There are
numerous ways to apply evolutionary biology to our needs today, among them:
1.
prolonging the
life of drug/chemical resistant compounds
2.
constructing
evolutionary trees
3.
pathogen
tracking
4.
industrial
production of biochemicals and other agents
1. Drug resistance and chemical resistance in microbes, plants,
and animals. In the latter
half of this century, industry has been exceptionally good at providing
compounds to kill viruses, bacteria, insects that eat crops and weeds that grow
in crop fields. We even have an abundance of chemotherapy drugs to kill rogue
cancer cells. Yet virtually without exception, our attempts to kill these
organisms cause them to evolve resistance against the chemicals used to kill
them. For example:
AIDS is an example of a virus that
evolves to thwart its destruction.
·
Isolates of the AIDS virus with up to 15 different drug-resistance
mutations are known, and the latest drugs are becoming ineffective.
·
Some strains of bacteria are resistant to all available
antibiotics.
·
For multi-drug resistant tuberculosis, surgery is the only cure
because antibiotics don’t work and only 50% of those infected survive.
·
Chemotherapy for cancer often fails because drug-resistant cells
evolve during treatment.
·
Pesticide resistance and herbicide resistance is so common now
that the financial incentive to make new pesticides and herbicides is
break-even or worse.
Evolutionary biology suggests how best to prolong the useful life
of drugs/chemicals. The amounts of chemicals used, what combinations of
chemicals to use, and when to apply them are all questions that can be assessed
from the perspective of preventing or slowing the evolution of resistance. In
some cases now, the companies marketing the compounds have a financial interest
in maintaining the longevity of their product, and they are funding studies by
evolutionary biologists to develop wise use protocols. In other cases, however,
economic and emotional forces dictate policies that speed up the evolution of
resistance (e.g., patients demand and physicians write prescriptions for
antibiotics for viral infections; antibiotics are used in animal feed).
Evolutionary trees help scientists
track pathogens that cause disease.
2. Evolutionary trees Perhaps the core of evolutionary theory is that all life forms are
connected to each other through common ancestry. Molecular biology has
reinforced this view to a far greater level than was deemed possible even 50
years ago. On a short time scale, of course, we observe that this is true —
everything alive comes from something else that is both alive and similar. One
of the big developments in evolutionary biology over the last 2 decades is a
methodology to estimate the underlying patterns of ancestry among living
things. These reconstructions of evolutionary history are known as phylogenies,
or phylogenetic trees, because they are branched somewhat like trees when drawn
from bottom to top. We can use molecular data to estimate the common ancestries
of life as far back as we like — for example, between bacteria and our
mitochondria (the energy-producing organelles in our cells). But we can also
use these methods to estimate much more recent ancestries. And these methods
have found many worthy uses in tracking infectious diseases.
3. Molecular epidemiology — pathogen tracking To an epidemiologist studying infectious diseases, it is very
useful to know how or where a person became infected with the disease. This
information is perhaps the most basic fact we can use in preventing the further
spread of a disease. For over a decade now, epidemiologists have been using DNA
sequences of viruses to make phylogenetic trees and thereby track the sources
of infections. Some of these examples are spectacular.
Law: A case of
intentional HIV injection?
In a highly publicized case in Lafayette, Louisiana in 1998, a woman claimed that her ex-lover (a physician) deliberately injected her with HIV-tainted blood (HIV is the virus that causes AIDS). There were no records of her injection and no witnesses. So how could her story be tested? Evolutionary trees provide the best scientific evidence in a case like this.
In a highly publicized case in Lafayette, Louisiana in 1998, a woman claimed that her ex-lover (a physician) deliberately injected her with HIV-tainted blood (HIV is the virus that causes AIDS). There were no records of her injection and no witnesses. So how could her story be tested? Evolutionary trees provide the best scientific evidence in a case like this.
A woman’s claim to how she was
infected with AIDS was supported by evolution.
·
HIV picks up mutations very fast — even within a single
individual.
·
If one person gives the virus to another, there are few
differences between the virus in the donor and the virus in the recipient.
·
As the virus goes from person to person, it keeps changing and
gets more and more different over time.
·
Thus, the HIV sequences in two individuals who got the virus from
two different people will be very different.
·
Thus, if the woman’s story were true, her virus should be very
similar to the virus in the person whose blood was drawn but should be very
different from viruses taken from other people in Lafayette.
·
That was exactly what the evolutionary trees showed; her virus
appeared to have come from the patient’s virus but was unlike the virus taken
from other people in town.
·
Since there was no way to explain how she would have gotten that
patient’s virus on her own, the evolutionary analysis supported her story.
(Incidentally, this case was the first use of phylogenetics in U.S. criminal
court.)
Other cases Evolutionary trees have been used in many other cases of
infectious disease transmission:
· the transmission of the AIDS virus by a dentist to his patients
· deer mice as the source of hantavirus infections in the
Four-Corners area
· the source of rabies viruses in human cases, leading to the
discovery of a case in which rabies virus took at least 7 years to kill a
person
· whether recent cases of polio in North America were relict strains
from the New World, were vaccine strains, or were introduced from Asia
4. Industrial production of biochemicals and other agents “Directed evolution”, i.e. artificially-induced evolution, has
become part of the jargon in biotechnology:
Biotechnology allows us to give
direction to evolution.
· Artificially evolved enzymes and other proteins are soon to become
part of household and medical technologies.
· We will have protein-based drugs that, unlike the proteins inside
our bodies, degrade slowly so that we don’t need to take so much of them.
· Enzymes are being evolved to work in detergents (which they don’t
normally do).
· And as the stuff of futuristic novels, molecules are being
developed to bind anthrax spores, ricin molecules, and other potential
bioterrorism agents.
All of these developments take advantage of one or more forms of
test-tube evolution. Armed with a knowledge of how natural selection works and
combined with the right kinds of laboratory technology, people can create
molecules to perform seemingly any kind of function. In some of the more
spectacular cases, these test tube evolution methods have created enzymes from
purely random pools of DNA (or RNA) sequences. Even 10 years ago, it was
thought that a DNA enzyme was impossible, yet armed with only an understanding
of how to apply test tube evolution, a DNA enzyme can now be created in days.
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