My post the other day on the final passage in The Origin got me thinking about how amazing that book really is.Michael Ruse and some others have argued that The Origin is one long argument…one long 459pp. argument. While I think that it’s a debatable point, there’s no mistaking the brilliance and the continuity with which Darwin carried out his argument for evolution by means of natural selection.
Here’s a picture of Darwin’s notebook, the page where he first conceived of his “Tree of Life,” taken along with him on his HSS Beagle journey, and which displays the dynamics of his thought in action. Note the “I think” in the corner. Amazing! I got to see this in person once and it was a nice and humbling experience.
But what is incontestably amazing is the simplicity of Darwin’s central argument. I’ll sketch it out and then provide a more rigorous treatment. Here’s the sketch:
As many more individuals of each species are born than can possibly survive; and as, consequently, there is a frequently recurring struggle for existence, it follows that any being, if it vary however slightly in any manner profitable to itself, under the complex and sometimes varying conditions of life, will have a better chance of surviving, and thus be naturally selected. From the strong principle of inheritance, any selected variety will tend to propagate its new and modified form (1859; p.5).
Nice, huh? Note how un-teleological (purpose-driven) the process is; many, many people, evolutionists included, fail to fully get that. Here’s the more rigorous argument (where P stands for “premise” and C for “conclusion”):
P1: That there exists an appreciable amount of variation of characteristics between organisms.
P2: That there is some process by which traits pass from generation to generation (inheritance).
P3: That individual organisms reproduce many more offspring than can be sustained within any given environment.
C1: Therefore, organisms will compete for a set of limited resources (from P3).
C2: Given C1 and P1, Some variations will be more beneficial to individual organisms who possess them.
C3: Given C2, individuals possessing “profitable variations” will have a greater capacity to survive that competition for limited resources.
C4: Given C2 and C3, P1 and P3, these individual organisms will also possess a greater likelihood for producing more offspring than competitors.
C5: Given the above, individual organisms with “profitable variations” will be more likely to produce offspring and, given that there is some mechanism of inheritance, these “profitable variations” stand a better chance of being passed in to future generations. In other words, that certain variations will be naturally selected and passed to future offspring.
Now, note that Darwin had no idea about Mendelian genetics. Mendel was doing his work a few decades after the publication of The Origin and was, alas, in German, so Darwin never read it. But that’s irrelevant since the argument only needs “some” mechanism of inheritance in order to be successful. The inheritance problem bothered Darwin and bothered him more when G. Mivart (I think) leveled the “blending inheritance” problem at Darwin and his followers, but that problem was solved by Mendelian genetics (but not by Mendel himself) and the Modern Synthesis of Fisher, Haldane, and Wright (I’ll post on that later…).
But just appreciate the utter simplicity of Darwin’s argument and note that this structure works for any type of selection..for any set of organisms anywhere and anywhen, so long as those meager premises are fulfilled! And people are impressed by Einstein’s equation for its generality…