Last week, a great deal of media hype centered on the discovery of a so-called immortality gene by a research team at the Baylor College of Medicine. In the normal scheme of things human cells eventually stop dividing as they age, reach a quiescent stage called senescence, and die. By comparison, cancer cells can keep reproducing essentially forever and are often termed immortal.
A classic example is a sample of cervical cancer cells, code-named HeLa after the donor, received in a lab at Johns Hopkins University in 1951. In the years following, HeLa cells have contaminated cell cultures in research labs throughout the world. The Baylor group has identified a gene called MORF4 that appears to be involved in the conversion of a normal cell into a cancerous one. The researchers hope that the gene’s identification will help reveal how cancerous cells age and die. But the discovery is not going to help extend the human life span any time soon as some television reports might lead you to believe.
Coincidentally, a report on human longevity in the latest issue of American Scientist does give some insight into why life spans differ greatly among species and why some people live longer than others. The article, whose lead author is S. Jay Olshansky of the University of Chicago’s Department of Medicine and Center on Aging, says that the evolutionary goal is for individual members of a species to survive to maturity and reproduce. With the gene pool thus guaranteed, further survival of the individual serves no evolutionary benefit and may actually be detrimental to the species. This holds true for all species except our own and evolutionary biologists say that the growing problems linked to human senescence is a consequence of survival extending well into the post-reproductive period.
The article makes an analogy between the engineering of an Indy 500 race car and the life span of humans. The goal is to engineer a car so that all of its components will operate for at least another 500 miles. Failure beyond that goal is not important to either the engineers or mechanics because the car is not designed to operate after the end of the race. The situation would be greatly different if the race were run until every car fails. Some would break down early in the race, a few would last far beyond the expected life span of their parts, while the majority would fall somewhere between these two extremes. That all would break down eventually is inevitable as moving parts wore out with individual operating spans arising from the breakdown of parts due to engineering differences. The impossible task of engineering an immortal car is not considered as there is no race that requires it.
For humans the engineer is natural selection, the winner’s flag successful reproduction, and the race one of time rather than distance. Again a combination of genetic differences and environmental factors will decree that some will die early in life, a few live well beyond the normal life span, and the majority will fall somewhere in between. Normally the genetic differences are characteristic of the species and essentially a constant factor while the environmental factors can vary between individuals. Two related persons may have the same intrinsic life span but an added environmental factor, such as heavy smoking, can drastically alter one’s longevity over the other.
The intrinsic life span of humans, once thought to be unchangeable, has been altered in recent times due to successes in combatting diseases of both childhood and old age. As a result, children who would have died young now live to reproductive age and adults are increasingly living well beyond the normal human life span. But, just as an old car with many weak or defective parts can be kept on the road by a mechanic’s skills, medical advances in prolonging life are bringing to the forefront diseases that were not a problem in the past because too few people lived long enough to have them. As a result, say the authors, problems such as prostate cancer, Alzheimer’s disease, and osteoarthritis, and cancer will increasingly be part of the human condition.
Clair Wood is the Bangor Daily News science columnist.