by Roger Valdez
Evolutionary science suggests climate change, energy savings spurred human evolution.
Last weekend I spent some time at home recovering from some oral surgery. It was a welcome respite that allowed me to catch up on some of my favorite television shows, including PBS’ Nova. I downloaded the first of a series called “Becoming Human: Unearthing Our Earliest Ancestors.” The series tries to answer one of the most fascinating questions of evolutionary science: How did apes evolve into human beings and why did Homo sapiens emerge, after millions of years of evolution, as the only human species on planet earth? I was surprised to find that the answer contemporary science has found is connected to two issues we’ve been working on here at Sightline. According to one theory gaining ground, the answer about human evolution has to do with climate change and energy efficiency.
Here is a video preview of the series now airing on PBS (it isn’t nearly as good as this classic clip from 2001: A Space Odyssey, which offers an alternative explanation of human evolution).
The [Variability Selection] hypothesis differs from prior views of hominid evolution . . . According to the VS hypothesis, wide fluctuations over time created a growing disparity in adaptive conditions . . . Key hominid adaptations, in fact, emerged during times of heightened variability. Early bipedality, encephalized brains, and complex human sociality appear to signify a sequence of VS adaptations - i.e., a ratcheting up of versatility and responsiveness to novel environments experienced over the past 6 million years.
Sounds complicated but put simply, when the going got tough, the tough (and smart) got going. As water supplies grew and then shrank creating difficulty for early pre-human and human species, those with the ability to walk to other sources of food and water survived, while other species—more like modern day monkeys—died out. The Nova series suggests that brain development reached a plateau among pre-human and early human species at some point, but then started to take big leaps, resulting in larger more complex brains. Potts argues that those changes were spurred by huge changes in climate which favored species that were smart and agile enough to stay ahead of starvation.
There’s an energy efficiency link too, but it’s not obvious. Another scientist suggests that part of the secret of the success of our earlier ancestors was, obviously, their ability to walk. But why would that make such a big difference? Couldn’t a chimp-like ancestor have just as easily swung from tree to tree or ambled on four legs from a dried up lake to a new water source?
It all comes down to the efficient use of energy. As my colleague Clark Williams Derry has pointed out in his post on SUVs and Snickers Bars and one on bikes and energy, our concepts of energy are woefully out of sync with how energy consumption actually works. Things we assume take lots of energy often don’t, while other things we assume are not energy intensive actually are. Walking upright turns out to be a huge leap forward in the efficient use of energy.
Daniel E. Lieberman, a Harvard anthropologist featured on the Nova program has studied the relative energy used for human and chimp walking. There is no contest: human walking is far more energy efficient that the usual four legged amble of our chimp cousins. When trying to move across many miles of African savanna to a new food source, conserving energy is crucial. Use too much of it and you’ll starve to death, but use your calories efficiently and you’ll make it to the next pile of snickers bars.
In the first installment of the series, Lieberman says that the chimp walk is “poorly designed to withstand the forces of gravity. It has to expend a lot of muscular effort to keep itself from collapsing into a little pile of chimpness, or whatever, with each step.” But walking on two legs is faster and more efficient. Another study by Lieberman and University of Utah biologist Dennis Bramble suggests that the ability to run put even more distance between humans and our monkey cousins.
The series is provocative and fun to watch. But it also relates to issues that the human race faces today. It isn’t a stretch to wonder weather we’ve learned anything from previous effects of climate change, however ancient. Will we use our smarts to make changes in our behavior that reduce climate change? Will we work toward more efficient use of energy? Or will we be a victim of evolution like some of our less fortunate relatives? It is hard to exaggerate the long term importance of policy changes now being considered by governments all over the world. Here in North America, passing cap and trade, creating real energy efficiencies, and tapping into renewable sources of energy. This time our fate is largely in our own hands.
This piece originally appeared on Sightline Daily.
Couldn’t a chimp-like ancestor have just as easily swung from tree to tree or ambled on four legs from a dried up lake to a new water source?
Aside from the energy issue, trees to swing from may have been in short supply as climate change dried forests into savanna and grassland.
Work with Orangutans and the discovery of Ardi has lent support to the idea that bipedalism may have evolved in trees. Though of course that doesn't change that fact that bipedalism, especially the highly refined gait of our genus, is very efficient.