Similarities as Evidence for Common Ancestry -- A Likelihood Epistemology

TL;DR

This paper uses likelihood theory and mathematical models of evolutionary processes to evaluate when similarities between species serve as evidence for common ancestry, clarifying Darwin's claims.

Contribution

It introduces a likelihood-based framework to assess the evidential value of similarities for common ancestry, considering different evolutionary processes.

Findings

Likelihood analysis clarifies when similarities support common ancestry.

Mathematical models differentiate between types of evolutionary processes.

Results apply to both Darwin's theory and modern evolutionary biology.

Abstract

Darwin claims in the {\em Origin} that similarity is evidence for common ancestry, but that adaptive similarities are "almost valueless" as evidence. This claim seems reasonable for some adaptive similarities but not for others. Here we clarify and evaluate these and related matters by using the law of likelihood as an analytic tool and by considering mathematical models of three evolutionary processes -- directional selection, stabilizing selection, and drift. Our results apply both to Darwin's theory of evolution and to modern evolutionary biology.