Root location in random trees: A polarity property of all sampling consistent phylogenetic models except one

TL;DR

This paper demonstrates that most sampling consistent phylogenetic models, except one, inherently contain information about the root location in unrooted trees, especially as the number of taxa increases.

Contribution

It identifies a polarity property in all but one sampling consistent phylogenetic model, revealing their potential to inform root placement.

Findings

All models except one convey root location information.

The signal becomes stronger with more taxa.

Most models treat all taxa equally and are sampling consistent.

Abstract

Neutral macroevolutionary models, such as the Yule model, give rise to a probability distribution on the set of discrete rooted binary trees over a given leaf set. Such models can provide a signal as to the approximate location of the root when only the unrooted phylogenetic tree is known, and this signal becomes relatively more significant as the number of leaves grows. In this short note, we show that among models that treat all taxa equally, and are sampling consistent (i.e. the distribution on trees is not affected by taxa yet to be included), all such models, except one, convey some information as to the location of the ancestral root in an unrooted tree.