The Definition of Life What is Life? This is a seemingly simple question to ask, but a difficult one to answer. Different definitions may be possible, from the strictly scientific ones applied by researches in the biosciences to those of philosophers and, of course, including the ideas expressed in the scriptures of the world's religions. Scientific definitions Many different areas of biology have been very busy in studying the various phenomena of life. Evolutionists have studied and compared different forms of life in order to establish their evolutionary relationship, a fundamental property of life according to Miller and other "origin of life" experts. Cell biologists have worked out the basic functioning of organisms, while molecular biologists are trying to understand the molecular mechanisms of these basic functions. Geneticists have been involved in the comprehension of the replication of life, another property related to evolution and which is considered an important property of life, while ecologists have centred their attention on the basic rules that govern the complex relationship between different organisms sharing the same habitat. And this is taking into consideration only biology. Other areas of science, like chemistry, geology, physics and even philosophy, are also trying hard to give an exhaustive, holistic definition of life. But in spite of many different approaches, the hard reality is that we are still lacking an adequate definition of life. This difficulty in defining our object of study adds an important factor of complexity and uncertainty to the discussions of its existence, and especially to the search for life in other parts of the universe. Here are definitions expressed in the Newton magazine (Italian version), in a box within a reportage entitled "Segnali di Vita Aliena" (Signs of Alien Life), published in the June 2001 issue Haboku Nakamura - Biology Institute, Konan University, Kobe, Japan: Living beings are systems that have three simultaneous features: they are self-supported, they reproduce themselves and they evolve through interaction with the environment. André Brack - Centre for Molecular Biophysics of CNRS, France: Life is a chemical system able to replicate itself through autocatalysis and to make mistakes that gradually increase the efficiency of the autocatalysis. Sidney Fox - South Alabama University, USA: Living beings are protein-made bodies formed by one or more cells that communicate with the environment through information transfer carried out by electric impulses or chemical substances, and capable of morpholigical evolution and metabolism, growth and reproduction. Camilo J. cela-Conde - Dept. of Philosophy, University of Baleares: Living beings are beings able to elaborate information in such a way that in the sequence "environmental stimulus - construction of knowledge - motor response", the possible results in terms of input cannot be mechanically predicted. Other definitions [Section to be inserted] Some personal thoughts We asked the members of the Expert Panel and the International Steering Committee to express their thoughts on this subject - here are their answers [more to follow]: Claus Madsen - European Affairs Officer at the European Southern Observatory (ESO) Wubbo Ockels - head of the Education Office European Space Agency (ESA) and ESA Scientist Astronaut Richard West - astronomer at the European Southern Observatory (ESO) What is you own opinion about this?