LIFE STAGES IN BIRDS AND AGING THEORIES

The durations of the life stages in birds (embryogeny, ontogeny, matur ity) can be measured using physical or physiological timescales. These two methods are compared. Embryogeny has a duration of 10-90 days or 2 +/- 0.8 kJ g-1, ontogeny lasts 20-300 days or 20-40 kJ g-1 and adult stages fall within the range 8-120 years or 2400-4300 kJ g-1. It foll ows that, considered in physiological time units, all birds show more or less the same duration for each life stage. This supports an aging theory, Rubner's law, postulated in 1908, which states that a genetica lly programmed lifespan can be described in terms of an absolute metab olic scope. Within a taxon all organisms appear to have identical phys iological lifespans. Various other theories of aging are discussed.