Mosaic evolution in hominin phylogeny : meanings, implications, and explanations

In paleoanthropological literature, the use of the term "mosaic" (mosaic evolution, mosaic trait, mosaic species, and so on) is becoming more and more frequent. In order to promote a clarification of the use of the concept in literature, we propose here a classification in three different meanings of the notion of mosaic in human evolution: 1) morphological (inter-specific and intra-specific) instability in a certain phase of a branched phylogeny; 2) multiple trajectories and versions of the same adaptive trait in a branched phylogeny; 3) the trait itself as a complex mosaic of sub-traits with different phylogenetic stories (as is the case in language). We argue that the relevance of such mosaic patterns needs a macro-evolutionary interpretation, which takes into consideration the interaction between general selective pressures (promoting different versions of the same adaptation) and a cladogenetic approach in which speciation played a crucial role, due to ecological instability, habitat fragmentation, and geographical dispersals in human evolution.