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Volume 5 (2013) Current Issue

Can fitness differences be a cause of evolution?

Grant Ramsey

The causal status of fitness and natural selection is increasingly called into doubt in the philosophical literature. For example, Elliott Sober argues that the fitness of individual organisms is holistic; i.e., it is dependent osn causally independent factors like census size. Others have argued that fitness differences cannot properly be causes of evolutionary change. In this paper I directly challenge the holistic conclusion, and thereby shed light on the debates over the causal status of fitness. I show that the causalists and statisticalists are—to a large degree—arguing past each other. There is a plurality of fitness concepts; some are legitimately causal, while others seem to be based, at least in part, on purely statistical parameters. But such facts say nothing about whether fitness in general is causal or statistical.

Phylogeny as population history

Joel D. Velasco

The construction and use of phylogenetic trees is central to modern systematics. But it is unclear exactly what phylogenies and phylogenetic trees represent. They are sometimes said to represent genealogical relationships between taxa, between species, or simply between “groups of organisms.” But these are incompatible representational claims. This paper focuses on how trees are used to make inferences and then argues that this focus requires that phylogenies represent the histories of populations.

Developmental causation and the problem of homology

David A. Baum

While it is generally agreed that the concept of homology refers to individuated traits that have been inherited from common ancestry, we still lack an adequate account of trait individuation or inheritance. Here I propose that we utilize a counterfactual criterion of causation to link each trait with a developmental-causal (DC) gene. A DC gene is made up of the genetic information (which might or might not be physically contiguous in the genome) that is needed for the production of the organismic attributes that comprise the trait. I argue that individuated traits—phenes—correspond to organismic features that are caused by DC genes. Using such an approach, we can define a DC map, which shows the relations between each pair of phenes and provides a succinct summary of genotype-phenotype relationships and phenotypic complexity. Phenes in parents and offspring are judged to be homologous if their DC genes are composed of orthologous genetic factors. When comparing more distantly related organisms, traits are homologous when linked by a chain of parent-offspring homologs along the path of ancestry that links the two organisms. There are three possible ways to deal with the potential for multiple equivalent DC genes: maximal, minimal, and consensus homology. Whereas maximal homology has limited utility, the other two approaches have value and can help to guide research at the intersection of evolution and development.