the longest lived mammal. The elephant is the only other mammal that approaches our life span.

We are so used to the idea of ourselves getting older that we would be surprised to know that there are animals that do not age. An example would be sea anemones. Some anemones have been kept for more than a century without showing any signs of losing vitality. Some marine worms can even grow backwards; if they are not fed or are kept in the dark, they get smaller until they become a ball of cells. It has also been sad that small wild animals and some birds do not age, but what really happens is that they do not have a chance to age. Nearly all of them die by accident before they get the chance to grow really old. A few small birds in the wild can survive for more than a couple of years but if they are placed in a cage, protected from enemies and hunger, they can live as long as 20 years, but they will also die of old age.

In summary, an animal that does not age is not immortal. It is not deathless. These individual species do die from disease or from accidents. These animals are just not threatened with death from old age. The force of mortality stays the same in them.