ABSTRACT
This selection addresses possible objections to the evolutionary arguments presented in the previous selection and shows that questions about life expectancy, genetic change, and human adaptability support rather than challenge the evolutionary model. The selection adds important pieces to the picture of human health history developed in this book and explains a number of key concepts concerning changing disease patterns. One such concept is life expectancy. As noted by Lock in selection 2, the rise in life expectancy since the 1800s does not mean that the human life span has increased, or that there are now old people whereas in the past there were none. Instead, higher life expectancy rates indicate that fewer people die as infants or children and more people live into old age. Another point this selection clears up is the meaning of the apparent confinement of the impact of modern lifestyles to the older age ranges, which may give the impression that people can adapt biologically to the altered environment. However, the seeds for degenerative disease are planted in youth, although signs such as atherosclerosis or elevated blood pressure may be hidden.
