My science education ended in high school. The course work was solid and challenging for high school but still lacked the depth and rigor of a college program.
In the biology class, the teacher explained the scientific method. He later touched on the debate over evolution and creationism in a short speech like this: “Evolution is both factual and theoretical. Species change. That is the fact of evolution. This change is explained by natural selection. That is the theory of evolution. It is the best working explanation.” That was about all he explained about the debate. There really wasn’t any debate in the class. We all accepted that creationism was BS and no one dragged out the discussion.
I’ve accepted this for the past twenty years. Now that the debate is making the news again, I wonder if we got the correct and complete story.
My questions: Is the teacher’s explanation of what is fact and what is theory correct? For an educated and sane biologist, is there a distinction between evolution as fact and theory? When people debate “the theory of evolution,” are they discussing the process of natural selection or the broader changes in species?
Yes, there is a distinct difference. Think of it like you’d think of gravity. Gravity is a fact: when you let go of your coffee cup, it drops to the ground. Gravity is also a theory: any two masses attract each other based on their size and distance from each other. So evolution is a fact: species change over time. The how of how it does this is the theory part.
I think your teacher did an admirable job. Think of it this way: when a science person says “theory,” in your head, substitute “big-picture explanation.” That species evolve is a fact. The big picture explanation of it, mutation and natural selection, is called “theory.”
The thing is, when people claim “evolution is only a theory”, they’re actually making a stronger claim than they mean or than is warranted. In my observation, they’re trying to claim “evolution of humans is only a theory”. Which it is, as it has only happened once (I would think) and no one was there to witness it.
Your teacher was right, but it might have helped to include a discussion of the difference between a hypothesis and a theory. When creationists say evolution is “just” a theory, what they mean to say is that it’s just a hypothesis, which in point of fact is incorrect. In science, you don’t get any better than “theory”, and there is no operational difference between a well established theory, like evolution, and a fact.
Right idea, but the second part is also the fact of gravity. The theory of gravity is an attempt to explain why your coffee cup falls towards the center of the earth.
It’s a fact because we have tons and tons and tons of evidence showing that it happened.
Think of it this way. Someone might say “That the Civil War happened is a fact.” But you might say that we don’t really know it happened, since no one around today witnessed it. We have lots of documents and artifacts, but those could have been hoaxed, or misinterpreted."
Ridiculous, right? But it would be millions of times harder to hoax/misinterpret the evidence for evolution than for the Civil War actually occuring.
Partly because the alternative is even less credible. We have evidence completely independent of biology that the Earth and universe are extremely old (geology and astronomy, for example) and assuming that species had existed unchanged all that time, or came into existence on a four billion year-old Earth only recently (~6000 years, for example) makes even less sense than gradual evolution.
The use of the word “Theory” also has roots in the, ahem, evolution of scientific thought.
There are many “Laws” in science - Newton’s Laws of Gravitation, the Laws of Conservation of Mass and Energy, the Laws of Thermodynamics, etc. They all come from an earlier era in science, when people thought they were coming up with absolute descriptors of the way the world worked, absolutes that worked in all cases without exception.
As scientists gained understanding about the universe as a whole, they began to realize that reactions that held under normal conditions on earth were not so absolute after all when all the vast conditions of the universe were taken into account. The individual “Laws” of Mass and Energy had to be combined into the Law of Conservation of Mass-Energy, e.g.
So naming these rules as "Laws’ died out in the latter half of the 19th century. Instead, scientists began to use a capital T Theory as a descriptor of overarching explanations of behaviors. These theories were no less encompassing than the old laws, but there was less hubris involved. Future discoveries could prove that they weren’t the final answer after all. Einstein’s General Theory of Relativity didn’t overturn Newton’s Laws of Gravity; they merely showed that Newton’s equations were a special case of a more inclusive set of equations. If Relativity and Quantum Mechanics are ever successfully combined, then Einstein’s equations will be shown to be a special case as well. Not wrong - they’ve passed every one of a million tests over 100 years - just limited to a certain set of conditions.
And The Theory of Evolution is set up similarly. If we find life on other planets, perhaps, we may need to revise our understanding of the way the evolution takes place. This will not falsify evolution in any way: it will still apply to our local conditions on earth as well as it ever had. But nothing in science is ever assumed to be the final answer, unalterable by future discoveries. That’s what separates it from purely religious doctrines like Creationism or Intelligent Design.
In the case of simple animals, incidentally, this is false. Despite the frequent creationist claim to the contrary, speciation (the change from one species into another) has occurred in the lab on an apparently large number of occasions. This link:
will give you a starting place to a bunch of references (as will a simple web search if you prefer to find the cites yourself.) It also goes into the difficulty of defining the word “species,” which is interesting in and of itself.
Evolution doesn’t have to take millions of years, it just usually does.
Short answer: evolution doesn’t take millions of years. Evolution can be observable in as little as one generation. If you’re dealing with a species that only lives a few weeks, or a species that has been tracked in a controlled environment for many decades (or both), you can have a lot of data.
The observed evolution in this case isn’t going to be of the “dog evoluting from a dolphin” variety… it does provide real world examples of how evolution proceeds and, at least swince the modern synthesis, how evolution leaves its sticky handprints all over the genome.
So we can look at how evolution creates patterns in the genomes of organisms sharing common ancestry (all documented), and notice that we observe these same kinds of patterns in all life on earth. That’s where the theory comes in. We don’t know that humans and chimps are more closely related than chimps and gorillas… but given what we have observed of evolution compared with what we have observed about the genomes of chimps, humans, and gorillas, it certainly seems to indicate that conclusion.