Are humans a galactic oddity or will complex life with human abilities develop on planets with
environments that remain habitable for long enough? In a clear jargon-free style two leading
researchers in the burgeoning field of astrobiology critically examine the major evolutionary
steps that led us from the distant origins of life to the technologically advanced species we
are today. Are the key events that took life from simple cells to astronauts unique occurrences
that would be unlikely to occur on other planets? By focusing on what life does - it's
functional abilities - rather than specific biochemistry or anatomy the authors provide
plausible answers to this question. Systematically exploring the various pathways that led to
the complex biosphere we experience on planet Earth they show that most of the steps along
that path are likely to occur on any world hosting life with only two exceptions: One is the
origin of life itself - if this is a highly improbable event then we live in a rather empty
universe. However if this isn't the case we inevitably live in a universe containing a myriad
of planets hosting complex as well as microbial life - a cosmic zoo. The other unknown is the
rise of technologically advanced beings as exemplified on Earth by humans. Only one
technological species has emerged in the roughly 4 billion years life has existed on Earth and
we don't know of any other technological species elsewhere. If technological intelligence is a
rare almost unique feature of Earth's history then there can be no visitors to the cosmic zoo
other than ourselves. Schulze-Makuch and Bains take the reader through the history of life on
Earth laying out a consistent and straightforward framework for understanding why we should
think that advanced complex life exists on planets other than Earth. They provide a unique
perspective on the question that puzzled the human species for centuries: are we alone?
