Philosophy of the Sciences, 1997
Lecture 8: Evolutionary Theory and Creationism I
Summary
-
1. If the Book of Genesis is literally true,
then modern evolutionary theory is false. Scientific Creationists
are Christian fundamentalists who believe in the literal truth of Genesis,
and think that they can prove the biblical story to be better supported
by evidence than evolutionary theory. Because, in a way, they are
crusading for God, these Creationists have gained the support of a great
number of religious people and, in many states of the U.S.A. laws have
been passed requiring the teaching of Creation Science in schools.
go to summary
-
2. Philip Kitcher, in his book Abusing Science:
The Case Against Creationism (Milton Keynes, Open University Press,
1982) argues that there is no scientific evidence to support the Genesis
story. He defends evolutionary theory against the Creationists' attacks,
and in Chap. 5 examines the positive theory that Creationists have to offer,
and finds it worthless. The general value of examining this
dispute is that by exposing pseudoscience, we get an insight into
the nature and methods of science.
go to summary
-
3. Non-biologists should read Chap.1 (`Evolution
for Everyone') of Kitcher's book. It provides the small amount of
information necessary to be in a position to evaluate the dispute.
For present purposes, what we need is the concept of a gene -- the
pattern in cells transmitted from one generation to the next which determine
the characteristics of an organism and alleles which are the alternative
forms that genes can take -- so (Kitcher's example, p.10) the gene for
blue eyes and the gene for brown eyes are alleles of the gene for eye color.
go to summary
-
4. First, we shall consider the
attacks by Creationists on evolutionary theory.
One common accusation is that evolutionary theory is not proven, therefore
it has no scientific status. So, say Creationists, believing in evolution
is just a matter of faith -- and why should we prefer children to accept
this faith rather than religious faith ? The answer to this
is that `science is not a body of demonstrated truths' (p.32), yet there
is a world of difference between believing a theory for which we lack conclusive
proof and just accepting some claim on faith. The whole history of
science is testimony to human fallibility, yet there is nothing unreasonable
in believing to be true a theory for which we have overwhelming (but not
conclusive) evidence. Against Creationists' claim for parity, Kitcher
observes that `all theories are revisable, but not all theories are equal'
(p.34)
go to summary
-
5. Creationists charge evolutionary theory
with predictive failure. This charge can come in three varieties,
which Kitcher usefully distinguishes (p.38). Perhaps the favourite
ploy is to adopt Popper's criterion of unfalsifiability and to argue that
evolutionary theory is unfalsifiable and therefore unscientific.
Kitcher has a useful demonstration that the unrefined Popperian view on
which Creationists rely is untenable. The reason is that, if we come
across what seems to be a predictive failure of a certain theory, we can
always say that some unforeseen force was at work to produce that unexpected
result. Hence any theory is unfalsifiable.
-
6. We might try to answer this objection by pointing out that hypotheses
are not falsified singly, but come embedded with a lot of other assumptions,
and that the whole bundle of statements does have observable consequences
so that evolutionary theory, considered this way, is falsifiable and hence
respectable. The trouble with this way out is that, by adding assumptions
to any statement, however crazy or nonsensical, one can produce
a bundle with testable, i.e. falsifiable consequences. So the criterion
is too slack: it allows us to count nonsense as scientific. So this
kind of falsificationism -- which Kitcher calls `naive falsificationism'
is useless. Therefore Creationists are unwise to wield naive falsificationism
against evolutionary theory, since that criterion can show that any science
is not a science; hence it is that criterion that is at fault. Of
course, the corollary to this, as Kitcher notes (p.44), is that scientists
should not use the criterion of naive falsificationism as a means of rejecting
Creation Science as unscientific.
go to summary
-
7. By considering the example of Newtonian
mechanics, Kitcher identifies certain criteria for a successful science:
independent testability, unification and fecundity (p.48). In other
words, there is much more to successful science than the making of predictions;
what we require also is the furnishing of explanations. So the question
is `Does evolutionary theory satisfy the above criteria for being good
science ?'
go to summary
-
8. Kitcher answers `Yes'. If we want
to know, for example, why a contemporary creature possesses a certain trait,
we supply a Darwinian history which describes how that trait emerged.
