Thursday, March 4, 2010

Evolution - "Just" a Theory

The dinosaur story reminded me of creationists and those who support Intelligent Design as alternatives to evolution, and call evolution just a theory, implying it isn't tested or true.  In fact, it is both tested and true.  I quote at length here from the book Why Evolution is True by Jerry A. Coyne (NY: Viking, 2009, pp. 15-16):

"According to the Oxford English Dictionary, a scientific theory is 'a statement of what are held to be the general laws, principles, or causes of something known or observed.  Thus we can speak of the 'theory of gravity' as the proposition that all objects with mass attract one another according to a strict relationship involving the distance between them.  Or we talk of the 'theory of relativity' which makes specific claims about the speed of light and the curvature of space-time.

There are two points I want to emphasize here.  First, in science,a theory is much more than just a speculation about how things are: it is a well-thought-out group of propositions meant to explain facts about the real world.  'Atomic theory' isn't just the statement that 'atoms exist'; it's a statement about how atoms interact with one another, form compounds, and behave chemically.  Similarly, the theory of evolution is more than just the statement 'evolution happened': it is an extensively documented set of principles... that explain how and why evolution happens.

This brings us to a second point.  For a theory to be considered scientific, it must be testable and make verifiable predictions.  That is, we must be able to make observations about the real world that either support it or disprove it.  Atomic theory was initially speculative, but gained more and more credibility as data from chemistry piled up supporting the existence of atoms.  Although we couldn't actually see atoms until scanning-probe microsopy was invented in 1981 ...scientists were already convinced long before that atoms were real.  Similarly, a good theory makes predictions about what we should find if we look more closely at nature.  And if those predictions are met, it gives us more confidence that the theory is true.  Einstein's general theory of relativity, proposed in 1916, predicted that light would be bent as it passed by a large celestial body... Sure enough, Arthur Eddington verrified this prediction in 1919 by showing, during a solar eclipse, that light coming from distant stars was bent as it went by the sun, shifting the stars' apparent positions.  It was only when this prediction was verified that Einstein's theory began to be widely accepted.

Because a theory is accepted as 'true' only when its assertions and predictions are tested over and over again, and confirmed repeatedly, there is no one moment when a scientific thory suddenly becomes scientific fact."

The book goes on to detial how evolution has been tested and proven and how it has predicted things that turned out to be factual.  So, to recap, evolution is a theory, but has been well tested and found to be true.

Another point to remember is that intelligent design can never be a scientific theory, because it posits something supernatural, which can never be tested by science, which cannot measure that which is not of the natural world.




Posted via web from reannon's posterous

No comments: