Many generations of thinkers, both religious and scientific, have been led astray by anthropic assumptions, while others were simply led astray by ignorance. In the absence of dogma and data, history tells us that it's prudent to be guided by the notion that we are not special, which is generally known as the Copernican principle, named for the Polish astronomer Nicholas Copernicus who, in the mid 1500s, put the Sun back in the middle of our solar system where it belongs. In spite of a third century B.C. account of a sun-centered universe proposed by the Greek philosopher Aristarchus, the Earth-centered universe was by far the most popular view for most of the last 2000 years. Codified by the teachings of Aristotle and Ptolemy, and by the preachings of the Roman Catholic Church, people generally accepted Earth as the center of all motion. It was self-evident: the universe not only looked that way, but God surely made it so. The sixteenth century Italian monk Giordano Bruno suggested publicly that an infinite universe was filled with planets that harbor life. For these thoughts he was burned upside down and naked at the stake. Fortunately, today we live in somewhat more tolerant times.
While there is no guarantee that the Copernican principle will guide us correctly for all scientific discoveries to come, it has humbled our egos with the realization that not only is Earth not in the center of the solar system, but the solar system is not in the center of the Milky Way galaxy, and the Milky Way galaxy is not in the center of the universe. And in case you are one of those people who thinks that the edge may be a special place, then we are not at the edge of anything either.
A wise contemporary posture would be to assume that life on Earth is not immune to the Copernican principle. If so, then how can the appearance or the chemistry of life on Earth provide clues to what life might be like elsewhere in the universe?
I do not know whether biologists walk around every day awestruck by the diversity of life. I certainly do. On this single planet called Earth, there co-exist (among countless other life forms), algae, beetles, sponges, jellyfish, snakes, condors, and giant sequoias. Imagine these seven living organisms lined up next to each other in size-place. If you didn't know better, you would be hard-pressed to believe that they all came from the same universe, much less the same planet. Try describing a snake to somebody who has never seen one: "You gotta believe me. There is this animal on Earth that 1) can stalk its prey with infrared detectors, 2) swallows whole live animals up to five times bigger than its head, 3) has no arms or legs or any other appendage, yet 4) can slide along level ground at a speed of two feet per second!"