I recently posted on a young preacher who was bitten by a rattlesnake during a snake handling church service. Some people took exception to my characterization of the young preacher as a “fool”.
I am sorry if I stepped on anyone’s toes. To me handling snakes to prove my faith is, er, silly.
Since I am the resident crank, er make that (pseudo)anthropologist I thought it might be interesting to discus why so many of us are terrified of snakes. After all understanding your fears is the first part of dealing with them. Unless you mess with snakes you stand almost no chance of getting bit. Many more people die from bee stings then snake bits. In Kentucky most of those who get bit with venomous snakes are drunk and playing with them. I have ran into venomous snakes in the wild about 5 times and as when I was younger I spent a lot of time in the woods in eastern Kentucky. And none of the encounters was especially dangerous.
The proper name for “fear of snakes” is Ophidiophobia.
As usual my ever so helpful comments will be in (), {}, or [].
- - - - - -
From http://www.pnas.org/content/early/2013/10/23/1312648110
Proceedings of the National Academy of Sciences
www.pnas.org
Pulvinar neurons reveal neurobiological evidence of past selection for rapid detection of snakes
Edited by David M. Hillis, University of Texas at Austin, Austin, TX, and approved October 1, 2013 (received for review July 4, 2013)
Significance
The present study shows preferential activity of neurons in the medial and dorsolateral pulvinar to
images of snakes. Pulvinar neurons responded faster and stronger to snake stimuli than to monkey faces, monkey hands, and geometric shapes, and were sensitive to unmodified and low-pass filtered images but not to high-pass filtered images. These results identify a neurobiological substrate for rapid detection of threatening visual stimuli in primates. Our findings are unique in providing neuroscientific evidence in support of the Snake Detection Theory, which posits that the threat of snakes strongly influenced the evolution of the primate brain. This finding may have great impact on our understanding of the evolution of primates.
Abstract
Snakes and their relationships with humans and other primates have attracted broad attention from multiple
fields of study, but not, surprisingly, from neuroscience, despite the involvement of the visual system and strong behavioral and physiological evidence that humans and other primates can detect snakes faster than innocuous objects. Here, we report the existence of neurons in the primate medial and dorsolateral pulvinar that respond selectively to visual images of snakes. Compared with three other categories of stimuli (monkey faces, monkey hands, and geometrical shapes), snakes elicited the strongest, fastest responses, and the responses were not reduced by low spatial filtering. These findings integrate neuroscience with evolutionary biology, anthropology, psychology, herpetology, and primatology by identifying a neurobiological basis for
primates’ heightened visual sensitivity to snakes, and adding a crucial component to the growing evolutionary perspective that snakes have long shaped our primate lineage.
- - - - -
(Don’t you love the things the government finds worthwhile to spend our precious money on.)
And
- - - - -
“Fear of snakes is one of the most common phobias, yet many people have never seen a snake in person.
“So how is this fear generated?
“New research suggests humans have evolved an
innate tendency to sense snakes — and spiders, too — and to learn to fear them.
“Psychologists found that both adults and children could detect images of snakes among a variety of non-threatening objects more quickly than they could pinpoint frogs, flowers or caterpillars. The researchers think this ability helped humans survive in the wild.
"The idea is that throughout evolutionary history, humans that learned quickly to fear snakes would have been at an advantage to survive and reproduce," said Vanessa LoBue, a post-doctoral fellow in psychology at the University of Virginia. "Humans who detected the presence of snakes very quickly would have been more likely to pass on their genes."
(In other words, those who weren’t afraid of snakes got bit and didn’t live to pass on those genes…)
“Previously, anthropologists have suggested the need to notice snakes in the wild may have led early primates to develop better vision and larger brains.
Eew!
The researchers were inspired to investigate the fear of snakes when they thought about how universally people dislike the slithering legless lizards.
"This feeling is really common," LoBue told LiveScience. "We don’t see snakes all the time. There's really no reason for this overwhelming disgust or hatred of snakes."
LoBue's collaborator, Judy DeLoache, a professor of psychology at the University of Virginia, happens to be petrified of snakes.
