Early Homo skeletal material is loosely associated with two successive tool traditions, the Oldowan and the Acheulean. H. erectus spread out of Africa and into island southeast Asia, tolerating temperate climates and apparently crossing deep water, apparently some 1.7 mya (Rightmire et al., 2006). Some authorities emphasize the expedient simplicity of the Oldowan and early Acheulean industries. De la Torre and colleagues (2003, 2008) argue that a rather sophisticated appreciation of the properties of stone, and a fairly sophisticated approach to knapping, characterized these two industries. Sharon (2009) presents evidence that Acheulean makers of large biface tools had efficient and culturally variable techniques for producing these signature artifacts. A recently published Acheulean campsite dating to 750 kya seems to have been fairly complex. It contained remains suggesting that H. erectus could exploit a wide variety of plant and animal resources, including fish and acorns, and that they controlled fire (Alperson-Afil et al., 2009). Evidence for still-earlier use of fire is controversial (Wrangham, 2009). Interestingly, reports on living individuals with primary microcephaly (small brains but without organizational disruptions) indicate that they suffer only mild to moderate mental retardation (Cox et al., 2006). Perhaps these brains are a clue to the cognitive capabilities of H. erectus. H. erectus’s brain architecture and behavior might have been rather modern in many respects. Donald (1991) suggests that H. erectus had advanced abilities to imitate motor patterns but still lacked speech. He reviews 19th-century data on deaf mutes as evidence that alinguistic people would be capable of imitating many if not most modern skills except ones directly dependent on language. Thus, culture-led gene–culture coevolution could have been an active process in this period. After 1 mya, the 100-ky cycle came to dominate the low-frequency component of the climate record. Early in this period, larger-brained hominins, often lumped into the taxon H. heidelbergensis, evolved in Africa and western Eurasia (Rightmire, 2009a). Thus, there are hints, but at this point only bare hints, that changes in climate variation were increasing selection in favor of more sophisticated culture capacities. Some progress has been made on the representation of tool use in the brain (Peeters et al., 2009). Many genes associated with the ability to make and use tools probably evolved during this long period.
Since the sequencing of the chimpanzee genome, a considerable amount of effort has gone into searching for the differences between the two species (Kehrer-Sawatzki and Cooper, 2007; Portin, 2007, 2008; Varki and Nelson, 2007). Many candidates for genes that have come under selection have turned up in these comparisons. Some of the apparently most interesting genes, such as copy number in the gene MGC8902, have unknown function. The large OR family of genes (~1,000–1,400 loci) involved in odor perception has a very high percentage of nonfunctional