Research into link between exercise and evolution provides food for thought

ANYONE whose resolve to exercise in 2013 is a bit shaky might want to consider an emerging scientific view of human evolution.

ANYONE whose resolve to exercise in 2013 is a bit shaky might want to consider an emerging scientific view of human evolution.

It suggests that we are clever today in part because a million years ago we could outrun and outwalk most other mammals over long distances. Our brains were shaped and sharpened by movement, the idea goes, and we continue to require regular physical activity in order for our brains to function optimally.

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The role of physical endurance in shaping humankind has intrigued anthropologists and gripped the popular imagination for some time. In 2004, evolutionary biologists Daniel E Lieberman of Harvard and Dennis M Bramble of the University of Utah published a seminal article in the journal Nature titled ‘Endurance Running and the Evolution of Homo’, in which they posited that our bipedal ancestors survived by becoming endurance athletes, able to bring down swifter prey through sheer doggedness, jogging and plodding along behind them until the animals dropped.

Endurance produced meals, which provided energy for mating, which meant that adept early joggers passed along their genes. In this way, natural selection drove early humans to become even more athletic, Lieberman and other scientists have written, their bodies developing longer legs, shorter toes, less hair and complicated inner-ear mechanisms to maintain balance and stability during upright ambulation. Movement shaped the human body.

But simultaneously, in a development that until recently many scientists viewed as unrelated, humans were becoming smarter. Their brains were increasing rapidly in size.

Today, humans have a brain that is about three times larger than would be expected, anthropologists say, given our species’ body size in comparison with that of other mammals.

To explain those outsized brains, evolutionary scientists have pointed to such occurrences as meat eating and, perhaps most determinatively, our early ancestors’ need for social interaction. Early humans had to plan and execute hunts as a group, which required complicated thinking patterns and, it has been thought, rewarded the social and brainy with evolutionary success. According to that hypothesis, the evolution of the brain was driven by the need to think.

But now some scientists are suggesting that physical activity also played a critical role in making our brains larger.

To reach that conclusion, anthropologists began by looking at existing data about brain size and endurance capacity in a variety of mammals, including dogs, guinea pigs, foxes, mice, wolves, rats, civet cats, antelope, mongeese, goats, sheep and elands. They found a notable pattern. Species like dogs and rats that had a high innate endurance capacity, which presumably had evolved over millenniums, also had large brain volumes relative to their body size.

The researchers also looked at recent experiments in which mice and rats were systematically bred to be marathon runners. Lab animals that willingly put in the most miles on running wheels were interbred, resulting in the creation of a line of lab animals that excelled at running.

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Interestingly, after multiple generations, these animals began to develop innately high levels of substances that promote tissue growth and health, including a protein called brain-derived neurotrophic factor, or BDNF. These substances are important for endurance performance. They also are known to drive brain growth.

What all this means, says David A Raichlen, an anthropologist at the University of Arizona and an author of a new article about the evolution of human brains appearing in the January issue of Proceedings of the Royal Society B, is that physical activity may have helped make early humans smarter.

“We think that what happened in our early hunter-gatherer ancestors is that the more athletic and active survived and, as with the lab mice, passed along physiological characteristics that improved their endurance, including elevated levels of BDNF,” says Raichlen. Eventually, these early athletes had enough BDNF coursing through their bodies that some could migrate from the muscles to the brain, where it nudged the growth of brain tissue.

Those particular early humans then applied their growing ability to think and reason toward better tracking of prey, becoming the best-fed and most successful from an evolutionary standpoint. Being in motion made them smarter, and being smarter now allowed them to move more efficiently.

And out of all of this came, eventually, an ability to understand higher maths and invent iPads. But that was some time later.

The broad point of this new notion is that if physical activity helped mould the structure of our brains, then it most likely remains essential to brain health today, says John D Polk, an associate professor of anthropology at the University of Illinois at Urbana-Champaign, and co-author, with Raichlen, of the new article.

And there is scientific support for that idea. Recent studies have shown, he says, that “regular exercise, even walking” leads to more robust mental abilities, “beginning in childhood and continuing into old age”.

Of course, the hypothesis that jogging after prey helped drive human brain evolution is just a hypothesis, Raichlen says, and almost unprovable.

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But it is compelling, says Harvard’s Lieberman, who has worked with the authors of the new article. “I fundamentally agree that there is a deep evolutionary basis for the relationship between a healthy body and a healthy mind,” he says, a relationship that makes the term ‘jogging your memory’ more literal than most of us might have expected and provides a powerful incentive to be active in 2013.

‘Miracle-Gro for the brain’

Described by some as Miracle-Gro for the brain, the protein brain-derived neurotrophic factor (BDNF) is increasingly proposed by scientists as the key component in understanding the link between physical exercise and our mental ability.

The production of the protein is generated by exercise, then it binds to receptors in the synapses between our neurons, increasing voltage and increasing the brain’s functions.

Once the protein reaches cells it is also known to increase seratonin production, hence it and exercise’s connection with self-esteem and depression.

Daily and short bursts of high-intensity exercise are believed to be best for boosting levels.

A previous German study’s results proved that participants who sprinted for two three-minute bursts (separated by two minutes of lower intensity) during a 40-minute treadmill session demonstrated higher increases in BDNF than

the non-sprinters.

The sprinters learned vocabulary words 20 per cent faster than their counterparts.

Not only does the production of BDNF proteins from exercise increase neuro activity, the proteins also protect the brain from decay, thus leading some researchers to investigate the longer term effects of exercise on diseases such as Parkinson’s disease and Alzheimer’s.

• www.royalsocietypublishing.org

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