This study reviews an explanatory statistical model targeting cause-aggregated cohort mortality by sex and age as a function of individual genetics; environmental factors with/without impact for selection; and a latent age-specific non-parametric baseline hazard joint for all individuals. The baseline, indicating degenerative biological ageing, is identified up to a multiplicative factor. A summary of results on fitting the model to historical cohort data covering extreme variation in empirical mortality is considered. The explanatory model does not claim to be fully accurate; however, its relevance is justified by its documented capacity to fit a substantial portion of the knowledge, observations and theoretical circumstances about human survivorship over the past two or three centuries, in particular prior to the latter decades of the 19th century when improved prophylaxis and artificial immunization became increasingly widespread with the progress of sanitation and advances of medical technology. Extension of the model to address morbidity by diagnosis and mortality by age and cause associated with selection and environmental impact is discussed and illustrated by an example.