The proponents of intelligent design and other organized opponents of evolutionary
biology do not dispute the overwhelming evidence that microbes can evolve rapidly,
over the course of months or even days. Instead, most skeptics focus their criticism
on larger-scale evolutionary patterns, particularly the common ancestry of all
living things and the generation of complexity through natural selection. So
why is teaching microbial evolution critical for the public to understand evolution
on both the small and large scales?
One word immediately comes to mind: disease. Disease evolution is of immense
practical concern, and it happens fast. Even though the critics of evolutionary
biology rarely dispute these examples of microbial evolution on human timescales,
the public appears largely unaware of the importance and success of evolutionary
biology in dealing with human disease.
Microbial pathogens have huge populations, undergo rapid generation times, experience
high mutation rates and often face strong selection pressures — the perfect
combination for rapid evolutionary change. Evolutionary biology directly helps
us understand the rapid evolution of microbial pathogens.
Many emerging infectious diseases enter the human population from animal sources
and then evolve the ability to be transmitted from human to human. We saw this
recently and dramatically with the SARS coronavirus and we fear a similar progression
with H5N1 avian influenza (so-called bird flu). Evolutionary models illuminate
the processes by which diseases evolve to shift from animal hosts to humans
and suggest ways of reducing the chance of that occurring.
Other microbial pathogens rapidly evolve resistance to the drugs that we use
to treat them, creating enormous problems for society. Experimental evolution
studies, in which bacterial populations evolve in real time in a laboratory
setting, have uncovered the pathways by which bacteria develop antibiotic resistance,
and thus suggest ways to counter drug resistance. Mathematical models help us
predict the spread of resistant strains among hospitals, communities and farms
where antibiotics are used heavily as growth supplements; furthermore, they
suggest ways that we can alter our pattern and practice of antibiotic use so
as to minimize subsequent evolution and the spread of drug resistance.
In yet another example, the human immunodeficiency virus (HIV) evolves so fast
that the course of treating an individual with HIV is literally an exercise
in applied evolution. The selection and timing of anti-retroviral drugs are
chosen to best prevent, or at least compensate for, this virus’ rapid ability
to evolve drug resistance.
Evolutionary biology also helps us reconstruct the history of microbial transmission
and evolution, which can help scientists figure out how to treat microbial pathogens.
When choosing which strains to include in each year’s influenza vaccine,
for example, researchers consider the evolutionary histories of the currently
circulating strains of the virus. Similarly, models of tuberculosis strains
in San Francisco have helped researchers work out the origins of infection and
the patterns of transmission in crowded urban environments, thereby guiding
efforts for control and prevention.
Such examples make it clear what evolutionary biology is, what it is not, and
what it can do for us. In particular, teaching about microbial evolution provides
a way to engage and counter two common public misconceptions about the nature
of evolutionary biology, both of which stem from the mistaken premise that evolutionary
biology is limited to the study of how things came to be, over very long periods
of time.
The first misconception (or deliberate sophistry, in some cases) goes roughly
as follows: Evolutionary biology deals exclusively with processes that occur
only on geological timescales. Therefore we cannot do manipulative experiments
in the study of evolution, and consequently evolutionary theory is not testable.
Thus evolutionary biology is an ideology, not a testable scientific theory.
Of course, it is simply false that a theory cannot be tested without conducting
manipulative experiments. We can always test a theory proposed at one point
in time by looking to data that become available at some subsequent time —
or even by looking at the currently available data in a new way. Much of the
scientific research in cosmology, for example, proceeds by this approach.
Still, this misconception remains a sticking point in public thought, and it
is commonly exploited by opponents of evolution. By teaching about microbial
examples where manipulative experiments are entirely possible and commonly performed,
evolutionary biologists and others can illustrate that evolution is subject
to manipulative experiments and head off this false criticism before it can
be raised.
A second misconception is that religion and evolution are incompatible. In an
October 2005 CBS News poll, 29 percent of Americans stated that it is impossible
to believe in both God and evolution. The rationale goes something like this:
Evolutionary biology is a way of answering the question “How did we
come to exist and how did our world come to be the way that it is?” Therefore,
evolution is a set of beliefs about the world — a metaphysics — and
it happens to be a metaphysics that is incompatible with religious doctrine.
Therefore, one must choose between evolution and religion.
Every step of this logic chain is wrong. Evolution is a material process of
change; to access this process scientifically, we use materialist methods. Using
materialist methods does not commit us to any metaphysical perspective. In other
words, evolutionary biology is just a tool for doing a task — in this case,
the task of generating testable hypotheses based on material phenomena to help
prevent and treat infectious diseases. As it is just a tool, evolutionary biology
is no more incompatible with religion than is a screwdriver!
The basic ideas underlying evolutionary biology are well-illustrated by examples
from infectious diseases. Although these examples are rarely seen on the frontlines
of the “evolution wars,” they serve as a marvelous opportunity to
educate the public about what evolution is and even about what science is. In
our experience, students who have learned to understand evolution by exploring
this process at the level of microbial pathogens are much more savvy when it
comes to evaluating the evidence and arguments surrounding the topics of common
descent and emergent complexity.
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