Download Natural Selection Interview

December 2004
Natural Selection: How Evolution Works
Interview with Douglas Futuyma
ActionBioscience.org: What is natural selection, and how is it central
to the theory of evolution?
Futuyma: Natural selection is the process by which species adapt to their
environment. Natural selection leads to evolutionary change when individuals
Natural selection with certain characteristics have a greater survival or reproductive rate than
is how species
other individuals in a population and pass on these inheritable genetic
evolve by
characteristics to their offspring. Simply put, natural selection is a consistent
adapting to their difference in survival and reproduction between different genotypes, or even
environment.
different genes, in what we could call reproductive success. [A genotype is a
group of organisms sharing a specific genetic makeup.]
Natural selection The reason that natural selection is important is that it’s the central idea,
explains design stemming from Charles Darwin and Alfred Russel Wallace, that explains design
in nature.
in nature. It is the one process that is responsible for the evolution of
adaptations of organisms to their environment.
Darwin’s book On the Origin of Species by Means of Natural Selection caused
quite a stir when it appeared in 1859. Evidence to support evolution and
natural selection, of course, has accumulated over time, and now science
accepts that evolution is a fact and that natural selection explains very well
how adaptive evolution takes place.
ActionBioscience.org: Is natural selection the only mechanism of
evolution?
Evolution has
several
mechanisms.
Genetic drift
involves random
changes.
Futuyma: No, certainly not. There cannot be evolution without genetic
variation in the first place. So there must be mutation and often recombination
to generate the different genotypes or the different versions of the genes,
known as alleles, which then may or may not make a difference in the ability
of an organism to survive and reproduce. You can’t have any evolutionary
change whatever without mutation, and perhaps recombination, giving rise to
genetic variation. But once you have genetic variation, there are basically two
major possibilities:


Natural selection
is more
consistent,
adaptive change.
First, there is simply no difference between the different genotypes or
different genes in their impact on survival or reproduction, and in that
case, you can have random changes of one versus the other type in a
population or a species until eventually one replaces the other. That is
an evolutionary change. It happens entirely by chance, by random
fluctuations. That is what we call the process of genetic drift.
Genetic drift is very different from possibility number two, natural
selection, which is a much more consistent, predictable, dependable
change in the proportion of one gene vs. another, one genotype vs.
another. Why? Simply because there is some consistent superiority,
shall we way, of one genotype vs. another in some feature that affects
its survival or some feature affecting its reproductive capabilities.
Natural selection ActionBioscience.org: Does natural selection lead to new species, and
plays a role in
if so, how?
the origin of new
species.
Futuyma: It sometimes does but not always. A great deal of evolution by
natural selection can happen without the formation of new species. Natural
selection is only the process of adaptation within species, and we see many
examples of that. Under some circumstances natural selection does play a role
in the origin of new species, by which I mean a splitting of one species lineage
into two different lineages that do not interbreed with one another -- for
example, the splitting of one ancestral primate lineage into one that became
today’s chimpanzee and the other that became the hominid line resulting in
our own species. The process of splitting and becoming reproductively isolated,
that is, incapable of breeding with one another, can often involve natural
selection but perhaps not always.
ActionBioscience.org: Some take natural selection to mean survival of
the fittest. How does this slogan sometimes lead to misconceptions?
Futuyma: “Survival of the fittest” is a slogan that is really very misleading.
First of all, it’s not an adequate description of what really goes on in nature for
two reasons:

“Survival of the
fittest” is a
misleading term.

