When I was a young chemistry student I bought an old organic chemistry textbook from the 1920’s because it was cheap and I read the Introduction and I remember that it had a phrase in it that stuck with me, “Life is the mode of action of albuminous substances.” At the time I puzzled over this sentence, unexpected in a chemistry text. Soon I realized that since albumin is a ubiquitous type of protein, for example in egg white and humans, that “albuminous substances” was an old-fashioned synonym for “proteins.” Since there are literally hundreds of different proteins in the human body, structural proteins such as collagen, functional proteins such as enzymes and transportation proteins such as hemoglobin, it was natural then to believe that they were the chemical basis of life.
Later work by Avery and his co-workers in 1944 at the Rockefeller Institute in NY (before Watson and Crick) showed that DNA, dexoyribose nucleic acid, is in fact the genetic substance. So if we update the chemical definition of life we should say that “Life is the mode of action of DNA.” The genetic code of DNA is responsible for all aspects of life; all phenotypes, all development and all biological characteristics are a manifestation of the function of DNA. It is DNA that as discrete genes expresses the proteins of the body, each of which has a specific and necessary physiological function. You can really say “my genes made me do it.”
To some this may seem overly simplistic and to others it may seem too deterministic. After all, life is also a complex combination of human experiences. There are some religions, notably Buddhism, that consider life to be a mere illusion. Once I was driving my daughter home from an evening meeting of her youth group and she asked me “Daddy, how do we know that life is not an illusion?” (I assume there had been an earnest youthful discussion). I thought for a moment and said “see the lights of the car ahead of us, if I don’t press the brakes right now we will both find out that life is not an illusion.” We experience life in all its glory and pettiness, reality is a harsh taskmaster. Our organism has evolved a nervous system that enables us to experience the reality around us through our senses and through the interpretation of the sensory signals in our brains. Our brains, hands and eyes have evolved so that we can function in a three dimensional universe. I truly believe that it is real and that there is no other universe that we can experience. So don’t forget to press the brakes!