When I was studying for my doctorate, in the late 1960s, we budding anthropologists read a book called Ideas on Human Evolution, a collection of then-recent papers in the field. With typical graduate-student arrogance, I pronounced it “too many ideas chasing too little data.” Half a century and thousands of fossil finds later, we have a far more complete—and also more puzzling—view of the human past. The ever-growing fossil record fills in one missing link in the quest for evidence of protohumans, only to expose another. Meanwhile, no single line emerges to connect these antecedents to Homo sapiens, whose origins date back about 300,000 years.

Instead, parallel and divergent lines reveal a variety of now-extinct hominids that display traits once considered distinctive to our lineage. For example, traces of little “Hobbits” found in Indonesia in 2003 show that they walked upright and made tools; less than four feet tall, with brains about a third the size of ours, they may have persisted until modern humans arrived in the area some 50,000 years ago.

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