Tiny people have evolved in rainforests because it's where tiny steps are better

Tall people are much less efficient when moving through the jungle

Tall people are much less efficient when moving through the jungle

Batek women in Malaysia. New research suggests that their small height is an advantage for navigating dense jungle environments (Vivek Venkataraman)
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Researchers found evidence that rainforest populations around the world have evolved to be short in order to navigate the dense jungle environment more efficiently.

Historically known as Pygmies, hunter-gatherer groups who have lived in the rainforests of Southeast Asia, Africa and South America are unusually small — often under five feet tall.

Various reasons for this have been suggested by scientists in the past, including perhaps the prevalence of disease or parasites in these rich but challenging ecosystems. But in a new study based on field experiments, researchers found that tall people were significantly less efficient compared to short people when moving through the jungle.

The rainforest environment is full of dense vegetation and obstacles that prevent the ease of movement, according to Dr. Vivek Venkataraman, a research fellow at the Institute for Advanced Study in Toulouse, France, and lead author of the paper.

"If you're walking around and it's very costly to do that, then this will favour the evolution of a shorter stature," explained Venkataraman.

The disadvantage of height

The researchers looked at two rainforest populations in their field experiment: the Batek people of Peninsular Malaysia and the Tsimane people of Bolivian Amazon.

They also recruited residents of larger stature who lived near the rainforests. They had all the participants walk in an open field and then a rainforest to observe differences in the way they walked. 

Video showing some of the traditional practices and hunting and gathering methods of the Batek people

The tall participants, they found, had adopted a much slower walk in a rainforest setting compared to an open setting. But the rainforest people didn't change their gait significantly when they switched environments.  

Venkataraman concluded that tall people are penalized more than short people when traversing through the jungle.

"Tall people were disproportionately more influenced by the cluttered environment than short people," he said. "Walking in a dense rainforest is about 20 to 30 per cent more expensive for a taller person compared to when they're walking around normally."

This is because the dense jungle environment puts a constraint on the step size, which forces tall people, who tend to take long strides, to take much smaller, steps.

Batek women walk single-file through a river bed during a fishing trip in Taman Negara National Park, Peninsular Malaysia. (Vivek Venkataraman)

This disrupts their normal mode of walking and causes them to slow down their movement in order to preserve their natural gait, which scientists found is the most optimal.

As a result, they face a tradeoff between efficiency and speed.  

Short people, on the other hand, generally take smaller steps, so the cluttered rainforest environment didn't affect their gait as much.

Where evolution favours the short

Rainforest groups around the world have evolved to be short independently in order to survive in the tough jungle environment, Venkataraman pointed out.

Batek men and women in Taman Negara National Park, Peninsular Malaysia, search for tubers in the jungle understory. (Vivek Venkataraman)

"[The study] shows that human evolution can proceed quite rapidly in 10 to 20,000 years and that different human populations are actually biologically adapted to living in particular kinds of environments," said Venkataraman. "So even though we live in this highly globalized world today, the distribution of people around the world reflects the very specific environmental pressures as well."

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