When does human ageing begin?

Through much of the 20th century, the low point of human mortality was seen at 12-13 years of age. Its stability and timing have been accorded significance in terms of evolution, maximal fitness and the onset of ageing. The nadir of mortality in developed nations now lies at 5-9 years, significantly predating fertility at a mean of 12-13. This differential fall in mortality has resulted in England and Wales primarily but not exclusively from reductions in accidents and deaths from congenital anomalies. The assumption that the nadir of mortality, onset of fertility and a putative intrinsic point of maximal biological fitness are synchronous is disproved by this shift. In this paper the logic of inferring an individual modal pattern of ageing from mean population behaviour is questioned, and the plausibility of the belief that ageing starts at or after fertility is examined. Biological ageing, whether seen as 'wear and tear', programmed change, or cumulative stochastic damage appears to commence at or before conception. Drawing a distinction between 'intrinsic' and 'extrinsic' mortality makes less sense in early than in late life, but indicators of 'intrinsic' diseases are also present from well before fertility. Similarly, measures of fitness other than mortality risk may also be argued to diminish from before birth.