In Chapter 7, Gould provides his rationale for writing this book. One view of science sees the development of knowledge as a movement towards truth, and by the act of debunking false claims; “rotten apples” are removed from the “barrel of accumulating knowledge” (351). However, Gould also notes that science advances “primarily by replacement, not by addition” (352). To debunk a social prejudice, science must provide thorough arguments to “drive out fallacious ideas” (352).

Biologists have confirmed that there is little overall genetic difference between human races; however, human uniqueness lies in its transmission of knowledge from one generation to the next. Cultural evolution is rapid, but also “readily reversible because its products are not coded in our genes” (355). Biological determinism cannot account for cultural evolution in the same way that sociobiology identifies “adaptive behaviors” influenced by the natural selection of genetic variation (356).

As a result, Gould notes the importance of using judicious analogies and inference, and the necessity of moving beyond categories to focus on biological potentialities, rather than biological limits.

In his Epilogue, Gould cites the 1927 Supreme Court case of Buck v. Bell, a Virginia state sterilization law. In 1980, Gould read a newspaper headline related to the 1927 law: “Over 7,500 sterilized in Virginia.