Blackwell Reference Online

Extract

Biology is conventionally defined as the science of life. Philosophers, and scientists when they wax philosophical, wonder what being alive amounts to. Should life be defined in terms of the molecule DNA? Well, we know that organisms pass traits to their offspring by transmitting genes to them, and genes are made of DNA. These offspring begin life as one-celled organisms; the genes they contain and the environments they occupy then lead them to grow into multi-cellular organisms containing many different types of cell. Thus, DNA is fundamental to the processes that comprise heredity and development. DNA and RNA are central to organic processes as they occur on earth. But must life be based on DNA and RNA? Could other molecules play the same role in heredity and development? What we earthlings call ‘organic chemistry’ is the chemistry of carbon compounds, but could life forms, if they exist in other galaxies, be built out of silicon? Perhaps it is parochial to think of life in terms of the physical structures that happen to mediate life processes on earth. Is it possible to provide more general and more abstract criteria for what it takes to be alive? As already mentioned, organisms reproduce, pass traits to their offspring, and develop in the course of their lifetimes. In addition, they extract energy from their environment and use this energy to repair tissue damage and to engage ... log in or subscribe to read full text