As part of my undergrad studies we need to gain an understanding of what science is, what it is not, and – if it is science – how to determine if it is good science. Not all scientific theories are created equal and there are ways to evaluate how good a theory is. Some of the ways involve hard criteria such as leveraging probability and statistical analysis, and some are softer. It’s the softer ones that interest me today.
In biological science, the mother of all theories is Darwin’s theory on the origin of the species through natural selection (usually referred to as ‘evolution’). I’m going to use this theory as a framework to provide examples of what makes a good theory. The theory of evolution through natural selection is a good theory, and here’s why.
Good theories are simple.
Complicated theories are not desirable because they do not easily explain phenomenon properly and that makes it less available for other scientists to validate and build upon. It also makes it much harder to explain in the pub.
Darwin’s theory of how evolution occurs is this: every time cells are copied, a small number are copied imperfectly . This means offspring are slightly different from the sum of their parents and that can mean three possible outcomes:
- If this difference is detrimental, it will likely prevent the offspring from mating so the change will be lost forever.
- If this difference is neutral, it will not hinder the offspring’s ability to mate so the change will probably be carried on into future generations at a normal rate.
- If this difference is beneficial, that’s when fun stuff starts: this guy will out compete its peers for food (so they starve and die) and has a better chance of reproducing more. This means this change will be carried into future generations at an accelerated rate (more offspring AND less competition)
The last two examples imply that species change over generations. Simplicity itself.
Keep in mind that in Darwin’s time nobody had any real clue about genetics and the world was 50 years away from even discovering DNA existed, never mind understanding its purpose which did not come until over a century later. In the intervening time until today, many scientists have brought modern tools to bear and have validated Darwin’s theory time and again.
Good theories are general.
If more than one theory can explain a phenomenon then the one that explains more should be chosen.
Darwin came upon his theory by observing finches in the Galapagos islands in the early 1800s. He noticed that although there were finches on all the islands, their beaks were very different. The finches that lived on islands where bugs were the main food supply had long thin beaks which were effective at extracting bugs from crevasses. The finches that lived on islands where nuts were the most populous food had shorter beaks more able to crack nuts.
Once Darwin had properly fleshed out his theory he realized that every living thing in the planet could have evolved in the same way. The beaks were just examples of advantageous mutations that were preserved and the finches born with unsuitable beaks for their island perished and their mutations lost.
If Darwin’s theory only explained why finches had different beaks in the Galapagos, that would be a very specific and therefore less useful theory. The fact that it can explain the current structure of all life makes it a very general and therefore very useful theory.
Good theories allow predictions.
It is a hallmark of human intelligence to ponder “if this means that, then it must also mean this other thing. Let’s check.” In Darwin’s case, if his theory of how finches got their beaks is correct, then we should be able to predict and find examples of generational adaptation in other life on Earth. In practice this is a terribly hard thing to do because adaptations take millions of generations to manifest enough to be measurable. For us long-lived humans that is a long time span. However, there are some short-lived life forms on Earth that can help us.
Mosquitoes in London turned out to be a good example. During WW II, the London tube was used for air strike protection. When the air raid sirens sounded, everyone went down into the tube and the mosquitoes down there had a feast and were able to multiply healthily and rapidly. Fast forward to 2015 and the population of mosquitoes in the London tube are now a different species than the mosquitoes above ground.(Seriously, Check it out).
Because these mosquitoes were isolated from others of their species, they evolved differently and are now different mosquitoes altogether. Their food is different, their environmental tolerances are different and they can no longer even reliably mate with the above ground mosquitoes. These are all evolutionary changes that Darwin’s theory predicted.
Science knows it does not have all the answers. In fact, many scientists will tell you that science doesn’t have a single answer. But if we understand concepts well enough to use them, to forge ahead with knowledge, then that is enough. That is why it is critical to have criteria and tools with which to evaluate theories. When all you have to choose from are “good enough” theories, you want the best “good enough” there is.