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

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 (the so-called PDA model), convey some information as to the location of the ancestral root in an unrooted tree.

Highlights► We study phylogenetic models that depend just on the tree shape and the taxa present. ► One such model (Yule) favours some branches over others for rooting an unrooted tree. ► We show that just one other such model (PDA) assigns all rootings equal probability. ► We discuss the implications, since the PDA model is not biologically realistic.