Today, grow old with me. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

Aging is, without doubt, a great mystery of the human condition. We all watch ourselves age with mixed feelings. Sometimes we watch with horror, sometimes with resignation. Sometimes the luckier among us age with a peculiar sense of fulfillment.

Not all living things age. Queen bees don't age. The worker bees simply kill them when they stop being fertile. Rockfish and some pine trees don't age. They last until the erratic forces of nature kill them. If we didn't age, those forces would catch up with half of us by the age of about 600 years. That seems like rather more life than any of us would really want.

In other species, old age arrives all at once. At a point in the life of the Pacific salmon, his body releases a rush of hormones called glutocorticoids. They put a stop to normal body maintenance functions. A healthy Pacific salmon dies of old age very suddenly.

Human aging is far less systematic than that. Our systems shut down in different ways and at different rates. One person becomes cancer prone. Muscle tone deteriorates in another. One 70-year-old is still youthful. Another is old, old, old.

Some aging diseases result from processes that help us earlier in life. Sickle cell anemia infects so many Africans because, in the short term, sickle cells protect them from malaria. Huntington's disease attacks us in old age. But it seems to assure its own survival by increasing its victims' sex drive when they're younger.

The surest and simplest means for delaying old age is to eat less. If we cut our calorie intake by 30 percent, we live longer. Unless we're very thin, we're most under the assault of aging when we're overweight.

The reason for that isn't very dramatic. Most foods pump a lot of junk into our system. If we eat less, we simply accrue less poison.

Yet, in the end, I wonder if we'd really want to end our life like the rockfish -- in the full flush of youth. I like what Shakespeare said about aging:

Fear no more the heat o' the sun,
Nor the furious winter's rages;
Thou thy worldly task hast done,
Home thou art and ta'en thy wages.
Golden lads and girls all must,
As chimney-sweepers, come to dust.

Shakespeare says the reward of aging is accrued accomplishment. It's the knowledge that our mind has served us all. And that, of course, is a legacy we can still add to -- even when we no longer run the 440 in less than a minute.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)

Sapolsky, R.M. and Finch, C.F., On Growing Old. The Sciences, March/April 1991, pp. 30-38.