Slithering through history: Snakes have been primates’ predators, prey and competition


ResearchBlogging.orgIn pre-colonial Mexico, the winged serpent Quetzacoatl was worshipped as a god. In modern-day Texas, rattlers are regularly fried and eaten. And in Pennsylvania, the snakes at the Philadelphia Zoo’s reptile house have quietly gone about their business while my girlfriend stood in the corner, eyes squeezed shut, shaking with fear.

People’s feelings toward, and relationship with, snakes have varied greatly depending on the time period, location and culture. Today in the U.S., if fear isn’t the most common reaction (it was our #1 fear 10 years ago), then it’s at least very high profile…


You might assume it’s an old fear, too. Certainly our ancestors, whether two hundred or two million years ago, encountered snakes more often than most of us do. In a new study published this week in Proceedings of the National Academy of Sciences, anthropologist Thomas N. Headland and ecologist Harry W. Greene suggests that pre-modern humans and the lower primates have indeed had a long shared history with snakes, and its more complex than we had thought. Because constrictors usually swallow their prey whole and intact and venomous snakes attack soft tissue, there’s almost nothing in the fossil record to tell us anything about snakes attacking and/or eating humans and other primates. To figure out the relationship extinct hominins and pre-modern humans might have had with snakes, examining bones wouldn’t cut it, so the Headland and Greene had step back in time, in a way.

In 1962, three weeks after their wedding, Headland and his wife left Minnesota for the Philippines. For the next 24 years they lived among the Agta Negritos, the indigenous people of Luzon, the country’s largest island. By the time the Headlands arrived, the Agta couldn’t fairly be called primitive, but their lifestyle and size made them both similar to our prehistoric hominin ancestors and susceptible to attacks from large snakes. They were only recently hunter-gatherers and nomads, living in temporary shelters in family-based groups and subsisting on foraged plants and wild meat from the rainforest. Adult male Agta are, on average, a little under five feet tall and tip the scales at 97 pounds, while the reticulated pythons (Python reticulatus) that share the rainforest with them grow as long as 23 feet and weigh in at 165 pounds. An Agta male walking through brush is not only open to an attack from a big python, but also just the right size to be considered a decent meal for a snake, which has been known to eat pigs as big as 130 pounds.

Sure enough, when Headland started interviewing the Agta in the mid-1970s about their experiences with pythons, 15 of 58 men and 1 of 62 women said a python had attacked them. Of the men, two had been attacked twice and 11 still had scars from their attack. The interviewees could also collectively remember six people who were killed by pythons in the previous 40 years, including a man who’s son found the snake, cut it open and retrieved his body for burial.

The hunters also became the hunted sometimes. Every Agta man interviewed said they had killed at least one small python (up to six feet) during their lives, and some had killed larger ones. While Headland was living with them, an Agta hunter shot a 22-foot-long python and butchered it for some 55 pounds of meat.

The 22.6-foot reticulated python, shot by Kekek Aduanan (right) on June 9, 1970

The skin of the same python, post-butchering.

When the Agta and the pythons were not stalking each other, it turns out they were often hunting the same game. Until the 1970s, the Agta routinely hunted and ate Philippine deer, Philippine warty pigs and long-tailed macaques, three species that they often found in the bellies of the snakes they butchered.

The Agta and the pythons, the interviews make clear, have had a complex relationship, acting as each other’s predator and prey, and even directly competing for resources. Headland wanted to see if these same relationships showed up elsewhere in our family tree, so he turned to Cornell ecologist Harry Greene, who searched the natural history literature for primate-snake encounters and found a batch of stories that make the serpent in the Garden of Eden look like nothing. While no living serpent feeds exclusively on primates, Greene found anecdotal evidence that several constrictors prey on them regularly, and that venomous and constricting snakes have attacked at least 26 species of non-human primates, including lemurs, lorises, tarsiers, eight species of New World monkey and ten species of Old World monkey.

Green found that, like the Agta, nonhuman primates have stood up to snakes and attacked them. He found stories of capuchins using branches to kill a terciopelo, and lemurs ganging up on Madagascan ground boas. In some of these battles, the primates were probably defending themselves, but snakes are also potentially great prey choices for a primate, since their flesh isn’t toxic and they stay and confront attackers instead of fleeing.

Scientists have found in other animals, and even plants, that the shadow of an enemy looms long. Could it be that modern humans’ ophidiophobia is the relic of our long shared history with snakes? Is my girlfriend’s uneasiness an ancient, hard-wired instinct kicking in? Well, that’s tricky. Previous research has shown that very young children can detect snakes quicker than other objects, with the researchers suggesting that this is because they’re evolutionarily relevant threats. Subsequent research found that even with this quick detection, kids don’t associate fear, or any other emotion, with snakes until they learn to do so from adults. They only make the connection after seeing the reactions of people around them. If you see a snake, and your mom freaks out, you’ll learn to fear them, too, pretty quickly. Carnegie Mellon psychologist David Rakison, who did the research, points to the late crocodile hunter Steve Irwin’s kids, as examples of the opposite reaction. Irwin worked with dangerous animals very closely without any outward signs of fear, and his kids learned from that (sometimes very up close). Now, both kids are following in their dad’s footsteps.

Even though he and Headland don’t draw any conclusions about the question in their study, Greene told Cosmos magazine that he could “easily entertain as logical the hypothesis” that our fear of snakes is genetic and may formally investigate this in the future. Until we get a better idea of why fear of snakes is so seemingly widespread, it’s fascinating and sort of comforting for now to know that almost all members of our primate family have tangled with them. Since we came down from the trees, and maybe even while we were still in them, we’ve been listening carefully for a rustle in the leaves and a soft, low hiss.

References: 

de Lange, Catherine, (2011). “Fear of snakes? This could be why.Cosmos.

Headland TN, & Greene HW (2011). Hunter-gatherers and other primates as prey, predators, and competitors of snakes. Proceedings of the National Academy of Sciences of the United States of America PMID: 22160702

Yong, Ed. (2011). “Meet the Agta, a tribe where a quarter of men have been attacked by giant snakes.” Not Exactly Rocket Science. 

Images: Beauty comes in all sizes and shapes :)” by spisharam; Python and Agta photos courtesy of Thomas N. Headland


 

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