"I have almost a phobia of snakes," DeLoache said. "When I see a picture of a snake, I'm like, "Oh my God, eew! The reason we got into this research was
because I've always been fascinated by how it is that people develop it. My intuition was that there was something that made me feel afraid of snakes early on. You react to them very early on."
While babies and very young children do not usually fear snakes, they are unusually skilled at detecting them and show a predisposition to learn to fear snakes if they have bad experiences or even if they are exposed to negative portrayals of them in the media, the scientists found.
Spiders, too
To learn more, the psychologists showed adults and 3-year-old children images of a snake surrounded by objects of similar colors, such as frogs, caterpillars and flowers. Then they showed them pictures of a frog or a flower surrounded by snakes. Both groups were able to identify the hidden snake faster than the other hidden objects.
"We also did a study with spiders and found the same effect," LoBue said. Although the team has not tested other phobias, they don't think these predispositions would necessarily apply across the board.
"It would have to be something widespread, that you could encounter on a day-to-day basis," she said. "That’s why you don’t see lion and tiger and bear phobias as often. It would also have to be something that was around and dangerous while humans were evolving. Things that are dangerous right now, like guns, we haven’t had enough time to develop a predisposition to detect really quickly."
The results of the new study appear in the March 2008 issue of the journal, Psychological Science.
- - - - -
http://www.livescience.com/4183-fear-snakes-drove-pre-human-ev...
An evolutionary arms race between early snakes and mammals triggered the development of improved vision and large brains in primates, a radical new theory suggests.
The idea, proposed by Lynne Isbell, an anthropologist at the University of California, Davis, suggests that snakes and primates share a long and intimate history, one that forced both groups to evolve new
strategies as each attempted to gain the upper hand.
To avoid becoming snake food, early mammals had to develop ways to detect and avoid the reptiles before they could strike. Some animals evolved better
snake sniffers, while others developed immunities to serpent venom when it evolved. Early primates developed a better eye for color, detail and movement
and the ability to see in three dimensions—traits that are important for detecting threats at close range.
Humans are descended from those same primates.
Scientists had previously thought that these traits evolved together as primates used their hands and eyes to grab insects, or pick fruit or to swing through trees, but recent discoveries from neuroscience are casting doubt on these theories.
"Primates went a particular route," Isbell told LiveScience. "They focused on improving their vision to keep away from [snakes]. Other mammals couldn't do that. Primates had the pre-adaptations to go that way."
Harry Greene, an evolutionary biologist and snake expert at Cornell University in New York, says Isbell's new idea is very exciting.
"It strikes me as a very special piece of scholarship and I think it's going to provoke a lot of thought," Greene said.
Isbell's work is detailed in the July issue of the Journal of Human Evolution.
A new weapon
Fossil and DNA evidence suggests that the snakes were already around when the first mammals evolved some 100 million years ago. The reptiles were thus among the first serious predators mammals faced. Today, the only other threats faced by primates are raptors, such as eagles and hawks, and large carnivores, such as bears, large cats and wolves, but these animals evolved long after snakes.
Furthermore, these other predators can be safely detected from a distance. For snakes, the opposite is true.
"If you see them close to you, you still have time to avoid them," Isbell said. "Primate vision is particularly good at close range."
Early snakes killed their prey using surprise attacks and by suffocating them to death—the method of boa constrictors. But the improved vision of primates, combined with other snake-coping strategies developed by other animals, forced snakes to evolve a new weapon: venom. This important milestone in snake evolution occurred about 60 million years ago.
"The [snakes] had to do something to get better at finding their prey, so that's where venom comes in," Isbell said. "The snakes upped the ante and then the
primates had to respond by developing even better vision."
Once primates developed specialized vision and enlarged brains, these traits became useful for other purposes, such as social interactions in groups.
Seeing in 3D
Isbell's new theory could explain how a number of primate-defining traits evolved.
For example, primates are among the few animals whose eyes face forward (most animals have eyes located on the sides of their heads). This so-called
"orbital convergence" improves depth perception and allows monkeys and apes, including humans, to see in three dimensions. Primates also have better color vision than most animals and are also unique in relying heavily on vision when reaching and grasping for objects.
