Why is evolution a theory and not a law?

A few months ago, while discussing my frustrations with the anti-evolutionary ideology that’s presented in the homeschool program my son is part of, my friend raised a good question. As I recall, I was venting about the kinds of ideas that are promoted in anti-evolution circles that are demonstrably false, and my friend asked a question along the lines of, “If the evidence for evolution is so overwhelming, why is it considered a theory and not a law?” He brought up the “law of gravitation” by way of contrast.

My friend does not come across to me as ideologically anti-evolution. He is very well-read biblically and theologically, so I don’t think he is drawn to the kind of Bible interpretation that leads to YEC ideas. But I think he also has acquaintances with advanced science degrees who have told him that the scientific evidence does not support evolution. I certainly don’t think he was trying to play the “just a theory” canard; he was just asking an honest question. In the end, he said this is not an issue that is “front-burner” for him, so he just hasn’t given it much thought. That’s essentially the perspective I had for many years and perhaps still would if homeschooling hadn’t pushed the issue on me.

So, I’m wondering if some of the scientists around the forum can speak to these questions. Why isn’t evolution considered a law? What would it take for it to be one? Can you see this happening the next few decades as the evidence accrues? Is it the case that a theory becomes a law when the evidence reaches some critical “tipping point”, or is it not that straightforward?

As a final note for any who are inclined to respond to this question along the lines of “because there is no evidence for evolution, and those who say there is are deceived or trying to deceive others because they adhere to a godless philosophy,” I respectfully request that you not engage in that discussion on this thread. The battered carcass of that horse can be examined in many threads on this forum. And it seems that Chris, Hugh, Steve, Josh, and others have inexhaustible patience in explaining the evidence for evolution to those who are willing to dialog and learn (and, yes, to some who are not so willing). I think those discussions are valuable. I’d simply prefer that this thread remained focused on one issue: given the strength of the Theory of Evolution, why has it not risen to the level of a scientific law?


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I wish I could take credit for a good answer, but I used Google and found this link:

For a very quick explanation, here is a quote from the page:

“In general, a scientific law is the description of an observed phenomenon. It doesn’t explain why the phenomenon exists or what causes it. The explanation of the phenomenon is called a scientific theory. It is a misconception that theories turn into laws with enough research.”

For these reasons, we still have things like “Germ Theory” and “Cell Theory” (and “Evolutionary Theory”, of course) that will not eventually morph into Laws, given enough time.


That argument has been discussed many times here and elsewhere. It is based on the common usage of the word ‘theory’ as equivalent to ‘wild guess.’ Even a scientific hypothesis is the result of observation and application of current knowledge about the phenomenon at hand, not just a wild guess.

The closest thing to a ‘law’ we have in evolution is that a species must adapt or go extinct when its environment changes. Since we can never predict which species will go extinct or how it might adapt, evolution will always be a theory, as defined by science. That does not give the ToE any less weight as an explanation for the change we can observe in the fossil record.

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Maybe one reason is that “law” is more of an informal term used in popular discourse or as a shorthand term by scientists speaking informally to each other or to the lay public. Since all conclusions reached scientifically are held as provisional at least to some degree, it is only a perspective from hubris that we call things “laws” as if our understanding of them is now above any possibility of revision.

Of course I must add that we certainly teach laws all the time in science education. So we are exhibiting a hubris on the part of long-established consensus, and rightly so as students need to respect and appreciate what they would be up against if they, for example, think they can invent a gizmo that delivers more energy than it consumes. The “1st law of thermodynamics” isn’t a prohibition telling them this will never be done and they shall not attempt this so much as it is an observation that it has never been done before despite many attempts.

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I discuss this issue at length at the beginning of the Evolution Basics series. The short answer is that theories do not become laws - but read the linked article to see why.


The biggest reason is the linguistic and idiosyncratic history of biology. We do not really have any laws in biology. That is just not the way we discuss the patterns we find in biology, even as we approach 100% certainty about things. Instead, we have “dogmas”, “theories” and “rules”.

Secondly, for the vast majority of “rules” in biology, there are exceptions that (1) are quickly discovered, and (2) too important to be neglected. This means that the “laws” are not a dominant metaphor at all.

Third, if one was to try and think up “laws of Biology”, even though we do not use that language in biology, evolution would be called be called law. See for example: http://hunblog.typepad.com/hunblog/2006/09/four_laws_of_bi.html https://link.springer.com/article/10.1007/s11270-008-9925-3

Fourth, even in physics there is a distinction between (1) the Laws of Gravity and Planetary Motion and (2) the exact configuration we see planets in the solar system, which depends also on initial conditions and historical contingency. In fact, there are even proofs that without perfect knowledge, approximates based on partial information cannot reproduce the full system’s dynamics (see chaos theory), which makes many physical systems (e.g. many-body systems) intrinsically unpredictable, even though they arise from laws.

Similarly, there are certainly law-like things in evolutionary biology (e.g. neutral theory), but they include strong dependence on initial condition and historical contingency. Many of the questions we care about fall into the non-law-like category which might explain why “laws” is not part of the standard biology lexicon.

Any how, that is a good question. I’d just emphasize that “laws” is not a measure of certainty in a theory. That is not the language of biology.

interesting link on the laws of biology.

“The Second Law of Biology: all living organisms consist of membrane-encased cells. Enveloping membranes allow physical separation between the living and the non-living worlds. Viruses, plasmids, transposons, prions, and other selfish, biological entities are not alive. They cannot “self” reproduce. They are dependent on a living cell for this purpose. By definition, they therefore, are not alive.”

