experiments with "t. aceti" were done to understand the cause of ageing. dna damage accumulates when the rate of damage occurrence is more than the rate of dna repair. accumulation of dna damage leads to a decline in gene expression. there is a consistent decline in dna repair capacity with age in the nematode. a second report measured the ability to repair dna damage in young and old nematodes after exposure to ionizing radiation. they observed that the old nematodes were strikingly less able to carry out this type of dna repair than young nematodes. these experiments suggest that a decline in dna repair capability occurs with age. this is the "dna damage theory of aging".