The common ancestor of modern humans and the great apes is estimated to have lived between 5 and 8 Myrs ago, but the earliest evidence in the human, or hominid, fossil record is Ardipithecus ramidus, from a 4.5 Myr Ethiopian site. This genus was succeeded by Australopithecus, within which four species are presently recognised. All combine a relatively primitive postcranial skeleton, a dentition with expanded chewing teeth and a small brain. The most primitive species in our own genus, Homo habilis (...) and Homo rudolfensis, are little advanced over the australopithecines and with hindsight their inclusion in Homo may not be appropriate. The first species to share a substantial number of features with later Homo is Homo ergaster, or ‘early African Homo erectus’, which appears in the fossil record around 2.0 Myr. Outside Africa, fossil hominids appear as Homo erectus‐like hominids, in mainland Asia and in Indonesia close to 2 Myr ago; the earliest good evidence of ‘archaic Homo’ in Europe is dated at between 600–700 Kyr before the present. Anatomically modern human, or Homo sapiens, fossils are seen first in the fossil record in Africa around 150 Kyr ago. Taken together with molecular evidence on the extent of DNA variation, this suggests that the transition from ‘archiac’ to ‘modern’ Homo may have taken place in Africa. (shrink)

The considerable variation in shape, size, structure and properties of the enamel cap covering mammalian teeth is a topic of great evolutionary interest. No existing theories explain how such variations might be fit for the purpose of breaking food particles down. Borrowing from engineering materials science, we use principles of fracture and deformation of solids to provide a quantitative account of how mammalian enamel may be adapted to diet. Particular attention is paid to mammals that feed on ‘hard objects’ such (...) as seeds and dry fruits, the outer casings of which appear to have evolved structures with properties similar to those of enamel. These foods are important in the diets of some primates, and have been heavily implicated as a key factor in the evolutionary history of the hominin clade. As a tissue with intrinsic weakness yet exceptional durability, enamel could be especially useful as a dietary indicator for extinct taxa. BioEssays 30:374–385, 2008. © 2008 Wiley Periodicals, Inc. (shrink)

These three books consider the nature and evolutionary context of the individual and collective behavior of modern humans. Moffett’s The Human Swarm and Christakis’ Blue­print focus on the “big picture.” What, if anything, is distinctive about the ways groups of modern humans behave? What do modern human societies have in common that distin­guishes them from aggregations of non-human organisms? Wrangham’s The Goodness Par­adox focuses more narrowly on aggression, and the enigma that modern humans seem to be individually relatively docile, but (...) collectively capable of planning and executing highly aggressive activities. I was intrigued and educated by all three books. (shrink)