The inevitability of the aging process and the onset of senescence – the process of deterioration with age – is a fact of life for most plant and animal species. Some, however, live to extreme ages, such as the English yew, of which at least one alive today is recorded in the Domesday Book; while a few organisms seem to defy current evolutionary understanding altogether, by appearing to have indefinite generation lengths with negligible senescence. For example, the Rocky Mountain Bristlecone Pine is known to produce viable cones at over 4000 years of age.