``Enigma Variations'' might be a better title to this compendium of conjectures on the where, when, and why of human origins. Seasoned science writer Shreeve, who earlier collaborated with Donald Johanson (Lucy's Child, 1989), has trekked to remote sites in Zaire and South Africa, the Middle East, Eastern Europe, Francewherever vestiges of oldest, older, and modern humans have been foundto talk to the finders, view the fossils and artifacts, and contribute his own ideas on the disputes. The result is you- are-there journalism interleaved with background history and academic discussions on the origins of language, ritual, art, and whatever else we attribute to Homo sapiens sapiensusas opposed to the Neanderthals, who only rate one sapiens in their title. Shreeve champions the idea that the Neanderthals were a separate species who neither mated with, nor were wiped out by, the Cro-Magnons or other coexisting modern types. Big-brained, probably with some form of language, art, and ritual, Neanderthals were mostly sedentary and, when times got glacially tough, dwindled down to nothingness. Not so the clans that lived and wandered nearby. ``Wandered'' is the operative word here as Shreeve argues for crosslinks of cooperation among neighboring groups that may have led to the survival of H.s.s. But questionsespecially about timingabound. What are we to make of the genetic evidence that all mankind is descended from ``mitochondrial Eve'' 200,000 years ago? The geneticists truly added fuel to a fire already kindled by arguments over dates based on radiocarbon and thermoluminescence; complex terrains where geological upheavals may have tumbled old and new bones together; inferences concerning ``higher'' mental faculties based on bone fragments or brain casts; and you have a wonderful stew a-stirring. What with the rate of new discoveries and analyses, Shreeve's text is clearly a work in progress. As such, one can pick and choose among the arguments Shreeve fully and fairly presentsor come up with a view of one's own.