Mosaic evolution in hominin evolution and the case of Neandertals and Modern Humans Juan Luis Arsuaga∗y1 and Mar´ıaMartin´on-Torres∗z2 1Centro UCM-ISCIII de Evoluci´ony Comportamiento Humanos. { Avd/ Monforte de Lemos, 5, Pabell´on14. 28029 Madrid, Espagne 2Centro Nacional de Investigaci´onsobre la Evoluci´onHumana (CENIEH), Paseo Sierra de Atapuerca 3, 09002 Burgos { Espagne R´esum´e Reconstructing patterns of evolution is a central issue in paleoanthropology ever since Dar- win (Arsuaga, 2010). Concerning the shape of the hominin phylogenetic tree, there are two possible geometries: basically linear (called anagenetic) or primarily branching (called clado- genetic). They correspond to two of the three classic modes of evolution defined by G.G. Simpson (1944): phyletic evolution and speciation. Concerning the tempo, speciation can be slow or fast. Supporters of Punctuated Equilibrium Theory favor a rapid speciation event followed by a long period of evolutionary stasis as predominant in evolution. On the con- trary, phyletic evolution is generally considered gradual (and called "phyletic gradualism" by punctuationists). Traditionally, neo-Darwinism tends to favor anagenesis as the main mode, and evolution is envisioned as a slow accumulation of changes in the alele frequencies of the populations. If we substitute characters for genes, and character states (traits) for aleles, the neo-Darwinian definition of evolution used in population genetics ("accumulative slow changes in the alele frequencies of the populations") would translate into "accumulative slow changes in the fre- quencies of the character states of the populations". The "accretion model" posited for the origin of the Neandertals seems to correspond to this phyletic mode of evolution (Dean et al., 1998; Hublin, 1998). The first `missing link' discovered in human paleontology was the Taung Child and resulted in an unexpected mosaic of apish and human traits. To everybody's surprise, bipedalism came earlier that encephalization in hominin evolution. As it happened in Darwin's times with Archaeopteryx, the "missing links" seem to be "mosaic links" with combinations of primitive and derived traits that are almost impossible to predict. Almost one century later, it seems that evolution of Neandertals (Arsuaga et al., 2014; 2015; Dennell et al., 2011; Martin´on-Torres et al., 2012) and modern humans (Hublin et al., 2017) has also been mosaic-like, with changes in the face and the masticatory apparatus and teeth preceding brain expansion. Does this mean that mosaic evolution is preponderant in ∗Intervenant yAuteur correspondant: [email protected] zAuteur correspondant: [email protected] sciencesconf.org:uispp2018:182385 hominin evolution? References Arsuaga, J.L., Carretero, J.M., Lorenzo, C., G´omez-Olivencia, A., Pablos, A., Rodr´ıguez, L., Garc´ıa-Gonz´alez,R., ... Bonmat´ı,A., Quam, R., Pantoja-P´erez,A., Mart´ınez,I., Aran- burum, A., Gracia-T´ellez,A., Poza-Rey, E., Sala,N., Garcia, N., Alc´azarde Velasco, A., Cuenca-Besc´os,G., Berm´udezde Castro, J.M., Carbonell, E., (2015). Postcranial mor- phology of the middle Pleistocene humans from Sima de los Huesos, Spain. PNAS 112, 11424-11529. Arsuaga, J.L., Martinez, I., Arnold, L.J., Aranburu, A., Gracia-Tellez, A., Sharp, W.D., ...Bischoff, J. (2014). Neandertal roots: Cranial and chronological evidence from Sima de los Huesos. Science 344 (6190), 1358-1363. Arsuaga, J.L. (2010). Terrestrial apes and phylogenetic trees. PNAS 107, 8910{8917 Dean D, Hublin JJ, Holloway R, Ziegler R (1998) On the phylogenetic position of the pre- Neandertal specimen from Reilingen, Germany. J Hum Evol 34:485{508. Dennell, R., Martin´on-Torres, M., Berm´udezde Castro, J.M. (2011). Hominin variability, climatic instability and population demography in Middle Pleistocene Europe. Quaternary Science Reviews 11, 1511-1524. Hublin, J.J., Ben-Ncer, A., Bailey, S.E., Freidline, S.E:, Neubauer, S., Skinner,M.M., Bergmann, I., Le Cabec A., Benazzi, S., Harvati, K., Gunz, P. (2017). New fossils from Jebel Irhoud, Morocco and the pan-African origin of Homo sapiens. Nature 546, 289-292. Hublin J-J (1998) in Neandertals and Modern Humans in Western Asia, eds Akazawa T, Aoki K, Bar-Yosef O (Plenum Press, New York), pp 295{310 in Neandertals and Modern Humans in Western Asia, eds Akazawa T, Aoki K, Bar-Yosef O (Plenum Press, New York), pp 295{310. Martin´on-Torres, M., Berm´udezde Castro, J.M., G´omez-Robles,A., Prado-Sim´on,L., Ar- suaga, J.L. (2012). Morphological description and comparison of the dental remains from Atapuerca-Sima de los Huesos site (Spain). Journal of Human Evolution 62, 7-58. Simpson, G. G. (1944) Tempo and Mode in Evolution. New York: Columbia Univ. Press. Mots-Cl´es: Speciation, mosaic evolution, anagenetic, cladogenetic, accretion, Neandertals.