Humans are the end point of almost four billion years of evolution. The generally accepted explanatory theory is Charles Darwin’s theory of evolution through natural selection, brought on by a struggle for existence. Darwin bolstered his case through a “consilience of inductions,” showing how evolution through selection explained in many areas right across the life sciences – behavior, fossil record, geographical distributions, morphology, taxonomy, and embryology. The missing element was an adequate theory of heredity, supplied by the Moravian monk Gregor Mendel. A major problem was why random change in the units of heredity, mutations of the genes, should provide enough suitable material for selection to work on. Theodosius Dobzhansky solved this problem by hypothesizing that all populations contain much variation, quite enough for selection to work on. His student, Richard Lewontin, using molecular techniques – gel electrophoresis – showed that Dobzhansky’s hypothesis was right.

One might not expect to find eleven immaculately painted plaster chicken heads in a museum of the history of science such as the Whipple Museum. The heads were made in the early 1930s and have been attributed to Reginald Punnett, Alfred Balfour Professor of Genetics at the University of Cambridge from 1912 to 1940. During his long career, Balfour conducted detailed breeding experiments with chickens, experiments that are themselves bound up with the invention for which he is best known today, the Punnett square, a tabular array still used in genetics to represent the outcome of a cross between two organisms. In this chapter, I investigate how both Punnett’s square and his chicken head models, qua visualisations, played different but related roles in the study and teaching of Mendelian genetics and heredity during this crucial period in the development of genetics in Britain. In so doing, I demonstrate that models and their uses in science are most clearly illuminated when their relations to and differences from other forms of visual media, including flat material such as the Punnett square, are made clear.