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Past Shows
April 25, 2009
 Download an MP3 of the entire program (22MB).
A History of Violence
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Humans have developed some remarkable cultural foundations over the millennia -- art, science, music and mathematics. But no matter how noble we are, you can't escape the fact we're often unspeakably savage to one another. The dark side of human innovation includes mass warfare, genocide, torture, systematic murder, and spousal abuse. So, where does our propensity for violence and aggression come from? The English philosopher Thomas Hobbes argued it was a natural part of the human condition and that, without society, life was "nasty, brutish and short." The French philosopher Jean-Jacques Rousseau, on the other hand, believed we were a naturally peaceful creature, noble savages trapped in a violent society. Well, over the past few years, a growing number of scientists have joined the debate, exploring the origins of human aggression through the lens of natural selection. And what they're finding tends to back the Hobbesian view that violence is part of our very nature.
Dr. Richard Wrangham, a biological anthropologist at Harvard, has been studying humans' closest evolutionary cousins, chimpanzees, for close to 35 years. In that time, researchers' view of chimps has changed from peaceable and benevolent creatures to a species that commits murder on a regular basis. Dr. Wrangham believes that chimps and early humans likely inherited a primitive form of warfare from their common ancestor and, as distasteful as it may be, it helped us to thrive as a species.
Dr. David Carrier, a comparative physiologist at the University of Utah, thinks there's good reason to view violence as an important selective criterion in our evolution. He argues that one of the reasons our predecessors made the transition from four legs to two was so they could fight more effectively. And he thinks modern humans still show signs of our anatomical specialization for combat.
Dr. Aaron Sell, an evolutionary psychologist at the University of California, Santa Barbara, studies human faces in order to look for evidence that we use facial expressions to make ourselves seem bigger and tougher than we really are.
Dr. Craig Kennedy, a neuroscientist at Vanderbilt University, is interested in finding out what's going on in the brain when we're aggressive. He's found that when mice are given the chance to fight, they show a pattern of brain activation similar to what happens when they have sex or are given addictive drugs like cocaine. And he argues the human brain isn't all that different.
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Perambulating Pinnipeds
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Puijila darwinii, artist's conception by Mark A. Klingler/Carnegie Museum of Natural History
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Pinnipeds - seals, sea lions and walruses - are just one of the groups of land-dwelling animals that have returned to live in the sea. Like whales, manatees and sea-turtles, they were thought to have once had fully land-adapted ancestors who decided that a watery life was a better bet. Until now, however, a fossil of this ancestor has been elusive. Dr. Natalia Rybczynski, a paleo-biologist at the Canadian Museum of Nature, and colleagues have found one on Devon Island, in a remote part of northern Canada. They call it Puijila darwini, and it's a walking seal - a transitional form as the pinnipeds began the process of returning to the sea.
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Gasping Gators
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If you've ever done any high-altitude hiking, you know how hard it is to operate with low levels of oxygen. So it's pretty remarkable that dinosaurs fared so well. After all, when they first appeared on Earth, there was only half the oxygen as there is today. Dr. Tomasz Owerkowicz, an evolutionary physiologist at the University of California, Irvine, was interested in finding out exactly how dinosaurs managed to grow and thrive in a low-oxygen environment. So he got some close relatives of dinosaurs -- American alligators -- and raised them in different levels of oxygen to see how they did. It turns out the lower the level of oxygen, the smaller and slower-growing the alligators were. Dr. Owerkowicz says that dinosaurs were likely able to reach the massive size of a T-Rex only after the planet's oxygen levels began to rise.
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Blood Falls
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Blood Falls, courtesy Peter Rejcek, US National Science Foundation
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For more than 100 years, explorers have noticed the mysterious Blood Falls at the toe of the Taylor Glacier in the McMurdo Dry Valleys of Antarctica. Against the clean white ice of the glacier, a shocking blood-red stain seemed to drip down, as if the life-blood of the glacier was draining away. Dr. Jill Mikucki, of the Department of Earth Sciences at Dartmouth College in New Hampshire, has discovered that, in a way, it is life draining away. The Blood Falls is, in fact, an outlet from a trapped lake deep beneath the glacier. And in that lake is a strange form of microbial life that has survived by breathing iron, which colours the ice red.
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Theme music bed copyright Raphaël Gluckstein.
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