Abstract

Fisher, Wright and Haldane are the main founders of population genetics, a central part of the Modern Synthesis. In addition to their scientific writings, each of them published philosophical writings presenting a certain conception of nature and evolution. However, a comparative study of these conceptions leads to a surprising result. First, Fisher, Wright and Haldane do not share the same overall conception of evolution. What is more, Wright and Haldane’s conceptions introduce elements that are foreign or opposed to Darwinism, such as the hypothesis of intentional forces, or that of a general directionality of evolution. In this sense, this study challenges the traditional narrative of unification held by some synthetists or historians. It shows that, among the synthetists, a wide variety of ideas on evolution continued to exist. First, I explain that, on the basis of an emergentist philosophy of nature, Fisher develops a philosophy of evolution consistent with Darwinism, in the sense that, for him, the main cause of evolution is natural selection. In a second step, I attempt to show that Wright’s panpsychist philosophy leads him to hypothesize that the creativity at work in evolution depends essentially on purposeful forces intrinsic to organisms, at all levels of organization in nature. In a third step, I attempt to show that, on the basis of a philosophy that is also panpsychist, Haldane hypothesizes that some laws of organization of matter give evolution a general orientation towards more complexity and mind. At the end of the chapter, I discuss the interest of taking into account the philosophy of nature and evolution defended by these biologists.