The baby face with killer look

Recently discovered tooth-and-bone jewellery implies Neanderthals were as human as we are, says Alan Bilsborough

An explosion of evidence has dramatically changed the frameworks for exploring later human evolution and interpretations of the earlier hominid record. These two books reveal the extent of the conceptual shifts required to take account of this revolution.

Juan Luis Arsuaga is a Spanish palaeoanthropologist and principal researcher at Atapuerca near Burgos. Here two sites are particularly important. First, Gran Dolina provides the earliest secure evidence for hominid occupation of Europe, with Oldowan tools, animal bones and hominid remains with a date of about 800,000 years ago. The hominids have been assigned to a new species Homo antecessor , considered by Arsuaga and his associates to have both Neanderthal and modern human affinities, and to represent the common ancestor before these two lineages diverged.

The second, and younger (300,000-400,000 years ago), Sima de los Huesos ("Pit of Bones") is a pothole still only partly excavated, but so far yielding more than 4,000 human fossils from at least 28 individuals, widely regarded as proto-Neanderthals.

Arsuaga's focus is the place and significance of Neanderthals in human evolution, and his book provides a valuable counter to accounts relegating this group to a peripheral role, with our own species centre-stage. Its main thesis is that Neanderthals, although distinct outcomes of a long-established northern lineage, were as human as we are, and that similarities in behaviour, cognition and understanding far outweighed differences. The book's title refers to the recovery of pierced teeth and bones, elements of a necklace, in the Chatelperronian (Neanderthal) levels at Arcy-sur-Cure. For Arsuaga, these indicate a fondness for decoration and self-awareness by Neanderthals that is more usually attributed to the incoming Cromagnons.

Nonetheless, there were undoubted differences between the two - possibly in language capacity, certainly in appearance and the extent of artistic production. Arsuaga considers that these differences reflected Cromagnons' stronger sense of ethnic identity, which promoted both cooperation between similar groups - and therefore survival - and intolerance of those who were different.

The final disappearance of Neanderthals was a result of the combined impacts of glacial climactic severity and Cromagnon depredation, although an intriguing suggestion is that the physical differences, especially in facial form, between Neanderthals and moderns, influenced their differential survival after contact. The Neanderthal face with its enormous brow ridges was invariably seen as threatening, whereas the paedomorphic smooth-browed, flat-faced, globular-headed form of modern humans was associated in Neanderthals' minds with infants, inhibiting them from violence against Cromagnon adults. Our ancestors had no such inhibitions so far as Neanderthals, and subsequently their own kind, were concerned.

Stephen Oppenheimer also rehabilitates Neanderthals, but this is incidental to his prime purpose, which is chronicling Homo sapiens' success in peopling the globe. Out of Eden 's thrust is primarily genetic - mainly the implications of maternally inherited mitochondrial DNA population studies, but also including surveys of Y chromosome DNA. For Oppenheimer the evidence indicates that modern humans evolved in Africa; the alternative notion of regional continuity is dismissed.

Oppenheimer sees several extra-African expansions of Homo sapiens driven by climate changes, but only one that endured, with others, including a brief foray about 100,000 years ago from North Africa into the Levant ("the northern route"), dying out. According to Oppenheimer, our ancestors crossed from Ethiopia to Arabia via the Red Sea during the low sea level between about 70,000 and 80,000 years ago ("the southern route"), thence moving east to occupy south Asia and Australasia, and westwards into Europe. This contrasts with other interpretations, based on tool-kit similarities, which see Europe colonised from a second northern route expansion into the Levant later than 50,000 years ago, as well as more southerly expansion eastwards into Asia. But for Oppenheimer the monophyly indicated by mitochondrial and Y chromosome DNA precludes more than one expansion ancestral to modern humans.

Initial mitochondrial diversity in Asia soon contracted to a single line that then split into two daughter lineages, one of which, following climatic fluctuations about 50,000 years ago, expanded into Anatolia and the Levant, with a branch colonising Europe 10,000 years later. There was also expansion southwards from the Levant into North Africa (the reverse is usually posited) and movement back across the Red Sea from Arabia to the Horn. Eastwards expansion across South and Southeast Asia, predominantly along coastal routes, was rapid, reaching Australia earlier than 60,000 years ago. The earliest Arabian and Indian groups also provided the source for further movement into Central and East Asia, the former via major river systems, the latter by a combination of river and coastal routes. Fossils such as the Liujiang cranium, dated to 68,000 years ago or earlier, help calibrate parts of the picture.

Hazards also provided opportunities: the eruption of the Sunda volcano, Toba, about 75,000 years ago reduced population sizes worldwide but, by lowering sea levels, presented access to Australia. The last glacial maximum, about 18,000 years ago, also had worldwide outcomes: greater aridity and population collapse in Africa, the temporary depopulation of much of Europe and northern Asia, with the cold providing a spur to move southwards, and eastwards across the exposed Beringia land bridge into Alaska.

Oppenheimer rightly criticises the archaeologically Eurocentric notion of a "human revolution" about 50,000 years ago, and especially Richard Klein's arguments that genetically determined enhanced cognition and language capabilities underlay the archaeological transformation. Instead, he refers approvingly to Sally McBrearty and Alison Brooks' arguments for the gradual accumulation, from 300,000 years ago, of many of the indicators of "modern" behaviours in the African archaeological record. The corollary is that some anatomically archaic forms exhibited "modern" behaviours, while early sapiens groups, such as those at Skhul and Qafzeh, were still behaviourally archaic.

Much of the book is given over to detailed surveys of the genetic evidence for initial human colonisation and subsequent diversification within major continental blocs. The often-complex information is skilfully integrated with archaeological, fossil, environmental and linguistic evidence, and Oppenheimer provides an enviably clear and readable account. This book can be strongly recommended to anyone wanting an informed overview of an exciting phase in the study of modern human origins.

Alan Bilsborough is professor of anthropology and pro vice-chancellor, University of Durham.