However, I don't suppose any of us wants long life at the cost of being a tree. Trees live long, but they live slowly, passively, and in terribly, terribly dull fashion. Let's see what we can do with animals.

Very simple animals do surprisingly well and there are reports of sea-anemones, corals, and such-like creatures passing the half-century mark, and even some tales (not very reliable) of centenarians among them. Among more elaborate 'invertebrates, lobsters may reach an age of 50 and clams one of 30. But I think we can pass invertebrates, too. There is no reliable tale of a complex invertebrate liv ing to be 100 and even if giant squids, let us say, did so, we don't want to be giant squids.

What about vertebrates? Here we have legends, par ticularly about fish. Some tell us that fish never grow old but live and grow forever, not dying till they are killed. In dividual fish are reported with ages of several centuries.

Unfortunately, none of this can be confirmed. The oldest age reported for a fish by a reputable observer is that of a lake sturgeon which is supposed to be well over a century old, going by a count of the rings on the spiny ray of its pectoral fin.

Among amphibia the record holder is the giant sala mander, which may reach an age of 50. Reptiles are better.

Snakes ma reach an aoe of 30 and crocodiles may attain y t,

60, but it is the turtles that hold the record for the animal kingdom. Even small turtles may reach the century mark, and at least one larger turtle is known, with reasonable certainty, to have lived 152 years. It may be that the large Galapagos turtles can attain an age of 200.

But then turtles live slowly and dully, too. Not as slowly as plants, but too slowly for us. In fact, there are only two classes of living creatures that live intensely and at peak level at all times, thanks to their warm blood, and these are the birds and the mammals. (Some mammals cheat a little and hibernate through the winter and probably ex tend their life span in that nianner.) We might envv a tiger or an eagle if they. lived a long, long time and even

— as the shades of old age closed in-wish we could trade places with them. But do they live a long, long time?

Of the two classes, birds on the whole do rather better than mammals as far as maximum age is concerned. A pigeon can live as long as a lion and a herring gull as long as a hippopotamus. In fact, we have long-life legends about some birds, such as parrots and swans, which are supposed to pass the century mark with ease.

Any devotee of the Dr. Dolittle stories (weren't you?) must remember Polynesia, the parrot, who was in her third century. Then there is Tennyson's poem Tithonus, about that mythical character who was granted immortality but, through an oversight, not freed from the incubus of old age so that he grew older and older and was finally, out of pity, turned into a grasshopper. Tennyson has him lament that death comes to all but him. He begins by pointing out that men and the plants of the field die, and his fourth line is an early climax, going, "And after many a summer dies the swan." In 1939, Aldous Huxley used the line as a title for a book that dealt with the striving for physical im mortalit y

However, as usual, these stories remain stories. The oldest confirmed age reached by a parrot is 73, and I imagine that swans do not do much better. An age of 115 has been reported for carrion crows and for some vultures, but this is with a pronounced question mark.

Mammals interest us most, naturally, since we are mam mals, so let me list the maximum ages for some mammalian types. (I realize, of course, that the word "rat" or "deer" covers dozens of species, each with its own aging pattern, but I can't help that. Let's say the typical rat or the typical deer.)

Elephant 77 Cat 20

Whale 60 pig 20

Hippopotamus 49 Dog 1 8

Donkey 46 Goat 17

Gorilla 45 Sheep 16

Horse 40 Kangaroo 16

Chimpanzee 39 Bat 15

Zebra 38 Rabbit 15

Lion 35 Squirrel 15

Bear 34 Fox 14

Cow 30 Guinea Pig 7

Monkey 29 Rat 4

Deer 25 Mouse i

Seal 25 Shrew 2

The maximum age, be it remembered, is reached only by exceptional individuals. While an occasional rabbit may make 15, for instance, the average rabbit would die of old age before it was 10 and might have an actual life ex pectancy of only 2 or 3 years.

In general, among all groups of organisms sharing a common plan of structure, the large ones live longer than the small. Among plants, the giant sequoia tree lives longer than the daisy. Among animals, the giant sturgeon lives longer than the herring, the giant salamander lives longer. than the frog, the giant alligator lives longer than the lizard, the vulture lives longer than the sparrow, and the elephant lives longer than the shrew.

