The classical arguments favouring a genetic basis of aging are reviewed emphasizing the questions that remain unanswered. Genes cannot be the sole genetic determinants of aging. Mendel's paradigm cannot anymore explain all the results recently obtained. Different aspects of the organization of the genome must also play a role in aging. The functions of the largest part of the human genome remain unknown. Moreover the different genetic theories of aging are based on natural selection. However, other paradigms are being proposed that can complement or replace Darwin's paradigm. They are based on the spontaneous organization of complex systems. They must be considered in the reappraisal of the aging phenomenon.