Sometimes there isn’t a “fittest” type. There may be several different
types that are equally fit for different reasons. Perhaps they’re adapted
to different facets of the environment. One is not going to replace the
other because each has its proper place in the environment.
Moreover, it’s not just a matter of survival. Natural selection is a
difference in reproductive success that involves both the ability to
survive until reproductive age and then the capacity to reproduce.
The notion of the survival of the fittest is also unfortunate because it has been
viewed as a kind of tautology, a kind of empty statement for those who say
that the fittest are those that survive and so there’s no real predictive content
to the notion of natural selection. That is simply false.
ActionBioscience.org: How do scientists interpret “chance,” and does
it play a role in natural selection?
Evolution
involves
unpredictable
chance.
Futuyma: Philosophers and scientists use “chance” only in the sense of
unpredictability. Chance means essentially that you cannot predict the
outcome of a particular event. For example, you cannot predict whether your
next child will be a son or a daughter, even though you can specify the
probability or likelihood. “Chance” does not mean lack of purpose or goal in
science. If it did, we could say that absolutely everything in the natural world
is by chance because we don’t see any purpose or goal in storms, in ocean
currents, or anything else. Evolution certainly does involve randomness; it
does involve unpredictable chance. For example, the origin of new genetic
variation by mutation is a process that involves a great deal of chance. Genetic
drift, the process I referred to earlier, is a matter of chance.
However, natural selection itself is the single process in evolution that is the
antithesis of chance. It is predictable. It says that, within a specific
Natural selection environmental context, one genotype will be better than another genotype in
provides
survival or reproduction for certain reasons having to do with the way its
predictability.
particular features relate to the environment or relate to other organisms
within the population. That provides predictability and consistency. So, if you
have different populations with the same opportunity for evolution, you would
get the same outcome.
ActionBioscience.org: Can natural selection select for future needs of a
species?
Futuyma: No, because natural selection is not like Mother Nature watching
Natural selection
over us. Since natural selection is totally an impersonal process that is nothing
cannot prepare
more than a difference, generation by generation, in the reproductive success
species for
of one genome over another, there’s no way that it can look forward to the
future needs.
future or guard against the possibility of extinction. What individuals have
right now that gives them superior adaptation may lead to disaster tomorrow.
ActionBioscience.org: Could you give us an example of natural
selection at work in the recent past?
The apple
maggot fly
evolved in
response to
change in
available food.
Futuyma: There are so many examples of that! One example is the apple
maggot fly. About 100 years ago it started to become a serious pest of apple
orchards in New England and New York State. It’s now a threat throughout
most of northern United States. It originally fed just on hawthorn fruits, but
then it adapted to apple and it’s become a serious threat to the industry. That
is a genetic change propagated by natural selection.
Perhaps much more crucial is an issue that agriculture has to deal with all the
time: the evolution in hundreds of species of insects of resistance to various
Resistance to
pesticides is due chemical insecticides. The insects then become more and more difficult to
control.
to adaptive
change.
Closer to home, and more serious, is the single greatest crisis in medicine:
antibiotic resistance. The fact is that enormous numbers of the most
Antibiotic
dangerous bacteria and viruses have evolved to be resistant to the antibiotics
resistance also
or other drugs that used to be effective against them. An obvious example is
illustrates
natural selection. the HIV virus, which, as we know, is capable of rapidly evolving resistance to
drugs that once were effective against it.
ActionBioscience.org: The late Stephen Jay Gould has written that if
we were to rewind the “tape” of evolutionary history and play it again,
the results would not be the same [S.J.Gould, Wonderful Life, 1989].
Why?
Futuyma: Well, it almost certainly would not be the same. I don’t think
anyone can say how different it would be, whether it would be along the same
general lines or utterly, unimaginably different.
Evolutionary
history could not
happen the same
way again.
Environmental
circumstances
cannot be
repeated.
Of course, it wouldn’t be the same, because first of all, random processes are
involved in the evolutionary process. For example, the origin of new
mutations: a lot of evolution is dependent on particular mutational changes in
genes that were very, very rare or unlikely, but that just happened at the right
time, in the right species, in the right environment, but it need not happen
that way. So, there’s this unpredictability.
In addition, the particular sequence of environmental changes that the Earth
underwent and that organisms were exposed to over billions of years has left a
long-term imprint on species as they are today. If the sequence of
environmental changes were different, you would have a different evolutionary
history, leading to entirely different organisms over time.
ActionBioscience.org: Why does natural selection pose a threat
philosophically to some people?
Futuyma: The philosopher Daniel Dennett called natural selection “Darwin’s
dangerous idea” for a good reason: it is a very simple natural mechanism that
explains the appearance of design in living things. Before Darwin, the
Natural selection
adaptations and exquisite complexity of organisms were ascribed to creation
makes the
by an omnipotent, beneficent designer, namely God, and indeed were among
“argument from
the major arguments for the existence of such a designer. Darwin’s (and
design”
Wallace’s) concept of natural selection made this “argument from design”
superfluous.
completely superfluous. It accomplished for biology what Newton and his
successors had accomplished in physics: it provided a purely natural
explanation for order and the appearance of design. It made the features of
organisms explicable by processes that can be studied by science instead of
ascribing them to miracles. The contemporary “intelligent design” movement is
simply a repetition of the predarwinian argument, and of course it cannot be
taken seriously as a scientific explanation of the properties of living things.