Science has a way of making people uncomfortable. Sometimes that's because it seems likely to produce agents of harm; think of nuclear weapons research. Sometimes, though, for reasons less obvious, it just feels weird. That's what happened nearly 20 years ago when scientists cloned a sheep named Dolly, and again last week when word got out that a group of biologists held a closed meeting at Harvard to talk about using laboratory chemicals to create a complete set of human DNA - a human genome. Both ideas freaked people out because they called into question the imagined boundaries between the living and the non-living, the natural and the artificial. Critics questioned what should be done with