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Posted on Jul 28, 2005, 8 a.m.
By Bill Freeman
The latest SAGE Crossroads article examines the evolution of evolutionary theories of aging: "The leading evolutionary explanation for aging has reached its silver years. Born in the late 1940s, the theory matured in the 1960s and flourished in the following decades, as researchers amassed evidence supporting its predictions. But like many of its contemporaries, the theory now needs to have a little work done.
The leading evolutionary explanation for aging has reached its silver years. Born in the late 1940s, the theory matured in the 1960s and flourished in the following decades, as researchers amassed evidence supporting its predictions. But like many of its contemporaries, the theory now needs to have a little work done. Evolution experts don't envision a makeover, merely a few nips and tucks to explain some vexing results from field studies and mathematical models.
Sixty years ago, scientists were puzzled by how natural selection would permit organisms to deteriorate and die. Injurious genes get weeded out of a population because they reduce the fitness of creatures that carry them--and therefore don't get passed on to future generations. Then in 1946, immunologist and future Nobel laureate Peter Medawar came up with an explanation that could dispel the confusion. He realized that in the wild, few organisms survive to their golden years (or weeks); most perish from disease, predation, or accidents before they grow old. Detrimental genes, he reasoned, could evade winnowing by natural selection if they don't act up until later in life. Evolutionary biologist George C. Williams added another twist by arguing that some genes persist because they are pleiotropic: beneficial early in life but deleterious at older ages. In 1966, W. D. Hamilton wove these strands of thought into the first mathematical model demonstrating that selection weakens as organisms get older.
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Sixty years ago, scientists were puzzled by how natural selection would permit organisms to deteriorate and die. Injurious genes get weeded out of a population because they reduce the fitness of creatures that carry them--and therefore don't get passed on to future generations. Then in 1946, immunologist and future Nobel laureate Peter Medawar came up with an explanation that could dispel the confusion. He realized that in the wild, few organisms survive to their golden years (or weeks); most perish from disease, predation, or accidents before they grow old. Detrimental genes, he reasoned, could evade winnowing by natural selection if they don't act up until later in life. Evolutionary biologist George C. Williams added another twist by arguing that some genes persist because they are pleiotropic: beneficial early in life but deleterious at older ages. In 1966, W. D. Hamilton wove these strands of thought into the first mathematical model demonstrating that selection weakens as organisms get older.
Read Full Story
