a response on darwin's behalf

Just like the paradigm shift that resulted from Isaac Newton’s development of the law of universal gravitation, there was a similar paradigm shift in the field of biology that stemmed from Charles Darwin’s radical theory of evolution. Pre-Darwin, biologists believed that all organisms present on Earth were created by an omniscient “creator” or God. In the earth 19th century, Lamarck developed his theory of transmutation which stated that organisms were not fixed but rather changed over time to better suit the needs of the environment. This challenged the idea of a fixity of species created by an omniscient being — why would a God create animals that were not perfect, and thus needed to change over time. Darwin noticed that animals seemed well-adapted to their surroundings and that offspring seemed to resemble their parents, and theorized that, over time, the most useful traits were passed down through a process he called natural selection. A real critique of Newton’s theory by his contemporary Gottfried Wilhelm Leibniz was that Newton did not provide a causal explanation for his theory of planetary movement. Similarly, we can imagine a Leibnizian critique of Darwin’s theory: “Without telling us the underlying causal mechanisms for both variation and inheritance, your theory of evolution is at best incomplete and is certainly not a full-fledged scientific theory.” To Leibniz, a causal mechanism was missing. However, I will argue that while Darwin and Newton’s theories are analogous in that both are missing causal explanations for their theories, the kind of critique I have mentioned is invalid for both Darwin and Newton and thus, their theories can be called “scientific.”

First, we must discuss what both Newton and Darwin “give us” in their theories and what they do not. This will help us understand what kind of “causal mechanism” Leibniz and similar critiques are looking for. In Newton’s Principia Mathematica, he sought to explain the reasons planets move the way they do, as approximated by Kepler’s Laws. He theorized that a force called gravity pulled bodies towards each other at a force proportional to the square of their distances. However, Newton did not give us any explanation for why gravity exists, and how such a force could have come to be. Similarly, in Darwin’s Origin of Species, Darwin sought to explain the reasons that animals seemed well-adapted to their environments and why children resemble their parents. So, he theorized that organisms evolve through the mechanism of natural selection with the help of variations within a population. However, Darwin does not give an explanation for why variation exists or a biological mechanism for how inheritance works. We can see how these discoveries are analogous: neither of them provided explanations for the mechanism they describe, but they both do provide us with mechanisms that explain certain phenomena. Newton did not provide a causal mechanism of gravity but provided a mechanism for planetary movement. Darwin did not provide a causal mechanism for inheritance or natural selection, but did explain why offspring resemble their parents and why animals seem well-adapted to their environment. In the case of Newton, a causal mechanism would be similar to our current understanding of Einstein’s theory of relativity, which explains how the bending of spacetime creates the effect that gravity produces. Darwin’s theory of evolution could have been supported by the causal explanation that genes are passed down through DNA and gametes. I argue that any causal explanation Darwin or Newton could have provided would not have been scientific.

I hold that a scientific theory must be testable for it to be called scientific. While this is in no way an exhaustive definition, if we can show that the causal mechanism would not have cohered with this criterion, we have proved that the theory would not have been scientific. I also hold that, for a theory to be testable, it must be both practically and pragmatically testable. Practically testable theories are those that can be physically tested with the equipment available to the tester at the time. For example, Einstein’s theory of relativity would not have been practically testable in Newton’s time because he did not have access to advanced space telescopes which would have revealed phenomena like gravitational lensing. Pragmatically testable theories are those that can be tested with available technology, but are too radical in the context of existing scientific beliefs. That is, the theory goes against the existing paradigm in such a way that the scientific framework to test the theory is completely lacking.

Any causal explanation that Newton provided for his theory of gravitation would have likely been practically untestable. The prevailing idea at the time for the cause of planetary movement was the existence of tiny particles that “pushed” bodies (like planets) around. In order to test something like this, Newton would have needed advanced experimental devices, such as our advanced satellite cameras, telescopes, space expeditions, and advances in precise microscopes, which just were not available in his time. Limited by the technology available at the time, any kind of hypothesis that Newton could make would not be grounded in any kind of empirical evidence, and thus, can be labeled as unscientific.

Similarly, any causal explanation for natural selection would have likely been pragmatically untestable. We need to take into account the “scientific stock” of information that was available to Darwin at the time. There was absolutely no framework for any kind of causal explanation: the field of genetics was not developed until the mid-19th century and molecular biology was not understood until the 1930s and 40s. Without a genetic framework, Darwin had no means to explain how traits were passed from one generation to the next which clearly inhibits his ability to provide any comprehensive causal explanation. Any explanation would also have to leave out molecular biology, giving Darwin an extremely small set of possible causal explanations to work off of. Darwin’s hypothetical causal explanation would also not be based on observed phenomena: the observed phenomena at the time was biodiversity, variation, and adaptation. These were explained by his heritability and natural selection. If he were to provide a further explanation, like a mechanism for inheritance, this would not be in terms of phenomena observed and empirical evidence because a framework required to observe the molecular processes underlying genetics did not exist. Clearly, Darwin could not provide a pragmatically testable causal explanation, and thus, any explanation would have been unscientific.

A possible counterexample is that Darwin and Newton could have provided some sort of causal explanation that was testable. For example, Darwin could have said that there were particles that transmitted traits from parent to offspring, and it could have been testable by looking at the development of a fetus through a microscope. While this is conceivable, it still would likely not have been possible to observe these phenomena when we look at the constraints of the time: lack available technology, the absence of the necessary scientific knowledge, and the prevailing paradigm of a fixity of species and special creation.