Question

Is complex animal life common in the universe or are we the only ones at this level of existence?

Although we have not yet discovered any other life forms of any kind anywhere else in the universe, some theories such as those proposed by Carl Sagan and Frank Drake predict that complex animal life should be prevalent in our universe. On the other hand, a recent book entitled Rare Earth, by Robert Ward and Donald Brownlee, seems to suggest that life, both complex and simple, is rare. For a good summary of the requirements for planet habitability (the measure of complex life), please refer to the response to above question: "What makes Earth so unique in the Solar System." For more details about the theory that only microbial life is common, check out this non-NASA site: http://www.seti.org/science/rare_earth.html One needs to remember, size is not always a measure of complexity. A microbe is in some ways far more advanced and complex than any large mammal such as a human or a lion. For example, most bacteria are capable of what is called “horizontal gene transfer,” or, the passing of genes within a generation not involving reproduction. The only way mammals have of sharing genes is through “vertical gene transfer,” or passing on genes into the next generation through reproduction. The sharing of genetic information within a generation increases population diversity and survival rate without having to wait for the next generation. Wouldn’t it be great if you could just, give a person who has cystic fibrosis (a disease caused by a malfunction of a single gene) a copy of your functional CF gene? Well, bacteria can do that with their genes. As Bruce Jakosky, from the NAI’s University of Colorado Center states, "Finding even bacteria on another planet would tell us that life has had an origin somewhere that was independent of life on Earth, that life could arise more than once. My own view is similar to that of many other scientists--that the occurrence of even a single other example of a life-bearing planet would be as significant philosophically as the discovery of intelligent beings elsewhere in the galaxy. It would mean that life is not unique to the Earth…. Whether intelligent species could exist then would depend only on the thread of evolution that occurred on each planet, driven by the environmental conditions on that planet and by the accidents of history that can affect living organisms." Find the entire article at: http://argyre.colorado.edu/life/lifeuniverse.html
October 29, 2001