Today the only place to see woolly mammoths and people side-by-side is on The Flintstones or in the movies. But researchers are on the verge of piecing together complete genomes of long-dead species such as Neandertals and mammoths. (See a brief overview of human genetics.) So now the big question is, Will we soon be able to bring such extinct species back to life? Researchers are divided over how they might try to do this and whether it's even feasible. (Related: "Woolly Mammoth Resurrection, 'Jurassic Park' Planned [April 8, 2005].) At the core of this issue is DNA, which encodes...