Health policy: Human disease cannot be eradicated

M. David Drapeau

One of today’s most serious and pressing issues is health care. People generally desire to live longer and stronger, and they are – in large part because of excellent medical care. Doctors and medical scientists collaborating with pharmaceutical companies are alleviating the effects of many diseases, allowing ill people to live more comfortably. In some cases there has been success in proactive prevention. This is wonderful, and is a testament to incredible progress in science, technology, and medicine during the last century.

Medical professionals, aided by the media, often state that they are working towards the noble goal of eradicating disease. A commonly heard phrase is that scientists are “curing cancer.” While people’s hearts and dreams are in the right place, this is a misnomer. In the broadest sense, modern medicine will never cure all disease, or even most disease.

This is why.

One of the profound biological discoveries from the last half century was that genes and their protein products can, and often do, have age-dependent effects. In other words, a gene might be crucial for early development (perhaps in the embryo), be silent during childhood, and then play a later role during puberty and adulthood. This is true not only in humans but in all animals.

A necessary consequence of this type of gene action is that some genes will have effects in very late life. The term “late-life” is defined as being post-breeding-age.

Gerontologists and evolutionary biologists have defined two related ways by which harmful gene action occurs in late-life.

The first is called “antagonistic pleiotropy,” a fancy term describing when a gene has multiple functions, some of which are beneficial in earlier life, and some of which are deleterious in late-life. In this situation, a gene will tend to stay in a population of individuals, because of its important early beneficial effects. The deleterious effects cannot be detected by natural selection, because they occur only after the gene has already been passed on to offspring. (As an example, the gene reveals its damaging effects when a person is 60, but by that time the maladaptive gene has already been passed on to that 60 year old’s two children, aged 38 and 32…Indeed, the gene may have already been passed on to 10 year old grandchildren.)

The second mechanism, “mutation accumulation,” is similar and involves a mutation in a gene that has no net positive or negative beneficial effects, yet yields harmful effects in late-life. This kind of gene will accumulate in genomes because natural selection cannot weed it out, since, again, harmful effects occur after the gene has already been bred into the next generation of individuals. Natural selection cannot “see” the harmful effects of the gene. (This is effectively why natural selection cannot select against death, and why all higher organisms senesce.)

Deleterious gene effects are the essence of inherited disease. Diseases and disorders will always exist. This is not mere pessimism, because even if we were to assume an extreme hypothetical case in which medical scientists cured every genetic disease that acts up to, say, 120 years of age, there will always exist genes that exert a harmful effects after age 120. Such a gene effect could not possibly be observed before humans commonly survive past the age at which it has a harmful effect on health.

Every day, medical professionals are uncovering mechanisms for preventing specific diseases from occurring, and discovering methods for dealing with such diseases once they’ve sprouted. These are obviously wonderful advances, and research leading to these outcomes should be pursued, and highly funded. For the average lifespan of humans to be extended to 100, or 120, or 150, particularly if these are “healthy years,” would be incredible for many reasons.

However, in the most general sense, doctors will never eradicate disease, and the media does the public a disservice when they imply that they someday will. Modern medicine and media, along with the general public, would benefit greatly from consideration of underlying biology when discussing disease.


Further reading:

Rose, M.R. (1991). Evolutionary Biology of Aging. Oxford University Press.

Rose, M.R. (2005). The Long Tomorrow: How Advances in Evolutionary Biology Can Help Us Postpone Aging. Oxford University Press.

Special Report: Curing Cancer. (1998). Time Vol. 151 No. 19 (May 18, 1998).

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The author is currently a scientist in New York, NY and has a B.S. and Ph.D. in biology.

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