What Can Life on Earth Tell Us About Life in the Universe?

Abstract

We review the most fundamental features common to all terrestrial life. We argue that the ubiquity of these features makes them the best candidates for being features of extraterrestrial life. Other frequently espoused candidates are less secure because they are based on subjective notions of universal fitness, not on features common to all terrestrial life. For example, major transitions in the evolutionary pathway that led to Homo sapiens are sometimes considered to be fundamental transitions in the evolution of all life. However, these "major transitions" are largely arbitrary because a series of different major transitions can be identified along the evolutionary pathway to any extant species.