Continuities and discontinuities of variation mechanisms in on the origin of species

Abstract

Two opposing concepts of evolutionx’s rhythms have existing for several decades. There is the traditional approach initially formulated by Charles Darwin (1809–1882) and extended by Ernst Mayr’s (1904–2005) synthetic theory, which states that mechanisms of variation produce slight, regular differences that are selected continuously over time. Then there is the punctualist trend, represented by Stephen Jay Gould (1941–2002) and Niles Eldredge’s (1943) punctuated equilibrium theory, in which the fossil record mainly comprises irregular morphological leaps of unequal frequencies and amplitudes via speciations or extinctions. In order to understand the basis for this disagreement and better explain its epistemological stakes, it is helpful to look at the roots of the continuist position before molecular biology and genetics came to reinforce them. Darwin consistently bases his work on a certain idea of continuity throughout different editions of On the Origin of Species. For him, continuity appears to be both an a priori principle, justifi ed countless times by the adage of eighteenth century natural history, “nature does not take leaps”, and an induction established by close observations of living beings’ diversity. Insofar as Darwin was unaware of variation’s genetic mechanisms, he offers us a unique point of view for the study of justifi cations of the continuist concept: how did the idea of equality of variations enter into the theoretical system of the evolution of species established in 1859? The origin, characteristics and function this idea at a time when variation’s biological mechanisms were still unknown, helps clarify the current state of the punctualist versus synthetic theory discussion. This chapter establishes Darwin’s formulation of continuism in On the Origin of Species, explores the idea’s intellectual heritage, which did not suddenly appear in the progression of Darwinian thought, and concludes with an explanation of its precise function in the nascent theory of evolution.