Life’s Biochemical Complexity

Introduction Since our childhood we have been able to sense that the world that surrounds us comprises living things and inert objects, which usually differ from each other by qualities that seem easily recognisable. Thus, we can distinguish that a plant, a fish or an insect belong to the first group of entities, while any liquid substance, air, stone or machine belong to the second. Biology, with its numerous subdivisions (ecology, physiology, genetics, biochemistry, etc.) is the science that studies living beings. Despite the extraordinary advances of this science in both basic and applied (biotechnology), it is paradoxical that the efforts of biologists to reach a formal definition of life have proved unsuccessful.1 This issue does not only have intrinsic intellectual or academic interest. Astrobiology, which is the science that studies the existence and evolution of life in the universe, requires certain criteria, if the opportunity ever arose, to be able to conclude that life has been found on a celestial body other than earth. Furthermore, there have been attempts by synthetic biology to obtain life de novo in the laboratory. What qualities should an entity fabricated by scientists possess so that we would consider it to be alive? Finally, if we concurred that the origin of life on earth did not come about suddenly by a fortuitous coincidence of numerous environmental conditions, but that it happened gradually, would we all unequivocally agree to distinguish at what point during these successive stages life began? Efforts made from other natural sciences to define life, such as in physics or chemistry, have also proven unsuccessful. The difficulty undoubtedly stems from the fact that life is a complex phenomenon that transcends the