No technical barrier prevents selection for eye color, hair color, or - as we learn more about their predisposing genetic factors - height, IQ, or gregariousness. Parents willing and able to pay $25,000 a year for their kids’ K-12 education will try genetic enhancement, too, if it’s shown to be risk-free.

Terrific! Selecting for smarter kids isn’t any sleazier than springing for SAT prep courses, whose effects are superficial and temporary - although bringing the bottom up using high performers’ “template alleles” will be easier than pushing the top higher. Bailey, who has never met an enhancement he didn’t like, paints a blithely benign portrait of our genetically enhanced future. But ask Microsoft what happens when you change one line of a 10 million-line code. Pleiotropy - multiple effects of a single gene - can lead to unanticipated consequences. And engineering people with heritable enhancements - say, incredible night vision plus nocturnal alertness - will differentiate them behaviorally and could lead to sub speciation.

More likely, though, parents chasing celebrity phenotypes will foster conformist convergence. Sameness breeds fierce micro-competition, like wrangling over a corner office. Memo from Darwin: Selection occurs not between but within species. Load all those height genes into kids’ genomes; there will always be a bottom third percentile. Some poor kid is still going to get called a shrimp.

Meanwhile, the hot thing in engineering is nanotechnology: learning to assemble tiny wheels, gears, propellers, grasping appendages, motors, computers - the stuff big machines use - atom by atom. Nanotech futurist Robert Freitas has designed spheres about 3,000 atoms across, with onboard computers and rotors and oxygen-carrying capacities 100,000 times that of red blood cells. Replace 10% of your blood supply with these “respirocytes” and you can sit at the bottom of a pool for hours. (Think “internalized scuba.”) Respirocytes’ practical realization is 10 or 20 years off, but soon thereafter, writes Kurzweil, you’ll have remotely programmable nanobots whistling through your blood vessels, scraping off plaque or plunging little carbon-nanotube arms into cells to suck out gunk, kill viruses, or repair mutated DNA. With nanobots monitoring every critical neural connection’s involvement in a thought or emotion or experience, you’ll be able to back up your brain - or even try on someone else’s - by plugging into a virtual-reality jack. The brain bots feed your synapses the appropriate electrical signals and you’re off and running, without necessarily moving.

If nanotechnology gets traction, all bets are off, because whoever’s packing those brain bots will be infinitely more intelligent than mortal meat puppets like me.

Key to Kurzweil’s vision is the idea that Moore’s law persists long-term and cuts across all technological fields. The super - imposition of exponential curves spells not mere acceleration of technical advancement but an increasing rate of acceleration. If that much of Kurz weil’s thesis holds up, even gross underperformance will delay by just a few years the culmination he labels the Singularity. Kurzweil’s prophesied apotheosis will feature, for starters, “actuarial escape velocity” - life expectancies growing by more than one year annually. Hang in there for 30 years and immortality is at hand. And so is the reverse engineering of the human brain, its biological circuitry usurped by far more efficient nanobotics.

I wish I could share Kurzweil’s sanguine view that, after such a Promethean leap, the foot landing on the far side will be a human one. The Tin Woodsman retained his humanity by recalling his emotional core - “If I only had a heart,” he croons in the movie. In finally triumphing over our biological constraints, we will effectively create God, or gods. I hope our sleek semiconducting successors like pets, because, while the mammalian herding instinct ensures that many of us will go along for the ride, charac teristic human obstinacy ensures that many will not.

Bailey, ever the libertarian, says that’s your choice. Fukuyama says some choices should be curtailed. Kurzweil says it’s all inevitable, anyway. I say, can we at least draw a couple of pink lines someplace? We’re all Silicon Woodsmen now. And I like this movie, but it’s speeding up and the action’s getting a little jumpy.

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