Complex sentence: In 1991, he published "Evolutionary Biology of Aging" exploring a view of the subject based on antagonistic pleiotropy, the hypothesis that aging is caused by genes that have two effects, one acting early in life and the other much later.
Split into simpler sentences: In 1991, he published "Evolutionary Biology of Aging" exploring a view of the subject based on Antagonistic Pleiotropy. This is the hypothesis that aging is caused by genes that have two effects, one acting early in life and the other much later.