Building on earlier ideas (presented in The Runaway Brain, 1993, and Exons, Introns and Talking Genes, 1991), Wills, an English evolutionary biologist transplanted to the Univ. of Calif., San Diego, makes a cogent case for the continued and even more rapid future evolution of our species. The counterargument: Since the advent of life-saving drugs, vaccines, clean water, and other public health measures, even the ""unfit"" survive so handily that natural selection has nothing to work on. Not true, says Wills (and most evolutionary biologists), presenting such interesting evidence in support of his position as the finding that native Tibetans have as a group lived longer than anyone anywhere else at extreme altitudes with the help of adaptive changes. (Even during pregnancy, the Tibetan fetus is able to extract more oxygen and achieve a normal birth weight more successfully than newborns of nonadapted Chinese living the same area.) Wills is at his best in presenting examples such as this, as well as in his detailed discussions of the genetic trade-offs that have led to the survival of sickle cell or cystic fibrosis genes. Via these, he reprises the paleontological literature, focusing on his pet theme: the rapid growth of the human brain and mental faculties. His opinion: Environment plays a major role in interactions with genes, which among themselves may act quite mysteriously. He also points to new evidence that the uterus itself constitutes an environment that contributes to the concordance for certain traits seen--and the difference in others--in identical twins. Ultimately, Wills forecasts a rosy future: ""smart"" pills for us to swallow as we learn more about the makeup of biochemical mind boosters; a gene pool diverse enough to meet future contingencies; life spans double what they are now. More important than this clearly optimistic vision are the cogent arguments about our evolutionary path to date and that make possible the uniquely human qualities of language, culture, and civilization.