"Aging is defined as the progressive deterioration during the adult period that underlies an increasing vulnerability to challenges and a decreasing ability of the organism to survive." (adapted from Masoro & Austad, ref. 1)
And aging matters:
"Discovering the biological basis of aging is one of the greatest remaining challenges for science." (Linda Partridge, ref. 2)
1. Handbook of the Biology of Aging, Seventh Edition (Handbooks of Aging) by Edward J. Masoro and Steven N. Austad
2. Annu Rev Physiol. 2013;75:621-44. doi: 10.1146/annurev-physiol-030212-183712. Epub 2012 Nov 26.
Genetics of longevity in model organisms: debates and paradigm shifts.
Gems D, Partridge L.