Theories of aging have become significantly more important because of discoveries which indicate that aging is not universal or inevitable and which therefore indicate that major medical intervention in aging is possible. Directions of anti-aging research could be significantly influenced by basic theories of aging. Weismann proposed in 1882 that aging was an evolved genetically programmed adaptation that had a species benefit. Since then this idea has been largely replaced by various theories in which aging is not an adaptation but results from accumulated adverse mutations or is an adverse side effect of some essential process. Arguments are presented to the effect that aging is an evolved beneficial characteristic and is therefore likely to result from a more complex and structured mechanism than if it resulted from more random processes such as mutation accumulation. Further, aging appears to be one of a number of related and interactive life-cycle characteristics including age-at-puberty suggesting that it might be controlled by similar biological mechanisms.