Dealing Darwinianly
with Illness
From a review of Why
We Get Sick: The New Science of Darwinian Medicine
by Randolph M. Nesse and George C. Williams (1995,
Human beings have
attempted to deal with the circumstances of their lives with the aid of such
guiding principles as pantheism, monotheism, essentialism, capitalism, geocentrism and a host of others. But the ism of
The authors
demonstrate the benefits of the evolutionary approach to both medical practice
and research through illustrations drawn from a wide variety of medical issues
organized in six categories of explanation: (1) processes by which the human
organism defends itself, (2) the dynamics of infection, (3) altered
environments, (4) inherited traits, (5) constraints on design imposed by
initial conditions, and (6) disorders brought into existence by events in
adaptation history.
Why We get Sick reveals a panorama of the
battles fought daily within our bodies. Although selected illustrations vary in
empirical verification -- some are almost entirely speculative, others are
well-substantiated by research findings --, in sum, they reveal a broad
spectrum of possible ways in which evolutionary thinking accelerates progress
toward effective handling of medical problems.
Disclaimers in the
preface warn that while the book is aimed at showing how consideration of
ultimate causes can and should change approaches to medical issues,
it does not propose yet another "alternative" medicine. It does urge
that patients, doctors, and researchers alter their thinking and their
procedures to bring medical practices into line with what is already known and
what can further be known through the evolutionary perspective.
Mechanisms of
defense include pain, fever, inflammation, and expulsions (coughs, sneezes,
diarrhea, etc.). While uncomfortable for the patient, these are best considered
protective devices rather than disorders in themselves. The habits of earlier
generations in which doctors hesitated to "treat symptoms" and would
often "let nature take its course," are supported by recent studies.
For example, administering iron supplements have been found to delay recovery
from infectious disease because the reduction of iron in the blood which
accompanies infection aids recovery by depriving bacteria of a scarce and vital
substance.
The enormous
increase in the average length of life over the last two centuries is largely
attributable not to medical advances, but to improved diet and to public works
based on scientific knowledge of the processes whereby contagion occurs and can
be stopped. Bacteria and viruses are sophisticated opponents in a continual
escalating competition in which pathogens evade host defenses via various
techniques. While we have evolved resistance to smallpox and TB in the last
dozen generations, when it comes to evolving new tactics, our opponents run
rings around us. Bacteria can evolve as much in a day as we can in 1000 years
and there are as many bacterial cells in each of our guts as there are people on earth. That even improbable mutations occur
with frequency in populations of pathogens gives them a decided advantage.
Although we counter by altering antibody ratios and catastrophic epidemics can
sometimes increase host resistance in months, mostly it's not us, but the
pathogens that change. As Nesse and Williams
emphasize, the end of the war is nowhere in sight. The 20th century was the
golden age of relief from infection, but it may be over and this may accurately
be considered a "post-antimicrobiol era."
Many preventable
diseases result from environmental changes. Our Stone Age tastes today cause
overeating of foods abundant now (notably fats and sweets), but scarce then and
needed in small quantities. We also evolved aversion to toxic substances, but
we lack built-in aversions to contemporary dangers that were missing in ancient
environments. For example, skin cancer, which has increased in recent years,
results from a pattern of irregular sun exposure characteristic of urban living.
Suntan is a defense. It is not heat that burns but a photochemical reaction
which can overstimulate the immune system. Sun
screens which block shorter ultraviolet rays (UV-B) but allow too much of the
longer waves (UV-A) may harm in the long run. Exposure to the sun's rays should
allow acquisition of a protective tan. Melanomas are a function not of time in
the sun but the number of severe burns. The reduction in protective melanin
evolved among those living in Northern climates. Today, people of darker skin
who live in cold climates are subject to rickets since dark skin is a defense
against over-exposure to sun. Pale skin, while subject to sunburn, allows more
rapid acquisition of vitamin D.
The allergic
reaction is a major mystery. For one thing, it is increasing. Hay fever was
unknown in
In some cases,
disease is a direct result of genes. But why would natural selection permit a
harmful gene to persist in the population? For some illnesses the same gene
that causes a specific disorder also produces an advantage. The best known
example is the protection against malaria conferred by the same gene that
causes sickle cell anemia among sub-Saraha Africans
in areas in which malaria is common. Other cases are genes that produce
benefits early in life and disease later. Huntington's disease,
is not manifest until the fifth decade after reproduction has already occurred.
