Apropos of Mike Huckabee & Ron Paul's evolution skepticism and its relevance to their political runs Andrew Sullivan has been posting a series of comments from readers about whether evolution and gravity are laws or theories. I am generally somewhat averse to these semantical debates, and more interested in the fundamental question as to whether one can be rational & informed and reject evolutionary theory. But what do readers and others ScienceBloggers think? I was taught that laws are empirically validated truths and rest upon induction. Theories are basically systems of highly validated sets of interlocking hypotheses and inferences. I also think that this sort of dichotomy makes a bit more sense in physical sciences than it does to evolutionary science. Nevertheless, I do think the last comment goes a little too far here:
"Evolution" doesn't have a law because there's just not a nice mathematical expression of it to call a law.
I don't think they're nice, and nor do they have the power of Newtonian mechanics, but the body of work produced by theoretical population geneticists isn't something that should be dismissed. Fisher's Fundamental Theorem of Natural Selection aims to characterize one parameter, while various stochastic models can handle drift and its affinal processes. These tools and heuristics aren't what anyone would wish, but they exist. Finally, just as theories of gravity have been used in practical circumstances, such as extra-planetary trajectories or projecting the arc of a cannon ball, quantitative insights premised on evolutionary assumptions lay at the heart of much of agricultural science (e.g., animal breeding and so forth).
Update: John Hawks has the goods. When I see some evolutionarily influenced thinkers posit "laws" I do tend to roll my eyes thinking back to their proliferation in late 19th century biology....
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You can be precise, and concise, without invoking mathematical formalisms.
Evolution and gravity are both facts. The descriptions of our explanations for these facts are theories. a = GmM/r^2 is a law.
In the strict scientific sense, there is no law of evolution. Although there are laws for subphenomena of the field. But that's not the context in which that phrase tends to appear.
I've always liked Feynman's "The Character of Physical Law" as far as explaining the nature of scientific law without falling into a long talk about semantics.
Due to its statistical nature, evolution and biological processes will never have the precision of physical laws, but if economics can get away with laws, I think a relatively low bar of empirical validation has been set.
I think the basic mistake that people who make the "it's a theory not a law" assertion fall into is that laws are theories that have been proved out over time. I seem to recall a few textbooks back in my elementary school days that actually asserted this -- and given that many people in this country don't have a science education that goes beyond an elementary level, that's probably where most people still are.
I would tend to characterize evolution as a theory rather than a law, but in this sense: It seems to me that laws tend to be basic descriptions of what universally seems to be the case, which don't necessarily make any attempt to say anything about mechanism.
The classic example of Newton's laws of motion fits this pretty well. The laws of motion described how bodies universally were observed to move, but they didn't make any attempt to explain why.
Evolution encompasses a wide range of theories, but all of them deal quite a bit with mechanism, and can be proved out and examined based on their predictive and descriptive power. But since it deals with mechanism rather than basic "this is how it appears to be" statements, it seems to me that evolution is more composed of theory than law.
"Law" has a very old history. Kepler's "Laws" of planetary motion were empirical observations that predicted the motions of the planets in a helio-centric system. They were ways to do calculations. But nothing explained why the law had the particular functional form until Newton. From Newton's *Theory* of Gravity, you could derive Kepler's Laws. The Laws lacked explanatory power that the more fundamental theory posessed.
This is where our language trips us up. People expect that "Laws" are more important than "Theories" because they sound more important. In fact, it's the other way around. A Theory is more valuable than a mere Law because it has explanatory power. It tells you *why* the Laws posess the functional forms they have.
In response to evolution being able to be expressed mathematically: Even if we can create formulas to express aspects of evolution, it cannot be a law because these aspects of evolution are normally things like "tendencies" (beneficial variations TEND to be chosen) and aren't universally consistent like the speed of light for instance.