Three profiles originally written for the New Yorker -- about three Russian scientists, who fled their country to make their signal contributions to biology in the United States, have been expanded here to make a quietly exciting book. Alexander Petrunkevitch, an arachnologist, Alexis Romanoff, an embryologist, and Roman Vishniac, micro-biologist- are the three- and their portraits, amusing yet serious, also show the search for the basis of life.