Day 34: With all due respect, Atkins, carbs helped us evolve

 

The increase in hominin cranial capacity over time. Researchers think the ability to nourish our growing brains is what helped early humans evolve. Credit: Encyclopedia Britannica, Inc.

Carbs may have paved the way for humans to evolve two million years ago, which means low-carb diets could actually be — well, primal.

Anne Stone, an anthropologist at Arizona State University in Phoenix, has been exploring the genetic underpinnings of the human shift to a starchy diet, which may have been a pivotal factor in our long-ago divergence from chimps. Stone is one of many researchers who have been in the spotlight in recent years because they’re uncovering the history of the human diet. In doing so, they’re also learning where that diet has gone awry in developed nations, to yield so-called “diseases of affluence” like diabetes, obesity and heart disease.

And in at least one case, they’re learning that our ancestors might not have been as tough as we think.

Stone and her graduate student, George “P.J.” Perry, have headed up an investigation of how the amalyse gene (AMY1) –  responsible for starch hydrolysis – varies between species.  Individuals with high starch diets have more copies of the gene than those with traditionally low starch diets. Digestion of starches is critically important for energy absorption – especially during episodes of diarrhea. Their research gives insight into why certain populations may weather diarrheal diseases better than others.

“To gain an even better understanding of this process in humans, we analyzed patterns of AMY1 copy number variation in chimpanzees and bonobos. We discovered that the average human has about three times more AMY1 copies than chimpanzees, which eat mostly fruit and far less starch than humans. And bonobos may not have any,” Stone said in a press release. “This human-specific increase may have occurred with a dietary shift early in hominin evolutionary history. We know that starch-rich root plants were a critical food for early hominins, and may even have facilitated the initial spread of Homo erectus out of Africa.”

Hominins are chimp-human ancestors. Scientists believe chimps and humans diverged 5.4 to 6.3 million years ago.

In an email, Stone put those statements into context: “A shift in diet is something that we assume happened, since more calories are needed to grow a big brain, but when and how this occurred is under debate,” she wrote, adding that one question is whether more starch or more meat would have been the catalyst for (or consequence of) human evolution.

Another researcher, anthropologist William Leonard at Northwestern University, has been making the point that the earliest humans needed a suite of rich, high-energy foods — not just carbs — to fuel relatively large brains. A quarter of humans’ resting energy goes toward feeding our brains, considerably more than other primates (about 8 to 10 percent) or other mammals (3 to 5 percent). Also, the higher-quality foods once served to offset the forgaging costs to find them. But reductions of in physical activity for many modern adults have lowered the metabolic costs of survival.

“Think about our ancestors,” Leonard said. “Human hunter-gatherers typically move 8 miles per day in the search for food. In contrast, we can simply pick up the phone to get a meal delivered to our door.”

“Nutcracker jaws”

Peter Ungar, an anthropologist at the University of Arkansas in Fayetteville, is set on addressing what he says is a misnomer: the early ”Nutcracker Man” (Paranthropus boisei), so-named for his wide, flat teeth, mostly ate the ancient equivalent of gelatin. The Nutcracker man was a hominin that lived 1.5 to 2.5 million years ago in South Africa.

The early "Nutcracker Man" (Paranthropus boisei) had wide, flat teeth which at first gave him a reputation for eating tough foods. New research shows that reputation might not be entirely deserved.

“The microscopic scratching and pitting on Paranthropus teeth are quite light, and not what we find today in species that habitually crush hard, brittle foods for a living (like roots, tubers, palm fronds and hard nuts),” Ungar wrote in an email.  ”On the other hand, the pattern resembles that of living soft fruit eaters that only occasionally get into much harder foods.”

Now, Ungar is proposing that the physical adaptation for chewing hard foods may be triggered by crisis situations, rather than everyday dietary needs.

“Many living primates focus their attentions on soft, sugary foods most of the time,” he said. ” They only eat difficult to chew or otherwise metabolically challenging foods when the preferred ones are unavailable.  At those times, species are forced to ‘fallback’ on whatever foods are available, even if they give little energy, and are difficult to chew or digest.”

And those are the times when, historically, Nutcracker man enjoyed a competitive advantage, Ungar thinks.  

“Just because you own a fast sports car doesn’t mean you drive 200 miles per hour every day,” he said. “But if you get chased every now and then, the extra power comes in handy.”

Sources: Eurekalert press releases here, here and here, email exchanges with Anne Stone and Peter Ungar, a 2008 paper by Ungar et al. in the open access journal PLoS ONE, and a dash of Wikipedia (for time frames of hominin and Paranthropus boisei.