This shows a significant limitation of the authors in defining life in the first place. A virus is very much alive if it has the ability to reproduce itself even if using another cell to do so. and ability to self reproduce is not a prerequisite for life as a terminal differentiated cell as well as a mule that cannot reproduce itself any more is still very much alive. In fact, those terminally differentiated cells in the immune system are quite essential for life to go on.
Life is the ability to move energy and matter at will, a will that is encoded at the genetic level in the case of a material entity and at the intellectual level in humans. Thus if in “thy will be done” I execute the will of God in Jesus Christ.s name Jesus as well as God is very much alive.
How we deal with life in silico will be an interesting question from a biologists perspective and how to explain the contingency.
The law of evolutionary fitness “to love thy neighbour like thyself” has lead to reality that is driving towards increasing system complexity, as evident in the interaction of the planets in our solar system, the complexity of ecosystems on this planet and the complexity of the human being with its ability to comprehend said complexity on a non genetic level. However, this ability of comprehension has left us with a huge responsibility, as to understand the law of evolution and existence makes us morally responsible for our actions in accordance with the law. In that respect the authors of your article got it right, the law of nature cannot be broken. To do so leads to elimination from nature.
“They do not understand that natural selection is cruel and can cause immense suffering and death.” only shows the logic incoherence of the authors. Gods judgement or the laws of Nature as they call them, implying that nature can make laws :slight_smile: is not cruel, but just. in causing the death of those that fail to love thy neighbour he prevents suffering and death of those he loves equally. As long as we do not accept Gods judgement, e.g. his authority over “Nature”, we will carry on to perceive his judgement as cruel because we do not accept his will to be done.

The biggest blunder comes in the end when they claim:
"the first step in this direction is to understand the basic laws of physics, chemistry, and biology and how they govern our biosphere, which is currently under assault and in need of being rescued. However, without profound respect for Nature and compassion for life, all life, knowledge is likely to be insufficient. We must develop into more caring, sensitive, and compassionate beings."
The more logic sequence was phrased by some bloke a couple of thousand years ago who some claim to have been a a primitive goat herder who just did not know any science - or even to be a figment of human imagination :
“‘Love the Lord your God with all your heart and with all your soul and with all your mind. This is the first and greatest commandment. And the second is like it: ‘Love thy neighbor as thyself.’ All the Law and the Prophets hang on these two commandments.”
In other words, how do you claim you can understand the law if you do not understand it’s premise? What happens, if you don’t, is, that you call evolution cruel and the cause of suffering or try to define the process or theory as a law instead of realising that a process is ruled by a law. In order to avoid to consider a law maker, materialists even believe that a process is a law, or can causes its own law, but then if they are scientists they must of cause know better. :slight_smile: Luckily not all scientists are the same, but then if they love science with all their heart and all their soul and all their mind there is nothing left to love with, so they are stuck with a cruel process.

Thanks, everyone for your contributions here. While this hasn’t cleared up everything about this topic for me, what does seem evident is that the answer to this question…

… is “no, it is not that straightforward.”

I’m still interested in learning more about the way the term “law” is used within scientific discourse, but I found the article that Curtis pointed me to helpful. It does still seem that there is a grey area between theories and laws that leaves room for subjective judgment and rhetorical effect to influence the word choice.

Somewhat related to this topic (though in the other direction), I spend time looking at curriculum descriptions for various schools and educational programs, often trying to discern what the approach to science education is. A classical Christian school in the St. Louis area lists as part of their biology course “an introduction to Darwin and his Evolution Hypothesis”. I found that quite revealing.


Incredible, isn’t it? How so much meaning can be packed into a single word choice?

The use of the term “law” in the natural sciences is difficult to use with precision because it is a general term used to refer to various aspects that includes rules and observations. Normally we use it in science to refer to a statement of fact from observations (data) that will always occur given certain conditions. The easiest example is found in “laws” such as the area of a circle (A=pir^2), a right angled triangle, and such objects. The criteria must be that data can be obtained directly, variables are removed, or at the very least accounted for, and a mathematical formulation can be provided (more for detailed examinations and testing as much as precision).

The conditions imposed for “law” cannot be easily met, and the complexity in biology mitigates against “laws” as normally understood (or they may be obvious statements that have little utility, such as a species must live to survive).

Most of the time, scientists (I speak more for myself) prefer the term “JBlogg’s theory” and this allows a scientist to question and devise experiments to show the limitations of such a theory.

In any event, science nowadays has become so specialised, and the techniques often so exacting, that discussions of any particular “law” are often confined to a few specialists in a field.

We do have the Mendelian laws of inheritance. Goes to show there’s a real difference between Mendel and Darwin.

Have you considered that while Mendelian genetics can readily be verified experimentally and has real and immediate implications in medicine, biology, food science and much more, the “knowledge” that organism A evolved from organism B, or the two are just products of “convergent evolution”, adds nothing to our understanding of either A or B? More… http://nonlin.org/mandatory-evolution-statement/

Except Mendelian “laws” are not really laws because there are numerous important exceptions. You are making my point for me @NonlinOrg. =)

Except Mendelian genetics has not been “verified” as a “law.” It is just a general rule, that is frequently violated.

And evolution is how we understand cancer. It is extremely important to how we treat it.


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