I believe that Planet Earth and its living inhabitants are endangered by the unrestrained activities and excesses of a single species, Homo sapiens. The precarious status of Earth is a byproduct of human biology. Aldo Leopold noted that human beings are ordinary members of the biota—man has evolved by the same process that created all other forms of life and therefore has the same fundamental needs. Mankind, by happenstance and the evolutionary process, assumed a bipedal upright stance, thereby gaining distant gaze and an expanded horizon—advantageous in avoiding predators and seeking prey. Bipedal gait proved to be an efficient locomotion, which has carried man to virtually all parts of the planet. Freed from the ground, man’s upper extremities became prehensile, allowing him to physically manipulate the environment. In addition, the cranial end of man-the-organism developed into a neural center emphasizing capabilities different than those of other vertebrates—expanded cognition rather than, for example, long-range navigation or physical agility.