Here Be Dragons:

The discovery of life on other planets would be perhaps the most momentous revelation in human history, more disorienting and more profound than either the Copernican or Darwinian revolutions, which knocked the earth from the center of the universe and humankind from its position of lofty self-regard. In Here Be Dragons, astronomer David Koerner and neurobiologist Simon LeVay offer a scientifically compelling and colorful account of the search for life beyond Earth.
The authors survey the work of biologists, cosmologists, computer theorists, NASA engineers, SETI researchers, roboticists, and UFO enthusiasts and debunkers as they attempt to answer the greatest remaining question facing humankind: Are we alone? From their "safe haven of skepticism" the authors venture into the "rough seas of speculation," where theory and evidence run the gamut from hard science to hocus pocus. Arguing that the universe is spectacularly suited for the evolution of living creatures, Koerner and LeVay give us ringside seats at the great debates of Big Science. The contenitous arguments about what really happens in evolution, the acrimonious UFO controversy, and the debate over intelligence versus artificial intelligence shed new light on the wildly divergent claims about the universe and life's place in it. The authors argue that while no direct evidence of extraterrestrial life yet exists, habitats and chemical building blocks for life abound in the universe. A wealth of new astronomical techniques and space missions may provide this evidence early in the next century.
Lucidly written and scientifically rigorous, Here Be Dragons presents everything we know thus far about the emergence of intelligent life here on earth and, perhaps, beyond.