Species, genes, and the tree of life

A common view is that species occupy a unique position on the Tree of Life. Evaluating this claim this requires an understanding of what the Tree of Life represents. The Tree represents history, but there are a least three biological levels that are often said to have genealogies: species, organisms, and genes. Here I focus on defending the plausibility of a gene-based account of the Tree. This leads to an account of species that are determined by gene genealogies. On this view, an exclusive group is a group of organisms that forms a clade for a higher proportion of the genome than any conflicting clade. Taxa occupy a unique position in what can be called the 'primary concordance tree'. But each gene has its own historical 'tree of life'. I conclude by arguing that both organismal pedigrees with their corresponding Tree as well as gene genealogies and their trees are objectively real and play important, but different, roles in biological practice.