Feb 02 2010
Dawkins’ Book: The Facts of Evolution
Whoa! In a previous post about Dawkins’ book, didn’t I criticize the use of “fact” to describe the Theory of Evolution? Yes I did. How then, in the title to this post, can I refer to the facts of evolution without contradiction?
Allow me to explain. The philosophical wordsmith in me believes that a theory cannot be a fact. While a theory can be be true, or valid, or empirically substantiated beyond the shadow of a doubt (as in the case of the Theory of Evolution), theories belong in different categories than facts.
So no, I don’t believe it is contradictory to refrain from referring to evolution-theory as a fact, but freely refer to the empirical measurements and observations that evolution has occurred as facts.
Dawkins himself illustrates the difference by using this metaphor throughout his book: a detective objectively examining the evidence for evolution will surely come to the conclusion that evolution is a fact.
What are detected? Facts. What is the result? A conclusion. However, I do stop short of calling a conclusion a fact. Yet there are undeniable facts supporting the conclusion. If Evolutionary Theory itself were the case of a simple fact, would you need a detective to detect it?
One of the things Dawkins’ book does extremely well is to share some of the most substantial facts that reveal evolution to us. Bits of evidence that lead to one conclusion. Evolution is true.
In Chapter 5, “Before Our Very Eyes,” of his most recent book, The Greatest Show on Earth: The Evidence for Evolution, Dawkins presents evidence of evolution in our time. And the cases of bacterial evolution and guppy evolution are very compelling.
Evolution on a Petri Dish
Richard Lenski & co. followed not 2 nor 20, but a mind-boggling 45,000 generations of bacteria in their lab. As a selective pressure — a “fitness hurdle” that the evolution of the bacteria surmounted — they manipulated the food supply, the amount of glucose in the environment. This was a controlled experiment. A test. And evolution passed the test. Undeniably so. Read the account in his book. You’ll be impressed.
Evolution in a Stream and Lab
In another bit of slam-dunk research Dawkins shares, an experiment produced measurable phenotypical change in populations of guppies. In as little 9 months! The presence of predatory fish provided the fitness hurdle subsequent generations of offspring were “selected for” (a problematic term, for no external agent did any selecting).
What about the fish changed? The average number of male decorative spots, the overall size of the fish, and the number of offspring. In both the predator-free and predator-limited environments, the fish grew larger and had fewer offspring of larger size. This is a distinctly different reproductive strategy, at least on the spectrum of “fewer with greater chances of survival vs. or more with lesser.” Additionally, it seems sexual selection favored spots in the males. But only in the predator-free and predator-limited stream environments. This is a great example why we speak of selective pressures. Just as sexual selection is not an all-or-nothing proposition, neither is the selective pressure applied by the presence of predators. Every generation lives and dies within an environmental context replete with pressures, plural. Which are the most important? Wait a generation and the answer may change.
Very significantly, the guppy study has been replicated in a controlled lab environment. Experimenters manipulated a variable, the presence of predators, to see if it would cause change in another — the phenotype of the small fish. It did.
The Conclusion
There is only one sensible way to describe what happened to those many generations of bacteria and guppies: They evolved. It is an inescapable conclusion. No denying it.
Evolutionary theory passed those two tests described above. As it has many others. You reasonably say say that controlled experiment has confirmed the validity, the truth, of Evolutionary Theory.
What test has any other theory about the origins and development of life on Earth passed? None. And that speaks volumes.
