Today is the 150th anniversary of the publishing of Charles Darwin's On the Origin of Species, a book that changed our view of biology, ourselves, and of science itself. What is interesting about it is that it was a book that was never meant to be written. Darwin was working on his "big book" on natural selection when fellow naturalist Alfred Russell Wallace independently arrived at the idea of descent with modification, that is, Darwin's theory of evolution. With his hand forced, Darwin wrote The Origin as an introduction, an abstract to the more comprehensive work he intended to produce.
The ways it changed our views of the natural world and economic life are legion, but it also changed science itself. Before Darwin, the picture of science was mechanistic. Going back to Rene Descartes, the physical world was seen as a machine whose governing principles were absolute and mathematical. In a given situation there is a completely deterministic outcome that is absolutely determinable. It was a view that Isaac Newton found deplorable as it removed God from the workings of the world, but it was a picture Newton's three laws of motion and law of universal gravitation cemented in place. Newtonian mechanics and gravitation explained so much so well that it became the touchstone, the template, the epitome of what science was to be.
Newton's laws treat objects as mass points and for any arrangements of them, give us with absolute certainty the arrangements that follow for any time in the future and allow us to determine their arrangement in the past. This view was coherent with both an atheistic materialism providing naturalistic explanations for natural phenomena and with theism and deism, providing rational principles of the sort one would expect from an all-rational Creator.
Darwin's theory in The Origins of Species, however, is different in a very important fashion.
"We can understand why a species when once lost should never reappear, even if the very same conditions of life, organic and inorganic, should recur. For though the offspring of one species might be adapted (and no doubt this has occurred in innumerable circumstances) to fill the place of another species in the economy of nature, and thus supplant it; yet the two forms -- the old and the new -- would not be identically the same; for both would almost certainly inherit different characters from their distant progenitors; and organisms already differing would vary in a different manner."For Newton, the same conditions entails the same result, not so for Darwin. This is not to say that variation follows no rules, although Darwin had no idea what they would be. This is not to say that selection follows no rules -- Darwin gives us two, natural and sexual selection. But it is to say that we can no longer think of the world as a machine, it is instead an organism. To hold a scientistic view before Darwin was to hold that the world was completely graspable, a clockwork mechanism whose principles and initial conditions simply needed unraveling. But for Darwin, it was much more complex, it was historical. For Newton, you just needed the laws and the state at any time, for Darwin, you needed the laws, the state, and a full accounting of the past. Where you are going biologically is not just a function of where you are, but where you come from. You inherit your past and you never lose it.
This was a completely different scientific stance. The world had a memory. Such a notion would appear elsewhere in science. Embryology would contain it. The recapitulation hypothesis of Serres that ontogeny recapitulates phylogeny, that as an embryo develops, it goes through stages of all of its ancestors' ancient forms is a version of this approach. Freud takes it from nature red in tooth and claw and puts in our heads neurotic and raw. People are not point masses, put in the same situations they react differently. Your mind contains its past and changes uniquely because of it.
While neither of these historically important positions held up to critical scrutiny, what we see in Darwin is an early notion of chaos, that the world may be deterministic, but in being so it is also extremely sensitive to initial conditions. Indeed, so sensitive with so many independent variables that we cannot treat it as a simple machine. This complexity may not take it beyond our comprehension, but it does make it more beautiful and awe-inspiring. It is what it is, but what it will be is a function of what it was.