Summary
This book (as the title implies) is interested in the emergence of species, and now that we are talking about it, what are species to begin with? At the time, there were many very experienced naturalists who would disagree on whether a certain plant or animal belonged in species A as a variety or actually should be considered a distinct species. These disagreements arose due to the fact that no one had a clear theory as to how these differences arose and up to then we used internal and external structure to define species. If these structures diverged enough, we would separate them into species. They also used the concept of whether entity A could potentially breed with entity B. If not, then the two entities must not be in the same species. There were other methods used, but these two should suffice to show how difficulties in definition might arise. For example, the internal and external structure of sexed organisms may very greatly as in humans, but we obviously must be the same species, right?….. Actually, that might explain some things. As for mating, this brings its own difficulties (I’m on a roll), but strictly speaking, you can have two different species reproduce, like a grizzly bear and polar bear, and this happens quite often in the plant kingdom. On the other hand, you have many instances of creatures in the same species category that can’t reproduce inside their own species. Think Mastiff and Chihuahua. So these principles are by no means black and white. The prevalent view at the time was the belief that each species was created individually, with this view the categorization of species should be much more straight-forward than it is, but Darwin had other ideas. Using pigeons, due to their availability and the long history they have of human selection, he built an argument. He stated that if we had found the various varieties of pigeons in the wild, we would without a doubt classify them as different species. We only refrain from doing so because we happen to know in this case that all the varieties descended from rock pigeons. What if this same concept applied to the whole animal kingdom? What if instead of individually created species there was a single progenitor which has given rise to the magnificent variety we observe today? How far might these accumulated minute changes take us?
Thoughts
The first half of this book was fantastic, highly readable and enjoyable. The second half felt a little dry but had some really interesting parts as well, specifically thinking of the section on the dispersal of species across continents. Overall, I was really impressed with just how fully thought out this theory was. I expected it to be more of a rough scaffolding, but the number of examples and details he sketched out was incredible. I am not quite sure how it was possible for someone to have such a breadth of knowledge before the internet. This also cleared up a lot of misconceptions I had about the theory and answered many of the questions I had. Beyond that it also shed light on various phenomenon that had puzzled me. One of the most interesting topics to me was that of invasive species. Darwin theorized that when one species was allowed to have a large range it would become more “highly developed” due to a high amount of competition. On the other hand, species that were largely secluded and only covered a small range would be less developed. As a result if any of the highly developed species were introduced to the secluded group, they would almost always dominate the lesser developed species and replace them in the ecosystem. As a general rule of thumb this has been bourn out, especially on islands. You could also loosely make the argument (as Jared Diamond has) that this principle applies to people as well. I also have to mention that Mammoth cave was explicitly called out in this book. Darwin was making the observation that cave animals presented another difficulty with the idea of separate creation. The animals in caves are often blind, but curiously they are also endemic. With the idea that species were created, one would expect that there would be a whole class of cave animals that are especially designed to live in caves, but instead what we find are local creatures that have adapted to cave life. So in Kentucky we have Kentucky cave fish, whereas in European caves you would have European cave fish. These fish will be found to be more closely related to fish near them, than to fish in other caves. This of course, suggests a slow migration instead of a specific creation. In conclusion, this was a highly impressive work for a very unintuitive theory. I am reminded of Conway’s game of life, or Boids, often complexity can be generated by some simple rules and reverse engineering those “rules” are often very unintuitive.
People/Charles Darwin