A genealogist is a person who traces or studies the descent of people. A census is an official count of a population, typically recording details of individuals.Census sounds like senses. Senses encompass different organs that help a person understand the world around them by allowing the person to experience sight, smell, hearing, taste, and touch. When people age, their senses dull. This joke is playing on the word census which sounds like senses.
Old genealogists never die , they just lose their census .