The classical arguments favouring a genetic basis of ageing are reviewed 
emphasizing the questions that remain unanswered. Genes cannot be the sole 
genetic determinants of ageing. 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 ageing. The functions of the largest part of the human 
genome remain unknown. Moreover the different genetic theories of ageing 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 ageing phenomenon.