One of the most popular ideas for explaining how these traits evolved is called the "visual predation hypothesis." It proposes that our early ancestors were
small, insect eating mammals and that the need to stalk and grab insects at close range was the driving force behind the evolution of improved vision.
Another popular idea, called the "leaping hypothesis," argues that orbital convergence is not only important for 3D vision, but also for breaking through camouflage. Thus, it would have been useful not only for capturing insects and finding small fruits, but also for aiming at small, hard-to-see branches during
mid-leaps through trees.
But there are problems with both hypotheses, Isbell says.
First, there is no solid evidence that early primates were committed insectivores. It's possible that like many primates today, they were generalists, eating a variety of plant foods, such as leaves, fruit and nectar, as well as insects.
More importantly, recent neuroscience studies do not support the idea that vision evolved alongside the ability to reach and grasp. Rather, the data suggest that the reaching-and-grasping abilities of primates actually evolved before they learned to leap and before they developed stereoscopic, or 3D, vision.
Agents of evolutionary change
Isbell thinks proto-primates—the early mammals that eventually evolved into primates—were in better position compared to other mammals to evolve
specialized vision and enlarged brains because of the foods they ate.
"They were eating foods high in sugar, and glucose is required for metabolizing energy," Isbell said. "Vision is a part of the brain, and messing with the brain takes a lot of energy so you're going to need a diet that allows you to do that."
Modern primates are among the most frugivorous, or "fruit-loving," of all mammals, and this trend might have started with the proto-primates. "Today there are primates that focus on leaves and things like that, but the earliest primates may have had a generalized diet that included fruits, nectar, flowers and insects," she said.
Thus, early primates not only had a good incentive for developing better vision, they might have already been eating the high-energy foods needed to do so.
Testing the theory
Isbell says her theory can be tested. For example, scientists could look at whether primates can visually detect snakes more quickly or more reliably than other mammals. Scientists could also examine whether there are differences in the snake-detecting abilities of primates from around the world.
"You could see whether there is any difference between Malagasy lemurs, South American primates and the African and Asian primates," Isbell said.
Anthropologists have tended to stress things like hunting to explain the special adaptations of primates, and particularly humans, said Greene, the Cornell snake expert, but scientists are starting to warm to the idea that predators likely played a large role in human evolution as well.
"Getting away from things is a big deal, too," Greene said in a telephone interview.
If snake and primate history are as intimately connected as Isbell suggests, then it might account for other things as well, Greene added.
"Snakes and people have had a long history; it goes back to long before we were people in fact," he said. "That might sort of explain why we have such extreme attitudes towards snakes, varying from deification to "ophidiphobia," or fear of snakes.
- - - - -
http://www.nytimes.com/2013/10/31/science/afraid-of-snakes-your...
Afraid of Snakes? Your Pulvinar May
Be to Blame
By CARL ZIMMER
Published: October 31, 2013
This week in Proceedings of the National Academy
of Sciences, a team of scientists examines one
particularly long-lasting source of fear: snakes. The researchers found that certain neurons in the brain
only respond to these legless reptiles.
These snake-dedicated neurons, they argue, are a legacy of our distant primate past, when the animals posed one of the greatest threats to our survival.
The new study builds on years of experiments by psychologists. They found that the widespread fear of
snakes stems from a perceptual bias: people recognize snakes faster than other objects.
This bias toward snakes isn’t simply the result of learning to fear them.
Children recognize snakes just as quickly as adults. In a study published earlier this year in Developmental
Science, psychologists found no difference in the response to snakes when they compared children who grew up in cities with children who grew up in rural areas where they regularly encountered snakes.
Scientists find a similar bias among our primate cousins. In a 2009 study, for example, Japanese researchers showed macaque monkeys sets of pictures of snakes and flowers. In some trials, they
saw one snake amid eight flowers; in others, one flower amid eight snakes.
The monkeys got a reward — a squirt of juice — when they pointed to the oddball object. They consistently pointed to a snake faster than to a flower. Their swift response was particularly striking because they had never seen a live snake.
The fact that we share this bias toward snakes with
monkeys suggests that it evolved in our common ancestors. When primates evolved some 60 million years ago, they adapted to living in trees, searching for food at night and sleeping in the canopy during the day. Snakes creeping through those trees were among their deadliest enemies.
