In summary, evolutionary biologists' claim that aging is not generally programmed does not rest on theory alone as Bredesen suggests. It also rests on observations. Two of these are that the aging phenotype as well as age-at-death are highly variable and occur by no known stereotypical process even within genetically identical individuals reared and maintained in identical environments, and that the well-known instances of programmed organismic death as represented by salmon differ substantially from the type of death seen among other organisms. It is not surprising that biologists who focus their research on genetic or signal transduction pathways should develop a worldview that emphasizes stereotyped, sequential processes. Indeed, it is now clear that such processes contribute to aging in many animals. it is equally clear to me that calling such contributions a program misleads us about the essential nature of aging, which is increasing decay and an attendant loss of regulation. The field of biogerontology will only again, however, from a continuing dialogue among bilogists from a variety of worldviews. © Blackwell Publishing Ltd/Anatomical Society of Great Britain and Ireland 2004.