Lorna and John have been married for 47 years and have adjusted to the biological changes that have occurred in their sexual arousal, but also have improved their relationship in the process. This is an example of:

Selective Optimization With Selection.

Explanation:

It is known that this theory was widely known from 1980s and was postulated by a man called Baltes. Baltes here argued that as individuals advance through life they are increasingly faced by age related deficits which place limits on their cognitive and behavioral resources. Tackling these limits placed on domains, individuals will begin to invest resources into particular styles and behaviors that are deemed adaptive to the new constraints.