Homology across inheritance systems

Abstract

One might think that if a character resemblance between two lineages is transmitted through different channels of inheritance -e.g., genes in one case and culture in the other -then it cannot be the result of common ancestry. The assumption that homologies cannot cross inheritance systems has framed anthropological debates regarding the phylogeny of complex cognitive and behavioural resemblances between humans and common chimpanzees, with differences in developmental acquisition taken to imply disparate phylogenetic origins (Maestripieri and Roney 2006; Marks 2003;Wrangham and Peterson 1996). In this paper we reject the assumption that any character resemblance that is culturally transmitted in one species but genetically transmitted in another closely related species is necessarily or even probably non-homologous between them.We argue that since homology relations can be preserved despite a change in developmental mechanisms ( §2), they could in principle be preserved across a change in inheritance system, even on a stringent account of what it takes to qualify as an inheritance system ( §3), so long as the trait has been continuously transmitted in a lineage. Then we turn to cultural transmission in particular, arguing that it can support phenotypic lineages and hence homology relations ( §4). We go on to describe two scenarios in which homology can cross between genetic and cultural inheritance systems (the processes of genetic and cultural assimilation) ( §5), and briefly consider whether our points carry over to developmental accounts of homology ( §6). Finally we set out the implications of this discussion for debates over the phylogeny of similar character states in humans and chimpanzees, using intergroup violence as an illustration ( §7). Homology Across Change in Developmental ResourcesReconstructing patterns of evolutionary descent has been one of the central preoccupations of biology ever since Darwin sketched the first proto-cladogram in his early notebooks. Identifying homologs is crucial to reconstructing phylogenetic relationships and delineating monophyletic taxa. On standard phylogenetic accounts of homology, a similar character state found in two different lineages is homologous just in case it was present in and inherited continuously from their common ancestor. 1 Here we adopt this 'taxic' homology concept. To 1 This paper does not take a stand on the general 'problem of homology.' Instead, we will simply stipulate that by 'homology' we mean 'taxic homology' which we define, broadly following Wiley and | P a g e 2 accommodate 'transformational homologs' (traits that correspond to, but fail to structurally resemble, one another), 'serial homologs' (e.g., digits or segments within an organism that do not share a phylogenetic history), and ancestor-descendant sequences, biologists and philosophers of science have offered non-genealogical accounts of homology grounded in mechanism and couched either in terms of shared developmental constraints or continuity of informational resources involved i...

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