This is an ambitious, stimulating, and well-written book. Haim Ofek is concerned with the origin of the human propensity “to truck, barter, and exchange,” as Adam Smith put it. The author notes that while many animals engage in forms of nepotistic exchange (behavior that can be accounted for by the Hamilton kin-selection mechanism), humans are the only species to engage systematically in exchange with nonkin conspecifics. Rather than viewing these behaviors as cultural artifacts reflective of generations of development after the onset of the Neolithic revolution, Ofek seeks to situate their origin much earlier, in the two-million-year Pleistocene era; indeed, he views exchange, in conjunction with climactic stabilization, as a sufficient condition for—the cause, rather than a consequence of—the Neolithic revolution.