The Portrayal of Industrial Melanism in American College General Biology Textbooks

Abstract

The phenomenon of industrial melanism (IM) became widely acknowledged as a well-documented example of natural selection largely as a result of H.B.D. Kettlewell’s pioneering research on the subject in the early 1950s. It was quickly picked up by American biology textbooks starting in the early 1960s and became ubiquitous throughout the 1970s, 1980s and 1990s. While recent research on the phenomenon broadly supports Kettlewell’s explanation of IM in the peppered moth, which in turn has strengthened this example of natural selection, textbook IM entries have actually declined in recent years in favor of other examples. In a previous paper, we drew attention to the pivotal role visual aspects played in the introduction of IM into (and its subsequent removal from) textbook accounts. The present article continues this investigation by analyzing textual passages on industrial melanism within a stratified random sample of textbooks from the 1960s to the 2000s. The fact that this example of natural selection was included by multiple publishers independently, in a short period of time, makes it uniquely qualified for a textbook study of this kind. The purpose of the present project was to determine whether these textbooks contain what has come to be known as the standard peppered moth story. Three complete series were also inspected for change across time. Our analysis focused on (1) the amount of text devoted to industrial melanism; (2) what specific science content elements were present; and (3) what, if any, nature of science (NOS) aspects were included. The study documents an increase in the amount of text devoted to industrial melanism over the decades. In spite of this increase, only modest changes in science content and NOS aspects were found.

Appendix: Codes for Questions 2 and 3

Code number
	Question 2: Are there any trends over time in what content is included?
1 Standard	There are two forms of the peppered moth (light and dark)
2	There are three forms of the peppered moth (light, intermediate and dark)
3 Standard	The dark form is controlled by a single gene which is dominant over the light form
4	Intermediate form is controlled by a complex of genes, which is dominant to the light form but recessive to the dark form
5 Standard	Peppered moths fly at night and/or rest on during the day (On trees or other sites)
6 Standard	Moths are eaten by birds. (Moths are eaten by a visual predator)
7 Standard	The moth’s camouflage determines how easily it can be spotted (on resting site) by visual predators/birds
8 Standard	Moth frequencies in a particular area are dependent on relative level of bird predation
9	Moth frequencies in a particular area are dependent on migration from areas where form frequencies are different
10	Melanism in some species was observed before the industrial revolution
11	Other moth species have undergone industrial melanism
	Question 3: Are there any trends in pre-Kettlewell, Kettlewell or post-Kettlewell investigations on IM?
1	Insect collecting is a popular past time in England
2	Amateurs provided data on changes on wing color/pattern in moths
3	Tutt’s explanation of melanic moths
4	Haldane’s survey data on peppered moths
5	Heslop Harrison mentioned by name
6	Harrison’s caterpillar experiments
7	Harrison’s claim of inheritance of acquired traits
8	Controversies with Harrison’s work
9	E.B. Ford is mentioned by name
10	Ford’s explanation of natural selection acting on camouflage and physiological advantages
11	Ford’s role as a mentor to Kettlewell
12 Typical	H.B.D. Kettlewell mentioned by name
13 Typical	Kettlewell’s field investigations
14	Kettlewell’s moth survey
15	Kettlewell’s visibility scores with human observers
16 Typical	Kettlewell’s mark–release–recapture experiments
17 Typical	Kettlewell’s predation observations
18	Kettlewell’s background choice experiments
19 Typical	Kettlewell’s explanation of natural selection by bird predation
20	Controversies surrounding Kettlewell’s work
21	Kettlewell’s leaf-washing experiments
22	The mark–release–recapture experiments called a controlled experiment
23 Typical	The decline of melanics due to clean-air legislation
24	Post-Kettlewell research
25	Post-Kettlewell researchers mentioned by name