In her 2007 book “The Fruit, the Tree, and the Serpent: Why We See So Well,” Lynne A. Isbell, an anthropologist at the University of California at Davis, argued that a lot of the features that make primates unique evolved as defenses against snakes. Most importantly, the vision of primates became much more powerful so that they could detect snakes lurking in the foliage.
Recently, neuroscientists at the University of Toyama in Japan and the University of Brasilia in Brazil teamed up with Dr. Isbell to put her “Snake Detection Theory” to the test by examining a brain region known as the pulvinar. The neurons in the pulvinar receive signals from the eyes, and previous studies have suggested that they help to direct our attention quickly to particular objects in our view. People with damaged pulvinars can’t help but get distracted.
Other mammals have pulvinars, but the primate pulvinar is special. It contains extra clusters of neurons not found in other species. Dr. Isbell and her colleagues hypothesized that those extra neurons evolved specifically for recognizing snakes.
“I thought that region would be a likely place for finding neurons like this,” said Dr. Isbell.
The researchers threaded electrodes into the pulvinars of two macaque monkeys and then trained them to press a button each time they saw a picture. As the monkeys gazed at the pictures, the electrodes detected signals from the pulvinar. The researchers used the electrode recordings to decipher the individual behavior of 91 different neurons.
Some of the pictures they showed were of snakes. were of monkey faces, monkey hands and geometric shapes.
The scientists found that when they showed snakes to the monkeys, most of the 91 neurons fired strongly. At the sight of other pictures, they stayed quiet. The result was particularly striking given the fact that the monkeys had been raised at a primate facility where they probably had never before seen a snake.
“The research is very compelling,” said Vanessa LoBue, a Rutgers psychologist who studies fear of snakes in children.
But other experts weren’t yet ready to accept that the “snake neurons” were indeed exclusively responding to snakes.
They didn’t think the experiment could rule out the
possibility that the neurons fire in response to any enemy of the monkeys, like a leopard or an eagle.
“I would be much more convinced if they also tested photos of other known primate predators,” said Jason Kamilar of Arizona State University. Dr. Isbell and her colleagues are now running those tests.
Since humans have the same extra clusters of neurons in the pulvinar, Dr. Isbell and her colleagues predict that they are also snake-sensitive. But even if we have neurons dedicated to detecting snakes, that doesn’t mean that we have to be terrified of them. Once these neurons become active, they may trigger different responses, depending on our experiences with the serpentine world.
“People who like snakes are experiencing the same visual thing as people who hate snakes,” said Dr. Isbell.
- - - - -
Terry here: In addition to these interesting tidbits I recently read a paper that is to be published in one of the Neuroscience Journals that detailed some experiments where higher primates where exposed to snakes and to other primates being afraid of snakes.
It appears that most of us have a “switch” for Ophidiophobia. And for some of us simply seeing a snake will flip the switch. But seeing an adult primate respond with fear when exposed to a snake will almost always “flip the switch” in most young primates.
A primatologist (someone who studies primates, which includes humans, baboons, chimpanzees, gorillas orangutans, etc) used her 2-year-old child. The child was used to playing with some ‘tame’ chimps and when one of the adult chimps reacted badly (OK ‘freaked’) when a plastic snake was tossed in the play area, the child was terrified of snakes from then on.
What is interesting is that any adult primate can flip the switch for other juvenal primates. Such cross species interaction is kind of odd.
In my case my mother is terrified of snakes. Her mother was terrified of snakes. And yea I am terrified of snakes. When I was 21 a friend and I were climbing in the Red River Gorge nature preserve and we found a nice rattlesnake on a ledge about 100’ up. Now I am terrified of heights, but snakes outweigh heights. I stepped off the ledge without thinking, my friend grabbed my belt and said, “let’s make the snake fly” and used a long branch to pick Mr. Snake up and toss him off the edge. Phobias aren’t rational.
But humans and higher primates aren’t the only mammals who innately respond to ‘snakes’.
Of our house cats, who had never been outside, two “responded” to snakes.
