The authors of the study also examined 77 college textbooks in biology and 69 in physical anthropology published between 1932 and 1989. Physical anthropology texts argued that biological races exist until the 1970s, when they began to argue that races do not exist. In contrast, biology textbooks did not undergo such a reversal but many instead dropped their discussion of race altogether. The authors attributed this to biologists trying to avoid discussing the political implications of racial classifications, instead of discussing them, and to the ongoing discussions in biology about the validity of the concept "subspecies". The authors also noted that some widely used textbooks in biology such as Douglas J. Futuyama's 1986 "Evolutionary Biology" had abandoned the race concept, "The concept of race, masking the overwhelming genetic similarity of all peoples and the mosaic patterns of variation that do not correspond to racial divisions, is not only socially dysfunctional but is biologically indefensible as well (pp. 5 18-5 19)." (Lieberman et al. 1992, pp. 316–17)

How many college textbooks in biology did the authors of the study examine?