Abstract :
This paper describes a pattern of explanation prevalent in the biological sciences that I
call a ‘lineage explanation’. The aim of these explanations is to make plausible certain
trajectories of change through phenotypic space. They do this by laying out a series
of stages, where each stage shows how some mechanism worked, and the differences
between each adjacent stage demonstrates how one mechanism, through minor modifications,
could be changed into another. These explanations are important, for though
it is widely accepted that there is an ‘incremental constraint’ on evolutionary change,
in an important class of cases it is difficult to see how to satisfy this constraint. I show
that lineage explanations answer important questions about evolutionary change, but
do so by demonstrating differences between individuals rather than invoking population
processes, such as natural selection.
