This is the 2007 version. Click here for the 2017 chapter 10 table of contents.

What Causes Aging?

What causes aging? Several different theories have been suggested, and there could be a combination of several processes. The dominant theories involve programmed cell death, changes in nerve regeneration, and accumulation of genetic errors.

Aging as a programmed process

What is evidence that cell death is "programmed" into the body?

Some researchers believe that aging and even death are programmed into cells as a natural sequence of stages in development. Researchers have identified a single gene in fruit flies, dubbed reaper, which "appears to play a central control function for the initiation of programmed cell death" (White and colleagues, 1994). Cell death is necessary in normal developmental processes-for example, in the development of the nervous system. Could aging and death be a genetically controlled process in humans? We might age and die as a natural developmental sequence, not merely because of accumulated injuries or cell damage.

What is the progeroid syndrome?

A medical disorder in which the aging process appears to be accelerated is known as progeria or the progeroid syndrome or premature aging syndrome Progeria sufferers show signs of old age while still in childhood. Victims of progeria typically grow old before the age of 10, losing their hair, wrinkling, and dying before reaching their teen years.

How many genes are involved in triggering progeroid syndrome? What does this suggest?

Genetic studies show that premature aging syndrome involves a defect in only one gene. The fact that a single genetic defect can trigger rapid development and aging suggests that genetic control system regulates the aging process. People with progeria do not suffer from random DNA changes or degradation; they go through rapid hormonal development first, as if the entire developmental sequence is accelerated.

Accelerated aging can also be produced by hormonal imbalance, as shown by the case of Clarence Kehr. This illustration is from a 1931 article in American Psychologist titled, "A clinical study of 'Toledo's Strong Boy'" (McClure & Goldberg, 1931). It reports "the strange case of Clarence Kehr, Jr., who skipped from the cradle to adolescence in physical development." Clarence, shown at age 6, is in the middle of the photograph, with his brother and sister on either side.

"Toledo's Strong Boy" (from McClure & Goldberg, 1931)

Clarence's development was radically accelerated. He was able to lift his mother off the floor at the age of 5. He had prominent muscles, a mustache, and a baritone voice at age 6.

Clarence was proud of his weight-lifting abilities. He boasted of being the strongest boy in the world. He did not associate with other children, preferring "to do the same things that older people do." His mustache began to appear when he was 11 months old. By the age of 4, his sexual development was the same as a 14-year-old boy, and he was interested in girls.

X-ray studies revealed that Clarence, at age 6, had bone structure typical of a sixteen to eighteen year old. At the time the article was written, Clarence's parents were trying to work out a program of private instruction for him. Mentally, he was a normal 6 year old with average or below-average academic abilities. For example, he could not copy a diamond pattern, or verbally describe a picture, both standard items for 7-year-olds on the 1930 Stanford-Binet IQ test.

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