As an example of this, a crab claw and pair of scissors share form, such that a person unacquainted with crabs but familiar with scissors could infer that a crab uses its claw to cut.Ī major source of evidence comes from comparative morphology, which infers function through form. Similarly, features in hominin ancestors can be compared to evolutionarily related organisms whose diets are well characterized, such as vegetarian gorillas and omnivorous chimpanzees. Our earliest hominin ancestor, Australopithecus, evolved approximately 4 million years ago, and is characterized by enormous mandibles (lower jawbones), akin to gorillas, which require their large mandibles to effectively crush plant matter. As human evolution progressed, mandibles became more slender while brain size increased, akin to chimpanzees, which eat insects and small mammals in addition to plants. Another major morphological development, which occurred alongside brain expansion, is a reduction in gut length. These two changes are seemingly paradoxical as our brains are metabolically demanding organs, yet a reduced gut length would mean less capacity for absorbing nutrients to fuel a larger brain. Scientists have argued that these morphological changes in hominins were made possible due to a transition from plant to meat-based diets. Meat is easily masticated compared to plants, removing the need for larger and more powerful mandibles, and its fat content makes it energy-dense, matching higher metabolic demands despite a reduced gut length.

Isotopic nitrogen analysis has suggested that the source of this meat was largely terrestrial animals. Notably, isotopic carbon analysis suggests that certain types of plants, primarily starchy in-ground tubers (prehistoric potatoes), remained in ancestral diets following this proposed transition.

Accordingly, modern humans have likely retained these nutritional adaptations to the consumption of meat and starchy plants. The transition from plant to meat-based diets implies an increased consumption of fat and protein relative to carbohydrate.

Msr606 write read utility program