Darwin’s One Long Argument

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…

About these ads

1 Comment

Filed under Biology, Darwin, Science

One response to “Darwin’s One Long Argument

  1. Great post! Really enjoyed the explication of the logical argument. It has gotten me thinking about several things I have considered at varying times. The book itself I find fascinating and I haven’t read it in almost ten years; this really makes me want to pick it up again. I was glad that Easton Press included it in their series “100 Greatest Books Ever Written”, especially since the series concentrates on classical literature.

    One thing that has always intrigued me is how quickly the topic of Darwin becomes taboo when we logically apply these premises and conclusions to the animal species known as homo sapiens. What I find interesting about these particular creatures is their adaptation to advanced forms of technology, which I have often wondered what influence it has on stretching but not breaking the long Darwin argument. For instance, these homo sapiens follow premise 3 like any other animal (That individual organisms reproduce many more offspring than can be sustained within any given environment) but their technology allows them to change the natural parameter of a biosphere or planet to extend the capacity of a physical biological area as they continue to overpopulate (though this doesn’t make premise 3 false in any means to us, it is just we have more power of manipulation, if we all just started living on self-sufficient space ships and sailing around in fleets as nomads it opens some interesting questions about environment and life and selection). However, no other species we have studied has the same power, at least to the same degree I should say, on Earth anyway. How, if at all, does this affect the conclusions of the long argument?

    For example, conclusion 2 becomes a socially awkward, politically charged conversation if you take the logic of the argument (Given C1 and P1, Some variations will be more beneficial to individual organisms who possess them) and apply it to ourselves. Certainly humans have many variations of characteristics (premise 1), and we definitely compete for limited resources as we continue to populate (conclusion 1), so the premise and lemma inferring conclusion 2 seems to logically apply to ourselves, which can be quite uncomfortable. I fear the negative side of conclusion 2 is an incalculable sum of justification for bigotry. But it can be a positive. Consider the evolution of lactose digestion, where homo sapiens continue to evolve in a manner reflecting our adult consumption of dairy products that most of our ancestors would not be able to properly absorb (though it may surprise people that most of the human race continues to have some cellular level of resistance in this manner) or the Tibetans whom in the last 2,000 to 3,000 years are now capable of more efficiently breathing Himalayan air in comparison to any other group of people in the world.

    But I wonder, is society mature and ready enough to have a serious non-political, non-religious conversation about ourselves and our relationship to conclusion 2? Will new scientific fields such as genetic engineers suffer the same fate as the climate scientists?

    One of the things I find interesting, however, is how does economics and medical science advances alter, if at all, conclusion 2 or conclusion 4? I was born with a genetic mutation known as Axenfeld-Riegers syndrome, with the consequence that if one of the congenital genetic issues I inherited was left untreated by medical science, I was told at 16 I should be dead by 30, at the latest (I’m 29 so I am thinking about that a lot more these days!). Is it a plus or minus that if I have children and people like me have children we pass on these sorts of genetic problems with greater probability? Over the generations what net effect is this having on our physical health? It is not ideal but can morally be done with scientific man stretching the nature of biological selection?

    And what about genetic engineering? Francis Bacon used to say that Nature was our mistress, that science was there to enslave her (what can I say its Bacon and they did not have a lot of alternative porn back then). Do we master our very nature to the point where we create artificial selection? I always have wondered what this does to the naturalism/anti-naturalism debate. Say you control all the keys to life. You can manipulate through genetics, moral character, virtue and vice, you can control appearance, intelligence, whatever you desire. Would not you need some fundamental normative set of choices to craft human nature? How could you rely on the naturalistic evidence alone? Naturalism tells you how to do something, it describes processes, but in itself it does not hold they keys to making the decisions about which process or possibility to create beyond questions of simplicity, efficiency, correlation, or procedure. How could you ever justify making the normative choices of creating the entire genetic code of a species if you had the power to do so? How does natural history alone tell you the genetic engineer what you ought to do?

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s