Schizophrenia's worldwide uniform rate of 1% suggests an ancient beginning and
the likelihood that its genes confer an as yet unknown advantage. Could it be
creativity? Reports indicate high levels of accomplishment among relatives. Or
it might be that the gene for schizophrenia affords protection from some
disease as is the probably the case with cystic fibrosis and Tay-Sachs disease. When a disadvantage is genetically
attached to an advantage control is difficult. Even harder to control are
genetic "quirks," harmless under prior conditions or selected because
they bring benefits, but not beneficial under present conditions. Genes also
bring disease through harmful mutations and through outlaw genes that
facilitate their own transmission at the expense of the individual.
It is in the nature
of design by evolution that compromises are inevitable. Choking is the result
of a structure shared among vertebrates in which the mouth is below and in front
of the nose but the food-conveying esophagus is behind the air-conveying
trachea. As a result the tubes cross and if the reflex that seals the opening
fails causing food to block the intersection, air cannot get to the lungs. Thousands of people die yearly because of this evolutionary
"mistake." Other compromises came with the shift to bipedalism and increases in the size of the cranium.
The legacies of our
evolutionary past also include plantar fascitis (heel
spurs) which probably did not bother Stone Age people whose habits of walking
and squatting contrast with our many hours of sitting in chairs. Nor was
alcohol addiction a problem for people who had to make their own under
primitive conditions of scarce raw materials and primitive equipment.
Nesse and Williams note that
psychiatry has had no coherent theory of emotions. By aping quantitative
science and stressing proximate molecular processes, they focused on pathology
before understanding the normal functions of the mechanisms involved. The
authors advance the theory that emotions adjust cognition, physiology,
subjective experience and behavior so that the organism can respond effectively
to particular events.
Perhaps it is not
surprising that medicine is late in addressing evolutionary questions. In the
traditional view, the question of why something maladaptive has been shaped by
evolution is contradictory. Furthermore, there exists a persistent antipathy to
evolutionary ideas in general and to natural selection in particular even among
some biologists. Nesse and Williams launch strong
criticisms against present-day methods of medical training with over-crowded
curricula that fail to find room for addressing evolutionary questions of what
is there about the species makes it susceptible to particular disorders. The
same problem exists in medical research, not only on the part of scientists,
but also on the part of funding sources. Nesse and
Williams suggest that Darwinian medicine needs its own funding.
Darwinism places
responsibility squarely on our own collective shoulders. The ways of natural
selection are losing their mystery and with that we are losing faith that the
best we can do is comfort the sick, obey the mores of our group, obey our
natural instincts, and pray to unseen powers for deliverance. The authors of Why
We Get Sick: The New Science of Darwinian Medicine,
foresee a cultural revolution in which the search for external guidance while
holding ourselves sacred and inviolate, is replaced with awareness that
humanity must decide its own fate. The free lunch counter is permanently
closed.
In a sense, this is
a political document. It says to doctors and patients that they better look
out. With the best of intentions, they may be doing the wrong things. The
difference between the evolutionary perspective and the approach it would
supplement is not insignificant; it leads to conceptions that will upset the
favorite assumptions of the political Left as well as those of the Right.
The first step is to
understand the process of evolution. Only then can we effectively fight it. But
in recommending change based on Darwinism, these authors do not propose
eugenics. In the view of evolutionary scientists it is time to begin the
journey that will take us from being victims of our genes to being their masters.
From the gene's eye view, there is no reason why natural selection should be
concerned with the health, welfare, or happiness of the creatures it produces.
To know evolution is to try to counteract its fearsome methods and effects. We,
with our phenotypic wants, desires and ideologies, are separate from our genes.
What is good for them may not be so good for us. And what our genetic heritage
gives us as the apparatus with which we must work in wending our way through
the vicissitudes that constitute our life space, may often be good for neither
of us. Nowhere is this better illustrated than in medical practices and
theories. To know that we are sick, even to know how we are sick, may not lead
to knowing how to prevent or cure that sickness. In addition, we need to know
why we are sick for the suggestions such knowledge conveys about how to deal
with the sickness.
The headlines are
alarming. Diseases believed conquered are re-emerging. There are outbreaks of
Ebola in