When it comes to the history of their discipline, paleoanthropologists align themselves with Charles Darwin. But claiming him as an intellectual ancestor is very different from testing his seminal ideas with modern techniques and data. Too often accounts of human origins owe more to Darwin's contemporary, the public intellectual Herbert Spencer. We may have outgrown his insistence on the inevitable law of human progress that once gave an unshakable direction to deep human history. But his belief that simple systems will become complex ones, largely as a matter of time, persists. Writing before Darwin's Origin was published, Spencer presented a breathtaking overview of the evolutionary process:
Whether it be in the development of the earth, in the development of the life upon its surface, the development of society, of government, of manufactures, of commerce, of language, literature, science, art, this same evolution of the simple into the complex, through a process of continuous differentiation holds throughout [Essays: Scientific, Political and Speculative (1858:3)].
John Hoffecker's Modern Humans is an erudite, meticulously researched, and well-presented account of the Spencerian process as applied to deep history. The role of information in the evolution of complex systems, of which modern humans some 60,000 years ago are an example, structures his history. Hoffecker regards modern humans and their global dispersal as a major evolutionary transition in the tradition of Maynard-Smith and Szathmáry. What underpins this transition is a shift in the way information is processed. Modern humans, he argues, have a unique capacity to translate information in the brain into complex structures; composite artifacts are one example. This capacity, he states in Chapter 1, is the paleoanthropologist's prime directive to explain.
Chapter 2 sets out the current synthesis, led by the genetic information for Homo sapiens and the framework this provides of African origins and a late global dispersal. And it is here that the Spencerian rather than Darwinian narrative comes to the fore. Modern humans are presented as having a competitive advantage when they become an invasive or colonizing species. In Chapter 3, which reviews the deeper evolutionary context, this advantage is explained as follows: “the result of intense selection pressures created by the competitive social environment (that is, reciprocal alliance network)” (p. 145). It is, however, one thing to interpret such inferred competition to account for changes in the storage, transmission, and translation of information. It is another to explain where this evolutionary impetus comes from besides the idea that complexity inevitably breeds complexity.
Chapter 4, focused on evidence for and arguments about recent African origins of modern humans, concludes that advanced syntactic language is both the source of complexity and the explanation for its continuing compilation. Hoffecker argues that, rather than a genetic change, a greater learning period, due to slower maturation rates, underpins what he regards as the “Cambrian explosion” of artifactual life after 75,000 years ago. This coalesces into a package where language and complex technology led to global dispersal supported by a framework of alliance networks. The African origins of modern humans 75,000 years ago is accounted for by the likely capacity of one subpopulation developing new and complex technologies at a faster pace than others across the continent and then, suitably equipped, aggressively expanding into new territory.
I see two problems with this account. In the first place, there is now considerable evidence, some of it only available after Modern Humans was completed, that other hominins such as Neanderthals were undergoing their own complexity splurge; cave art, display ornaments, speleofacts, burials, and composite tools emerged long before Homo sapiens began our global journey. The second is that using the historical trajectory of complexity to explain its appearance is not an explanation. For example, the selection pressure for the social brain hypothesis is not based on the possibilities that larger social networks provide to increase complexity but, instead, on the selective pressure of group defense against predators.
The book concludes with three meaty chapters on the archaeology and geography of global dispersal. Chapter 5 covers the evidence from South Asia and Australia, while Chapters 6 and 7 deal, respectively, with northern Eurasia and Beringia and America. The Pacific is omitted, and the book ends rather abruptly without a concluding chapter.
There is much to explore in this volume, and the emphasis on archaeological evidence will ensure its entry into the canon of undergraduate texts. We need more books like Hoffecker's that tackle in detail the new synthesis of genes, skulls, and tools. But we also need them to chart a new course for the evolution of humans in deep history.
