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By Kenneth Chang
You are what you eat. A corollary of that adage hominids of 3 million years ago were what they ate has provided paleontologists insight into the diet of our early relatives.
Surprisingly, meat or grass may have been on the menu.
Analyzing carbon atoms locked up in tooth enamel, two researchers challenge the widely held belief that Australopithecus africanus an upright, walking pre-human hominid that lived in southern Africa ate little more than fruits and leaves.
No Steak Knives
This does raise the possibility that the consumption of high-quality animal foods arose significantly before Homo or the earliest stone tools, says Matt Sponheimer, an anthropology graduate student at Rutgers University in New Jersey. For whatever reason, they are doing something different than what we anticipated.
The research looks at four A. africanus fossil skeletons unearthed from South Africa. Living about 3 million years ago, A. africanus may be a direct ancestor of modern humans.
What were trying to do is imbue these cold bones with some life, Sponheimer says.
There arent many clues to deduce the lifestyles of early hominids. How can one figure out the food of creatures that didnt leave behind pots, food wrappers or recipes?
The shape of A. africanus teeth offered the first clues.
Large and blunt with thick enamel, they look ideal for crushing nuts and chewing fruit as opposed to the sharp incisors one would want to rip into meat. The first stone tools, which would help in eating meat, didnt appear until about half a million years later.
Youd basically be crushing the food. The teeth are just not designed for eating meat, says Peter Ungar, an anthropologist at the University of Arkansas who doubts the early hominids ate much meat. Its like imagining pounding a steak with a hammer as opposed to slicing it with a knife.
Anthropologists have also found microscopic scratches and pits on A. africanus molars, possibly caused by chewing on tiny abrasive particles found in many fruit and leaves. The wear patterns are very similar to those food on the teeth of modern-day chimpanzees and orangutans, both primarily fruit eaters.
Sponheimer and Lee-Thorp took a new approach, looking at the chemical composition of the tooth enamel. Unlike fossils, where minerals replace all the original organic material in the bones, the hard, durable enamel remains almost unchanged through millions of years.
Looking for Heavy Carbon
After chipping about two milligrams of enamel with a diamond-tipped dental drill, the researchers analyzed the samples for the isotope carbon-13, which contains one extra neutron in the nucleus compared to the usual form of carbon.
Grasses and related plants known as sedges use a different form of photosynthesis that is more likely to absorb carbon dioxide with the heavier carbon-13. Thus, grasses and sedges contain more carbon-13 atoms than other plants. Animals that eat grasses and sedges likewise have higher carbon-13 levels than those eating fruits and other plants.
What Sponheimer and Lee-Thorp found was that the teeth of A. africanus had an in-between amount carbon-13 more than the fruit eaters, less than the grass eaters.
Which meant not only theyre eating fruits, theyre eating a lot of grasses, or animals eating grasses, Sponheimer says. The lower carbon-13 levels could also come from eating certain types of insects.
What was it about Australopithecus that made it eat these different kinds of foods? he says. Thats the most interesting part of this.
Moving Out of Forests
Sponheimer suggests the changing diet may reflect a move down from the trees in the forests to grassy plains.
Ungar of the University of Arkansas agrees the study offers new suggestions of hominid diet, but discounts the suggestion that meat could explain the lower carbon-13 levels.
I think the work is pretty solid, he says. Its interesting in that it stimulates more discussion on diet, which has been ignored.
Studies of other isotopes in the tooth enamel could provide more clues. Whats great about this study is that it shows we can now get at these issues, comments Kaye Reed, a research associate at the Institute of Human Origins at Arizona State University.
Reed points out that if A. africanus ate grass, it doesnt mean it was grazing in fields. We have this block in our heads, oh my God, they couldnt be eating grass, she says. You picture someone munching out there like a cow.
Roots or seeds of some grasslike plants could have been quite tasty. They could have been eating parts of grass, Reed says. Why not? Were not just talking what you grow on your lawn.
Take good care of your teeth. In 3 million years, an anthropologist might be using them to figure out what you ate for dinner.
S U M M A R Y|
The tooth enamel of Australopithecus africanus suggests the pre-humans ate not only fruits and leaves, but also grasses or animals that ate grasses.
They could have been eating parts of grass. Why not? Were not just talking what you grow on your lawn.
Kaye Reed, Institute of Human Origins