Indeed, in mammals particularly, there seems to be a strong correlation between longevity and size. There are exceptions, to be sure-some startling ones. For instance, whales are extraordinarily short-lived for their size. The age of 60 1 have given is quite exceptional. Most cetaceans are doing very well indeed if they reach 30. This may be because life in the water, with the continuous loss of beat and the never-ending necessity of swimming, shortens life.

But much more astonishing is the fact that man has a longer life than any other mammal-much longer than the elephant or even than the closely allied gorilla. When a human centenarian dies, of all the animals in the world alive on the day that he was born, the only ones that re main alive on the day of his death (as far as we know) are a few sluggish turtles, an occasional ancient vulture or sturgeon, and a number of other human centenarians. Not one non-human mammal that came into this world with him has remained. All, without exception (as far as we know), are dead.

If you think this is remarkable, wait! It is more re markable than you suspect.

The smaller the mammal, the faster the rate of its metabolism; the more rapidly, so to speak, it lives. We might well suppose that while a small mammal doesn't live as long as a large one, it lives more rapidly and more intensely. In some subjective manner, the small mammal might be viewed as living just as long in terms of sensation as does the more sluggish large mammal. As concrete evidence of this difference in metabolism among mammals, consider the heartbeat rate. The following table lists some rough figures for the average number of heartbeats per minute in different types of mammal.

Shrew 1000 Sheep 75

Mouse 550 Man 72

Rat 430 Cow 60

Rabbit 150 Lion 45

Cat 130 Horse 38

Dog 95 Elephant 30

Pig 75 Whale 17

For the fourteen types of animals listed we have the heartbeat rate (approximate) and the maximum age (ap proximate), and by appropriate multiplications, we can determine the maximum age of each type of creature, not in years but in total heartbeats. The result follows:

Shrew 1,050,000,000

Mouse 950,000,000

Rat 900,000,000

Rabbit 1,150,000,000

Cat 1,350,000,000

Dog 900,000,000

Pig 800,000,000

Sheep 600,000,000

Lion 830,000,000

Horse 800,000,000

Cow 950,000,000

Elephant 1,200,000,000

Whale 630,000,000

Allowing for the approximate nature of all my figures,

I look at this final table through squinting eyes from a dis tance and come to the following conclusion: A mammal can, at best, live for about a billion heartbeats and when those are done, it is done.

But you'll notice that I have left man out of the table.

That's because I want to treat him separately. He lives at the proper speed for his size. His heartbeat rate is about that of other animals, of similar weight. It is faster than the heartbeat of larger animals, slower than the heartbeat of smaller animals. Yet his maximum age is 115 years, and that means his maximum number of heartbeats is about 4,350,000,000.

An occasional man can live for over 4 billion heartbeats!

In fact, the life expectancy of the American male these days is 2.5 billion heartbeats. Any man- who passes the quarter-century mark has gone beyond the billionth heart beat mark and is still young, with the prime of life ahead.

Why? It is not just that we live longer than other mam mals. Measured in heartbeats, we live four times as long!

Why??

Upon what meat doth this, our species, feed, that we are grown so great? Not even our closest non-buman rela tives match us in this. If we assume the chimpanzee to have our heartbeat rate and the gorilla to have a slightly slower one, each lives for a maximum of about 1.5 billion heartbeats, which isn't very much out of line for mammals generally. How then do we make it to 4 billion?

What secret in our hearts makes those organs work so much better and last so much longer than any other mam malian heart in existence? Why does the moving finger write so slowly for us, and for us only?

Frankly, I don't know, but whatever the answer, I am comforted. If I were a member of any other mamxnalian species my heart would be stilled long years since, for it has gone well past its billionth beat. (Well, a little past.)

But since I am Homo sapiens, my wonderful heart beats even yet with all its old fire; and speeds up in proper fashion at all times when it should speed up, with a verve and efficiency that I find completely satisfying.

Why, when I stop to think of it, I am a young fellow, a child, an infant prodigy. I am a, member of the most un usual species on earth, in longevity as well as brain power, and I laugh at birthdays.

(Let's see now. How many years to 115?)