Field of Science

Larry Moran on What Evolution Is

This was written some months ago, but I just found it and I think it's worth highlighting. Larry Moran of Sandwalk posted an essay in January on the definition of evolution. The importance of definitions in science almost can't be overstated - far too much ink has been wasted on arguments between people who didn't realise that they were using a different definition.


  1. Good find - I'd missed that one. I'm not sure I agree with all of the article though. For example, Larry states that the definition of biological evolution excludes non-living things. I might like to define living things as something that undergoes biological evolution however - I think you need to be very sure of your definition of 'living' if you're going to make that exclusion. He also says "it isn't appropriate to restrict the definition of evolution to a particular mechanism even if you strongly believe that it's the only possible mechanism. That's not how you define something." Again, I have to disagree - restricting it to a particular mechanism could easily be a viable way of creating a definition.

    Then again, you can't every really be wrong with a definition. At most you can just be talking about a very different thing to what someone using the same word is talking about. Where it gets confusing is when you both then think you're talking about the same thing - as you rightly point out, this is why definitions (and, in particular, paying attention to the other person's usage of them) are so important.

  2. restricting it to a particular mechanism could easily be a viable way of creating a definition

    I strongly disagree, at least in this case. Restricting the definition to a specific mechanism a priori excludes investigation into how the process occurs. If evolution is defined as taking place through natural selection, then any generational change that might occur through other means is not evolution. This theoretically might not be a problem if we just bucked up and used the alternative term, whatever it may be. Unfortunately, people have a tendency to think that definitions are actual statements on reality, rather than initial working constructs to allow us to investigate reality. Defining evolution as occurring by natural selection might lead to people assuming that heritable change by other methods could not occur.

  3. Hmm. I take your point that restricting the definition of evolution to a particular mechanism would make for a definition that isn't terribly useful (making evolution essentially synonymous with the mechanism). I was more taking issue with the phrase "That's not how you define something." There's nothing stopping you defining things by mechanisms if you so choose, and sometimes it is appropriate, e.g. when defining natural selection.


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