This activity guides the analysis of a published scientific figure from a study on prehistoric human food sources. In this study, scientists used carbon isotopes to determine how the advent of agriculture affected human diets.

Different types of plants contain different ratios of carbon isotopes. When animals eat plants, the carbon isotopes are stored in their tissues, including bone collagen. In this study, scientists measured carbon isotopes in early human skeletons from North American. The figure shows data of carbon isotope ratios from skeletons found in Illinois, Ohio, and West Virginia dated 4000 BCE to 1500 CE. Each point corresponds to a different location; the numbers and sexes of the individuals found at that location are shown in parentheses. The “Educator Materials” document includes a captioned figure, background information, graph interpretation, and discussion questions. The “Student Handout” includes a captioned figure and background information. The original article is also provided as a download.