Theories, facts and laws

I'm a big fan of neurologist and renowned skeptic Steve Novella's blog Neurologicablog, and his latest post brought to light an issue that continues to be a big source of misunderstanding among the public. Novella details an email exchange he had with a creationist (identified only as "Duane") debating the facts of evolution. He has a saintly amount of patience with someone who is clearly in serious denial, and who repeats – in his own words – the old "evolution is just a theory" canard:
"...if it is a slam dunk then why is macro-evolution still a theory and not a scientific law?"
I'll resist the temptation to get into a big post about "macro-evolution" (I already did, a good while back) and instead address that common misconception: that "theory" and "law" is some sort of scientific hierarchy. People like Duane here apparently think that a scientific theory is just sort of a "best guess" or hypothesis, and once it's validated by thorough research it gets promoted to a "law". This isn't an isolated case of ignorance, of course, as those infamous little "disclaimers" about evolution's supposedly tenuous status as a mere theory being popped into public school science textbooks can attest.

The difference between a theory and a law is that a theory posits an explanation for observed phenomena that can be experimentally verified (or falsified), while a law is simply a repeatedly observed process that can be expressed in concise mathematical terms. From Wikipedia:
A law differs from a scientific theory in that it does not posit a mechanism or explanation of phenomena: it is merely a distillation of the results of repeated observation. As such, a law is limited in applicability to circumstances resembling those already observed, and is often found to be false when extrapolated. Ohm's law only applies to constant currents, Newton's law of universal gravitation only applies in weak gravitational fields, the early laws of aerodynamics such as Bernoulli's principle do not apply in case of compressible flow such as occurs in transonic and supersonic flight, Hooke's law only applies to strain below the elastic limit, etc.
A scientific theory, on the other hand, is a body of knowledge in which a testable mechanism is used to explain the relationship between observed facts. For example, it is a fact that chickens have inactive genes for producing teeth, and whales have inactive genes for producing legs. It's a fact that species throughout the world and throughout history share many physical traits, and do so in an apparently ordered fashion. Now, any hack can cook up some theory about why this is the case, but in real science it has to be empirically testable. In other words, it can't just purport to explain what we already know – it has to successfully predict what discoveries we will make.

A fine example of evolutionary science in action is the discovery of a fused chromosome pair in humans. Evolutionary theory says that humans and other modern primates, like chimpanzees, have a common ancestor. If that is true, we should have all the same chromosomes. But at a glance, that appears not to be the case – chimps have 24 chromosome pairs, and humans have only 23. So either that chromosome pair is there and has fused with other chromosomes, or the theory of common ancestry would be in trouble. Well, as the video below explains, we do indeed have that extra chromosome, and indeed it is fused.

That humans evolved by natural selection is a fact firmly established by 150 years of scientific progress in multiple independent scientific disciplines. It's also a theory – one of the most robustly validated scientific theories there has ever been.


  1. Thanks for this essay, Mike. I think that the strengths and limitations of the scientific method are very relevant to your discussions of the past. I'm wondering if you have any thoughts about the clarification of, and differentiation between science as a method of discovery and science as a philosophical structure. I'm not familiar with any such discussion, although within your discussions I've gotten the sense that science has been used in the context of the scientific method and as a philosophy that defines and filters knowledge.

    That's a tangent, however. At hand, I think that to deny the validity of the evolution model is to contradict observable data to such an extent as to be sadly misled. Research from the field of social psychology (I have a masters in psychology and am back at the university working on some more post-grad studie) has demonstrated that in instances when a person's deep held beliefs and attitudes conflict with observable facts an uncomfortable condition referred to as cognitive dissonance (pop culture has made us all aware of this term) occurs. Importantly, research has demonstrated that our attitudes and beliefs usually hold fast and remain unchanged in the face of observable facts. The facts are changed rather than the attitudes, in other words. This is due to a principle called 'cognitive indolence,' which is based on the premise that it requires less effort from the individual to remain in competition with facts than it does to restructure the established system of beliefs and attitudes, which, notably, have deep connections with the individual's sense of identity and security. Therefore, it may be helpful to recognize the cognitive dissonance, and the tendancy towards cognitive indolence when scrutinizing viewpoints, such as creationism, which fly in the face of what is so clearly observed. I'm sure everyone is more-or-less aware of these principles, but it's still meaningful to rehash, nonetheless.

    As scientists, I think we should strive to recognize our own cognitive dissonance, and to pursue objectivity, particularly when it comes to issues that touch upon our own beliefs and values. If and when we begin to harbor defensiveness and become argumentative, we are deviating from the ideal we hope to represent. It is likely true that indelicate confrontation will tend to extenuate the effects of cognitive dissonance and diminish the likelihood of facts prevailing in a discourse.

    Furthermore, as scientists, we should strive to understand the processes by which belief systems are formed, and therefore be empathetic, or even sympathetic for those who are in the bondage of oppressive belief systems and institutions. Moreover, the scientist should strive to respect the value of cultural diversity, and religious fundamentalism may be conceived of as part of some groups' cultural identity.

    In summary, my argument is that the most effect scientist as activist has achieved, through self-awareness, the ability to minimize his own congitive dissonance, to confront ignorance dispassionately, and to do so with a respect for cultural diversity and the predicament of those who are stuck in the bondage of insitutionalized belief systems which contradict observable data. The self-aware scientist will 'get through' more often and achieve more progress against ingnorance.

    I appreciate your discussions, Mike. I'll keep reading.

  2. Thanks Noah. You might be interested in this video, which talks about cognitive dissonance and how it's reconciled.

  3. We are all subject to our biases, even if we're coming from a position of proposed scientific objectivity. Such bias may cause us to be satisified with explanations which aren't really satisfactory. It's a tough balancing act to uphold reason and skepticism and to be objectively open-minded. (This is tangentially related to the evolution/creationism debate). Think of the 'scientists,' prior to advent of the microscope, who scoffed when a theorist proposed microorganisms. There was no evidence, yet the patterns the theorist observed led him to suspect that microorganisms best explained observable phenomena. The scoffing scientists upheld rigorous skepticism, but failed to be objective. Their biases dictated their interpretation of information. Even the skeptic must continue to strive for balancing critical thinking with open-mindedness and for objectivity.

    With that said, theology in general is far-fetched enough for me to discard as mythology. Evolution is easily the logical explanation of observed facts and patterns. But, as portrayed in the example of the theorist postulating microorganisms based on observed patterns, we must be humble enough in our thinking strategies to remain fluid in our belief systems. As soon as we contextualize information according to what we expect (or desire) to determine we are in danger of reaching invalid conclusions.

    So, the skeptic has not conquered bias by virtue of embracing skepticism. A good self-check may be to examine our own feelings of argumentativeness -- the greater they are, the more tenuous (or incongruent, to use client/human-centered theory) our position is.

    In that sort of a paradigm the evolutionist may have little to no visceral reaction to the creationist, but would have empathy for the phenomena, i.e. bondage to dogma, underlying the creationist's dilemma. Meanwhile, the evolutist patiently waits for the idealogy of society to evolve while offering his input, to shape its evolution, in the most constructive way possible.

  4. I don't think it's possible for us to eliminate our biases. We can take measures to reduce them, but the scientific method was designed for the exact purpose of removing personal bias from the search for and acquisition of knowledge. And I think science is, as you say, necessarily fluid. I don't think our best tool is certainty – it's methodology. I think that embracing skepticism isn't intended to eliminate biases, but to acknowledge them.


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