The paradigmatic shifts in the history of biology and the problem of units of selection

When approached from a Kuhnian perspective, it becomes evident that, just as in the philosophy of physics, normal science, discoveries, crises, and revolutions also play crucial roles in the history of biology. Until Darwin, the fixed typological concept of species—believed to be created by God and without transitional forms—prevailed. However, with Darwin, this notion was replaced by a dynamic understanding of speciation, where species are not fixed but instead originate from a single common ancestor and are related to one another through natural selection. It can be argued that Darwin's theory of evolution triggered a revolution comparable to the Copernican Revolution and that there was a paradigm shift in the history of biology from an Aristotelian paradigm to a Darwinian one. Since Darwin's theory of evolution, no further paradigm shifts have occurred. Fisher, Haldane, and Wright significantly contributed to the maturation of the theory, making evolution quantitatively measurable. Later, the works of Dobzhansky, Huxley, and Simpson were added to these developments. While Fisher, Haldane, and Wright's studies were concerned with microevolution, the works of Dobzhansky, Huxley, and Simpson focused on macroevolution. The integration of microevolution and macroevolution ensured the coherence of the modern synthesis. Although there was conceptual unity regarding the synthesis, disagreements arose over the question of the unit of selection. While Dawkins and Williams argued that genes were the sole unit of selection, Sober and Wilson opposed this view. They suggested that not only genes but also organisms and groups could serve as units of selection. In response to Sober and Wilson's claim, this study aims to demonstrate that individual holobionts function as units of selection. Key Words: Paradigm, revolution, history of biology, evolution, units of selection, holobiont.