Hybrid evolution and horizontal gene transfer (HGT) are processes whereevolutionary relationships may more accurately be described by a reticulatednetwork than by a tree. In such a network, there will often be several pathsbetween any two extant species, reflecting the possible pathways that geneticmaterial may have been passed down from a common ancestor to these species.These paths will typically have different lengths but an `average distance' canstill be calculated between any two taxa. In this article, we ask whether thisaverage distance is able to distinguish reticulate evolution from puretree-like evolution. We consider two types of reticulation networks:hybridization networks and HGT networks. For the former, we establish a generalresult which shows that average distances between extant taxa can appeartree-like, but only under a single hybridization event near the root; in allother cases, the two forms of evolution can be distinguished by averagedistances. For HGT networks, we demonstrate some analogous but more intricateresults.
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