DARWIN, TRANSMUTATION, AND LIVING FOSSILS BY EXAMPLE

Darwin's term "living fossils" has influenced evolutionary theory from the outset. Still today, it surfaces under many guises: taxonomic and morphological rates, punctuated equilibrium and stasis, highly conserved genes, and more. But Darwin's presentation in the Origin and other writings is a characterization by examples, not a precise definition. What epistemic support did Darwin have for his claimed examples, and how did the then-current scientific context of his different examples and his own inferences translate—or not translate—into lasting meanings, even modern ones? Here I examine these examples in context. Just prior to Darwin's publications, taxonomists including Lamarck, Geoffroy, Cuvier, Agassiz, and others disputed over "aberrant" non-European organisms, including some living fossil examples. Such disputes challenged the conventional use of traits, and which traits and not other ones, should be preferred in forming classifications, as well as their relationships to progression (or regression) and transmutation. From a modern perspective, Darwin's living fossil examples reveal part-whole relationships among traits, organisms, and phylogenetic groups. Correspondingly, Darwin attempted to select traits that informed his theories of common descent and natural selection. While some of Darwin's examples did provide direct epistemic access to the deep past, others did not. Where the fossil record was poor or absent, examples were logically underdetermined; they required inferences of ancestral states, transmutation, and descent with modification. With a richer fossil record, Darwin supported the living fossil claim for some of his examples not so much by their respective traits, but by empirical patterns of fossil distribution and abundance of inclusive "wholes"— sets of apparent related taxa with similar overall form (and classificatory status). These different chains of inferences left living fossils a confused legacy, and may have impeded attempts to derive a unified causal explanation.