Question

For decades, evolutionary biologists grappled with the paradox of senescence—the inevitable biological decline of organisms. From a Darwinian perspective, natural selection should theoretically favor individuals capable of indefinite reproduction. Early attempts to resolve this paradox relied on group selection models, positing that aging evolved as an altruistic mechanism to clear away older generations, thereby conserving resources for younger, potentially more adaptive offspring. However, this model was fundamentally flawed. Natural selection operates far more effectively on individuals than on populations, and a mutant gene conferring immortality would quickly outcompete "altruistic" aging genes within any group.

The resolution to the paradox lies instead in recognizing that the force of natural selection declines steadily with age. Because mortality from environmental hazards—such as predation or disease—ensures that few individuals reach advanced age in the wild, genetic mutations that cause detrimental effects only late in life face little negative selection pressure. More importantly, through a mechanism known as antagonistic pleiotropy, a single gene can have multiple, conflicting effects. If a mutation provides a significant reproductive advantage early in life, it will be heavily favored by natural selection, even if that same gene causes catastrophic biological degradation in post-reproductive years. Ultimately, therefore, senescence is not a programmed biological function that evolved for the benefit of the species, but rather an unavoidable evolutionary byproduct of the drive for early-life reproductive success.

Which one of the following most accurately expresses the main point of the passage?