Research conducted at Duke University reveals what may seem counterintuitive: for small primates (weighing less than 450 grams), moving around in trees doesn’t require more energy than moving around on the ground. This challenges the long-standing evolutionary notion that the first primates took an energetically costly trip into treetops millions of years ago.
The larger the animal, the less oxygen it used while walking.
A team led by Duke’s Jandy Hanna constructed “vertical treadmills” to test just how much energy various species of primates of varying sizes expended while climbing. By measuring the primates’ oxygen consumption, Hanna and her colleagues calculated the energy expenditure of the different animals as they climbed or walked for 15 to 30 minutes.
The experiments showed that size, perhaps unsurprisingly, made a big difference in the energy used by the different species—but what’s surprising is the correlation between size and energy use. The study showed that the primates, regardless of size, used the same amount of oxygen to lift a kilogram of body mass one meter while climbing. But the larger the animal, the less oxygen it used while walking. For example, lemurs and lorises use 12 and 28 times, respectively, more units of energy to cover the same span horizontally than humans.
Thus, the team’s conclusion, reported in Science, is that primates weren’t expending more energy swinging in trees as they grew larger; rather, they would have benefited from the reduced energy costs of walking across the ground (on all fours, of course). Hanna hasn’t yet run the experiment with larger primates, such as macaques and chimpanzees.
What strikes us as interesting is how inflated the conclusions are compared to the actual experimentation done. In fact, this is a perfect example of good observational science contrasted with speculative origins science. What Hanna’s team discovered simply concerned the energy expenditures of various small primates when climbing and walking in the present—these are the facts. But the facts have been stretched over the framework of evolution and have been interpreted in a particular way—as “evidence” in a particular discussion within evolutionary theory (primates’ transition into the treetops). Thus we have passages like these in the ScienceNOW coverage of the research:
"[T]he first primates were likely small and flexible..."
[T]he first primates were likely small and flexible, able to invade a new arboreal habitat without giving up energy. But as primates came down from the trees, they, like nearly all terrestrial animals, benefited from energy-saving tricks and longer stride lengths that reduce the cost of walking in larger animals.
[T]he next step is to run larger primates, such as macaques and chimpanzees, on the vertical treadmill to see if the trend holds for bigger body sizes. That might offer clues as to why human ancestors stayed relatively small until after they had adopted a fully modern style of bipedalism 1.8 million years ago.
Furthermore, as we pointed out earlier, BBC News ran the research under a headline telling of “our ancestors”—more evolutionary interpretation.
Creationists interpret facts, too, and in this case, Hanna’s research shows how different organisms are well suited for their habitats. It is a tribute to our Creator, who, before the Curse, created both habitat and inhabitant in a perfect relationship.
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