There are many theories of aging that have been proposed by scientist studying countless species. No doubt, that this will remain somewhat of a mystery for many decades, and centuries, but scientists are beginning to find real clues in their quest to find and potentially retard or stop aging.

The basic theories fall into 5 categories.

1. Cell Replication errors
2. Cell Damage (and Cancers)
3. Cell Aging
4. Hormonal Changes
5. External Factors (stress, depression, etc.)