What?,"" ""When?,"" and ""Why?"" are the titles Gould gives to the three short essays probing humankind's fascination with thousand-year intervals. He could probably have wrapped it all up in a single essay, but the show of erudition (one can picture Gould poring over ancient texts in Harvard libraries) will please the fans and certainly speaks to a theme that is moving more and more to center stage. ""What?"" asks why we are so fascinated with numbers, the ordering of things, and dichotomies, with Gould observing that we have moved from a belief that Christ will reign over a bountiful 1,000 years following an apocalypse to the calendric concept that at some turning of the centuries there will be a thousand-year time span that may precede an apocalypse. There really are no hard answers; Gould even states that the human brain surely did not evolve to do this kind of reckoning. ""When?"" deals with whether the 21st century begins Jan. 1, 2000, or Jan. 1, 2001. The conundrum is all the fault of a sixth-century monk who started the B.C./A.D. business but omitted a year zero. To make matters worse, Herod died in 4 B.C., so if he were contemporaneous with Jesus, revision is necessary (and accounts for Archbishop James Ussher's famous start date for the universe of 4004 B.c.). Finally, ""Why?"" returns to the issue of why mankind is obsessed with order, endowing God or nature with mathematical precision. Truth is, there is no compatibility in lunar and solar cycles, and all cultures have struggled to develop calendars to make the seasons fall where they should. All this would be a romp for Gould's wit and intellect save for a final discussion on individuals classed as autistic or retarded but who can instantaneously calculate the day of the week for a given date over centuries. Readers will be moved by Gould's personal account of the process and the person involved.