Theories do NOT become laws

Michael Doyle’s post about evolution and students’ acceptance of evolution brings up another misconception about how science works. Many (most) people believe science ideas progress through a hierarchy.  They believe ideas begin as hypotheses, then with some evidence they become theories and finally, when the evidence becomes overwhelming, the idea becomes a law.  Without any hesitation: this hierarchy is WRONG!!!!  The difference between theories and laws has nothing to do with how much evidence supports each.  The difference also has nothing to do with how well the idea is accepted in the scientific community.

Theories cannot become laws because each serves a different purpose.  Let me explain (and yes, this is a simplified explanation). Theories are a set of ideas that help to explain how or why natural phenomena occur.   Laws are usually mathematical relationships that describe what happens.

Perhaps some examples will help illustrate the points.  The Gas Laws are mathematical formulas that describe what happens in the natural world.  For example, the Gas Laws predict with great accuracy that if I double the temperature of a sealed gas (at constant volume) the pressure will double.  This relationship is mathematical and tells me what will happen; therefore, this idea is a law. However, to explain why gases behave this way we must utilize kinetic molecular theory.  The particles of a gas bounce off of one another in elastic collisions (think billiard balls in 3D).  If we double the temperature the tiny spheres move twice as fast and collide with the container with double force.  This double force exerted on the container results in double pressure.

Neither of these ideas (gas law or kinetic molecular theory) is more accepted than the other.  They are both useful for understanding matter.  The theory is not below the law.  In many ways, the theory is more useful than the law because it tells us why something happens, not just that it does happen.

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Now let’s apply this to evolution.  Oftentimes, people dismiss evolution because they believe it to be “just a theory”.  Yet, according to the above, a theory explains how or why something happens.  The explanation is the part that Darwin provided (“evolution” predates Darwin).  Darwin provided a mechanism, a “how” for evolution. Darwin’s theory of natural selection is not a theory because it does not have sufficient evidence, it is a theory because it explains how species evolve.  So evolution by natural selection is not “just a theory”, it is the most empirically supported, scientifically accepted, way to explain how species evolve.

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For those who really want a stretch let me pose some questions:

1) If laws are usually mathematical, does biology have laws other than Mendel’s?

2) Considering that theories are “sets of ideas”, in what way do theories make use of laws?