For the past century, scientists have debated whether or not ageing is directly selected by evolution. Because ageing occurs, by definition, late in life - that is, after the organism’s development is complete - many people believe that it cannot be actively selected for as a process. Furthermore, because it reduces an individual’s fitness, it is thought unlikely to be selected for. In agreement with this viewpoint, numerous theories have been proposed in the last 75 years to explain the observation of its widespread presence in the realm of life. The bd model of ageing is based on a simple life-history trait model that we recently introduced. Our model suggests that senescence can be positively selected through evolution due to the increased evolvability it confers on organisms, not through a specific mechanism but through a ‘function ageing’, limiting organismal maintenance and reproduction. It confirms the substrate for mutation accumulation and antagonistic pleiotropy theories while providing an elegant explanation for the apparent tradeoff between longevity and fertility that led to the disposable soma theory without requiring an energy tradeoff. Furthermore, it predicts that the Lansing effect will be present in organisms that exhibit rapid post-reproductive senescence. This formal and numerical modeling of the evolution of ageing also provides new hints for testing the validity of existing theories.