Perfect Planet, Clever Species: How Unique Are We?

For many years the federal government funded the Search for Extraterrestrial Intelligence (SETI), later popularized by Carl Sagan's novel Contact and the movie starring Jodie Foster. Though in actuality SETI never did make contact with signals from an alien civilization, the search continues to this day through privately funded endeavors. How likely is it that intelligent life exists elsewhere in the universe? This is the intriguing question that has prompted William Burger's illuminating and absorbing exploration of the unusual circumstances surrounding life on earth.
Examining the critical episodes in our planet's early history and the peculiar trajectory of life on our world, Burger shows that the long odyssey of planet Earth may be utterly unique in our galaxy. For example, he describes features of the sun that are far from average. By some estimates, 95 percent of the other stars in the Milky Way galaxy are smaller, and it is unlikely that any of them could supply the energy requirements for a life-sustaining planet such as our own. Earth, as the third planet from the sun, sits within the "Goldilocks" orbit: it is in the perfect position to receive not too much heat (like Mercury and Venus) and not too little (like more distant planets of the solar system) but just the right amount to foster the development of life.
Turning to the evolution of life itself, Burger points out a host of amazing accidents (for example, the extinction of dinosaurs and the proliferation of flowering plants) that make the steps along the way to Homo sapiens seem like very rare events indeed. He also calls attention to the curious fact that the early hominid brain tripled in size over the relatively short time period leading to the appearance of modern human beings. Finally, he notes aspects of humanity's cultural evolution that seem unlikely to have been duplicated anywhere else.
Burger's enlightening evaluation of evolutionary and cosmic history, full of fascinating details, shows that the human achievement may be unique in our galaxy.