I have always been fascinated by the interrelationships and interactions among generations. In airports, I enjoy looking at children and parents and seeing how similar they appear in both looks and actions. After my son was born, I closely observed him as a baby and a toddler to discern the innate character that he had inherited from me or my wife. Of course, whenever he did something that epitomized one of our annoying traits, one of us would knowingly glance at the other with raised eye-brows and think, “Yes, he is definitely your son!” As he grew older, it became more difficult to identify the distinction between genotype and phenotype, that is, between his inherited and his environmentally determined characteristics. And just when I became convinced that he displayed a random mix of our collective genetic backgrounds combined with an imitation of our behavior, he would say or do something completely foreign to both my wife and me. I then pondered whether this novel behavior was some atavistic characteristic of a long-lost relative or an innovation all his own.

Clearly, each of us possesses a particular identity – a unique mix of genetic code, mimicked behavior, and random innovations. I recognize this better than most people because I am a clone – an identical twin – who grew up with my brother in the same household. Despite our shared genetic makeup and virtually identical environment, we are not the same.