They explained that teeth contain isotopes that lock in information about what the individual ate. Here's how that works: Plants can be divided into three categories based on their method of photosynthesis: C3, C4 and CAM. C3 plants (trees, shrubs, and herbs) can be chemically distinguished from C4/CAM plants (grasses, sedges, and succulents) because the latter incorporate higher amounts of the heavier isotope carbon-13 into their tissues. When the plants are eaten, the isotopes become incorporated into the consumer's tissues. These include the enamel of developing teeth.
Demonstrating the sturdiness of well-preserved teeth in the fossil record, the relative amounts of carbon-13 in such teeth can be read by scientists millions of years after the individual's demise. Your veggie lifestyle, or not, is therefore locked into your teeth seemingly forever.
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The 4 new papers, Alemseged said, "present the most exhaustive isotope-based studies on early human diets to date. Because feeding is the most important factor determining an organism's physiology, behavior and its interaction with the environment, these finds will give us new insight into the evolutionary mechanisms that shaped our evolution."