Similarly, to find out why two species share a particular trait, we may
trace their descent from a common ancestor (p.50). We can explain
why certain species became extinct by showing how characteristics that
were beneficial to their survival were no longer effective when a change
of environment or a change of competition occurred.
-
9. Kitcher lists a small selection of the questions
that modern evolutionary theory has been able to answer: `Why do orchids
have such intricate internal structures ? Why are male birds of paradise
so brightly colored ? Why do some reptilian precursors of mammals
have enormous `sails' on their backs ? Why do bats typically roost
upside down ? Why are the haemoglobins of humans and apes so similar
? Why are there no marsupial analogues of seals and whales ?
Why is the mammalian fauna of Madagascar so distinctive ? Why did
the large carnivorous ground birds of South America become extinct ?
Why is the sex ratio in most species one to one (although it is markedly
different in some species of insects) ?' If we look at the details
of the answers to these questions, we see that evolutionary theory provides
a unified account of all these phenomena; the theory meshes in with
geological accounts of changes in the environment and with other independently
verifiable scientific theories, and it gives rise to important new areas
of scientific investigation. Darwin himself acknowledged that there
were many questions to which he did not have the answers, but he initiated
a research programme, and many of the answers to those questions are now
known. His theory spawned other areas of enquiry (such as sociobiology).
In short, the theory satisfies our criteria for good science.
go to summary
-
10. In Chapter 3 of his book, Kitcher considers
the tautology objection to evolutionary theory. Basically the objection
is this: Evolutionary theory is the Principle of Natural Selection.
This is the principle that the fittest survive. But what do evolutionists
mean by the fittest ? They mean: those that survive. So evolutionary
theory reduces to the tautology that those that survive, survive.
Kitcher's first point against this is that evolutionary theory is not to
be identified with the single statement: the principle of Natural Selection.
First, there is no such single principle -- evolutionary theory is a body
of principles or, as Kitcher puts it (p.58) a collection of problem-solving
strategies that use Darwinian histories. Second, the concept of fitness
is not to be identified with the number of offspring that an animal produces.
In fact, in modern evolutionary theory, fitness is not a property of organisms,
but of genes, specifically, the fitness of the allelic pairs that
make up an organism's genotype. Third, with this more sophisticated
understanding of fitness, we can look to one part of modern evolutionary
theory, namely mathematical population genetics, to give us precise, non-tautological
probabilistic results about the survival possibilities of various allelic
pairs.
go to summary
-
11. Another type of charge levelled against evolutionary
theory (again, this is a Popperian point, although Kitcher doesn't say
so) is that the theory is just too adaptable -- it is so flexible that
it can accommodate itself to any new observations. This is not a
virtue; if the charge is admissible that would mean that Darwinian theory
lacks content. As Kitcher puts it (p.61) `a theory that is compatible
with all results explains none'.
-
12. But is the charge justified ? Kitcher thinks not.
Darwinian histories are subject to numerous checks. Some creationists
deny this independent checkability. They claim, for example that
geological dating of rock strata is determined by what fossils are found
in those strata, and that the dating of those fossils depends on evolutionary
assumptions about the dates of the organisms fossilized in the rocks (p.63).
So the Creationist says that the geological record offers only a circular
justification of evolutionary theory. But, as Kitcher points out,
this is a complete misrepresentation. The geological system for dating
rock strata predated Darwin's theory, and it was assumed that organisms
found in lower strata had flourished before those found in the upper strata.
But there was no commitment to the view that the upper strata organisms
had evolved from the lower. And we now have plenty of independent
methods of dating rock strata (e.g. radiometric testing using radioactive
decay).
-
13. If, over the course of time, there is gradual
adaptation to the environment, as evolutionary theory predicts, then it
would seem that there should be a continuum of living forms -- there would
be no biological categories. But there are such categories. Hence,
Creationists say, evolutionary theory is false.
-
14. The answer to this is that evolutionary theory does not predict
such a continuum. An ancestral species may split into two that then,
by natural selection, go separate ways (p.68) resulting, after millions
of years of evolution, in two morphologically very different populations.
The original splitting into two can come about, for example, when a group
of organisms gets geographically isolated from the rest of the population
and gets subjected to different environmental pressures.
GO BACK TO COURSE
OUTLINE