As hominins began occupying different environments, their diets expanded. There are several lines of evidence that can be used to determine what an extinct creature ate including the size and shape of the teeth, marks on the teeth (visible with or without a microscope), and the chemical analysis of bones and teeth. Chemical analysis of teeth enamel suggests that early hominin diets changed drastically at around 3.6 million years ago and that these changes are likely due to changes in the environment. Specifically, this indicated that the early hominin habits, and food availability within them, changed and that early hominins diets shifted to incorporate new food resources.

Different plants produce oxygen using different photosynthetic pathways, and each of these results in different carbon isotope signatures—either a three-carbon compound (C3) or a four-carbon compound (C4). C3 plants include trees, bushes, and shrubs. Grasses and sedges, common in African savannas and deserts, are C4 plants. When animals eat the plants of a given category, these carbon isotopes remain in the tooth enamel. Researchers can analyze the enamel to see what ratio of isotopes exists and to see what foods an organism primarily ate. These isotopes tell us that hominins before this point ate primarily fruits and tree-based vegetation but around 3.6 Ma, expanded their dietary repertoire to a wider variety of plants. This evidence suggests that the environment was changing toward a more savanna landscape rather than a wooded setting. Early hominins were eating food derived from grasses and sedges, perhaps their roots and tubers, and/or animals who fed on savanna vegetation.

Read more about diet and feeding behavior.

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