Once upon a time — 3.5 million years ago — our human ancestors decided to expand their dietary options. While they had previously eaten a diet of leaves and fruits from trees and shrubs like that of today’s great apes, new studies of fossilized teeth enamel reveal that, at some point, our ancestors decided to try something new, grasses and sedges, according to four new studies recently published in the Proceedings of the National Academy of Sciences.
This change in diet was key to humans’ development, say scientists. Grazing animals had been eating grasses and sedges (which resemble grasses and rushes) since about 10 million years ago. Our human ancestors’ beginning to eat grassy foods from dry and open savannahs could “signal a major and ecological and adaptive divergence from the last common ancestor we shared with African great apes, which occupy closed, wooded habitats,” according to University of South Florida geologist Jonathan Wynn.
Dietary changes could be linked to larger brain size and also to our ancestors starting to walk upright some 4 million years ago, says Matt Sponheimer, a University of Colorado, Boulder anthropologist. By the time our genus, Homo, evolved around 2 million years ago, it already had larger brains than other primates — could a different diet have played a role?
Notably, we humans today are the only surviving primates whose diet includes more grasses. The scientists’ analysis of many, many fossilized teeth does not indicate exactly what part of grasses and sedges (leaves, stems, seeds, roots) our human ancestors ate or whether they could have been eating insects that ate grasses or meat from grazing animals. (The earliest evidence that we have of our human ancestors scavenging for meat dates back 2.5 million years ago; surefire evidence of hunting dates to only about 500,000 years ago.)
It is possible that we could turn to eating grass again. In a case of “back to the future,” Zhang Percival, a professor of biological systems engineering at Virginia Tech, has developed a process whereby solid cellulose from wood, grass or crop residue such as corn husks can be transformed via enzymes into a carbohydrate called amylose.
That is, Zhang has devised a way to turn “nonfood biomass” such as wood, grass and bushes into something that is edible, contains nutrients and is easily digestible. These properties distinguish the starch produced by Zhang’s method from the cellulose listed as an additive in fast food and many processed foods including ice cream, salad dressing, some meat products and bread.
Zhang’s idea might sound strange. Cellulose is a food additive that manufacturers add to foods to provide bulk, but that’s about all it provides. But the starch in powder form that Zhang has created from wood, grass and similar plants is the sort of thing that astrobiologists at NASA are interested in. The process Zhang has developed might be a way for astronauts to produce food from plants while on long-term missions.
While there has been a bit of talk about space tourism, most of us will (most likely) not be heading into orbit anytime soon. But Zhang’s findings might have applications of a more mundane sort. In view of predictions of food scarcity and nourishing the world’s growing population — at a time when many are eating more meat and concerns have arisen over the amount of arable land available and over water supplies for crops and for livestock — a way to turn any sort of plant into something edible could be called for. It does sound odd to eat grass, but perhaps what was good for our earliest ancestors might be for us again?
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