June 2020
Vol 6, Issue 23

About The Cover

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ONLINE COVER Previous research has shown that maize was first domesticated roughly 9,000 years ago, and prior isotopic studies have indicated that the crop reached staple status throughout much of Mesoamerica by about 3,000 years ago. But anthropologists have so far been unable to determine exactly when and how quickly this transition occurred, due to a lack of evidence of direct consumption. Kennett et al. addressed this knowledge gap by studying two relatively dry and well-preserved sites, named Mayahak Cab Pek and Saki Tzul, that together provide a largely uninterrupted 10,000-year record of human remains. Here, they found 52 individuals buried at a wide range of depths within the shelters. The researchers determined each individual's level of maize consumption by leveraging a defining characteristic of maize: unlike most other consumable forage plants native to the region, maize employs the relatively rare C4 photosynthetic pathway. This metabolic quirk imparts a distinct carbon isotopic fingerprint, which is preserved in both the collagen proteins and apatite minerals in the bones of maize consumers. The results indicate that maize began to take on an increasingly important dietary role for humans in Mesoamerica roughly 4,700 years ago, and within 700 years it had become a true staple crop, accounting for as much as 70% of total diet. [CREDIT: MICHAEL CLUTSON/SCIENCE SOURCE]