 The non-adaptive theory assumes that the evolutionary deterioration of human age occurs as a result of accumulation of deleterious mutation in the germline.These deleterious mutations start expressing themselves late in life, by the time we are weak/wobbly and have already reproduced, this means that Natural selection cannot act on them because reproduction has ended.Studies done one "Drosophila melanogaster" have shown an inverse relationship between the mean optimal age at maturity and mutation rates per gene.