PARP-1 activity has also been correlated with maximum lifespan in mammals. The higher the PARP-1 activity, the longer the lifespan. For example, the activity of PARP-1 was measured across multiple mammalian species, and the difference in PARP-1 activity between the longest-lived mammals tested, which were humans, and the shortest-lived mammals tested, which were rats, was fivefold.