Chris Patil examines a contrarian viewpoint on antagonistic pleiotropy and the evolution of aging: "the idea is that genes which benefit an organism early in life but hurt fitness later on can nonetheless be selected, since extrinsic causes of mortality and the inexorable logic of exponential population growth cause the strength of selection to decrease with time ... The theory is an attractive one that has gained popularity among biogerontologists, as more and more findings are announced that appear consistent with its predictions. ... But every theory has detractors as well as adherents ... In a recent opinion in Biogerontology, Parsons launches a spirited attack on the generality of antagonistic pleiotropy ... The author’s main argument is that the requisite conditions for antagonistic pleiotropy are extremely rare in naturally occurring populations, and that environmental stress should be a major driving force in the evolution of longevity. Negative consequences of selectable traits should be less important at the levels of energy intake that actually occur in the wild, he argues; furthermore, he proposes that some of the data in favor of antagonistic pleiotropy are artifacts of the artificially benign environments we create in the lab."