1 Our Comfort Zone As we get older we develop a greater sense of mortality and we start reflecting on whether our life has been happy, has it been worthwhile, has it been successful? But what do we mean by worthwhile or successful? We might think somewhat hedonistically in terms of the possessions we have accumulated or we might consider longevity and quality of life as evidence of a successful life. Then we might think of some possible lasting impressions that we believe we have made on others. This is particularly true if we have children, and we wonder whether they reflect the values and ideals we have ourselves. Most of us who have children would in a sense see their existence and their achievements as the clearest evidence of our successful lives. Further, for many older members of society, a highly significant and gratifying moment in their lives occurs if they become grandparents. When biologists think about animals and successful lives they use remarkably similar concepts. The most important questions for them are whether the organism has successfully reproduced and whether its progeny have in their turn lived to reproduce. Generally biologists use the word ‘fitness’ to describe this success. Natural selection acts to select characteristics or traits that confer greater fitness within a given environment. In different environments different traits may be more advantageous. Thus after a change in vegetation produced by a change in climate, birds with blunter beaks rather than sharper beaks may have an advantage and be selected preferentially—indeed this is what has been observed in the studies by Rosemary and Peter Grant of the finches of the Galapagos.1 A basic principle of evolutionary biology is that evolution is driven by variation in characteristics within a population (that is, not all individuals are identical), and this variation is reflected in different levels of survival and reproductive success—so some individuals will have more offspring, others fewer. Provided that there are genetic components underlying their
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