Muffin, my wife’s first cat was a possible hybrid between a Wild/Bob cat and domestic cat, and when he first saw a plastic snake a friend brought me from the San Diego Zoo, he ‘freaked’. He swelled up to about 3 times his normal size and would run up and ‘whack’ the ‘snake’. After an hour or so he realized the snake wasn’t real and ignored it from then on.
We later were given a kitten (Shadow) that was too small to be away from his mother and after she got older I decided to see how she would respond to a snake.
And boy did she ‘respond’. She fluffed up and got between my wife and I and clearly was protecting us (wife and I) from the snake. Like Muffin, she would jump at the snake and hit it, she finally grabbed it behind the head and shook it like a rag doll. Unlike Muffin, she never ‘learned’ the snake wasn’t real. She also started hissing at and hitting my leather belt.
My wife was watching TV (Nature) and they had a show on about Cobras. When they showed a King Cobra both cats freaked and attacked the TV screen.
Shadow weighed about 4 pounds soaking wet as an adult. And it was almost funny to watch this small ball of fluff getting between us and a ‘snake’ to protect us.
Our third cat, Buttons, completely ignored snakes.
I even tested him with a real live Garter Snake and it was like, “Hey man, why are you bugging me?” Buttons was also the most laid back cat I ever met. I stepped on his tail one night and after about 5 minutes he ‘meowed’ at me as if to say, “Hey, goomer, get off my tail, please, when you feel like it, someday real soon now, if you really want to, if it isn’t to much trouble...”
- - - - - -
Desensitizing is an effective way for many people to overcome their fear of snakes, but it may not be effective for everyone. I have worked hard to overcome my fear with moderate success. But when I run into a snake when I don’t expect it, I still respond somewhat “negatively”.
“Respond somewhat “negatively”…..Yea, like jumping 10 feet away and cursing like a sailor.
Recently I have been working on our plumbing and I am more then terrified that I will meet Mr. Snake under our home. That would be a real bummer.
So if you are terrified of snakes, just remember we are hardwired to fear snakes.
And for those of you who aren’t afraid of snakes, be glad, and try not to laugh too hard at those of us who are afraid.
- - - - - -
As an undergrad I took a “civilian” survival course. And during an overnight survival “camp out” one student tossed a live snake on a coed student. The poor girl freaked, ran into a tree at “Warp 10” and suffered a mild concussion. So several of us gathered about 30 Garter Snakes and tossed them on his bed in the dorm room while he was asleep. Then we wedged the door so it wouldn’t open. The harder he pulled, the tighter the wedge blocked the door. Oh how sad. The guy was a “mess” the next day when we removed the wedge.
Mess is a polite word for raving madman…
I figured out which breaker supplied power to his room, and to wedge a door that opens inward requires some ingenuity. You fasten a wire to the wedge and pull it hard against the inside of the door as you close it. It was a bit more difficult to remove the wedge; I had to scrounge up a welding rod to push the wedge away from the bottom of the door.
Were we mean, and insensitive? Yea, so what! If you burn someone you should expect to get torched in response. I suspect Mr. Super Stud didn’t toss snakes on anyone else.
And yea, I am interested in way too many weird things…
Terry
I am sorry if I stepped on anyone’s toes. To me handling snakes to prove my faith is, er, silly.
Since I am the resident crank, er make that (pseudo)anthropologist I thought it might be interesting to discus why so many of us are terrified of snakes. After all understanding your fears is the first part of dealing with them. Unless you mess with snakes you stand almost no chance of getting bit. Many more people die from bee stings then snake bits. In Kentucky most of those who get bit with venomous snakes are drunk and playing with them. I have ran into venomous snakes in the wild about 5 times and as when I was younger I spent a lot of time in the woods in eastern Kentucky. And none of the encounters was especially dangerous.
The proper name for “fear of snakes” is Ophidiophobia.
As usual my ever so helpful comments will be in (), {}, or [].
- - - - - -
From http://www.pnas.org/content/early/2013/10/23/1312648110
Proceedings of the National Academy of Sciences
www.pnas.org
Pulvinar neurons reveal neurobiological evidence of past selection for rapid detection of snakes
Edited by David M. Hillis, University of Texas at Austin, Austin, TX, and approved October 1, 2013 (received for review July 4, 2013)
Significance
The present study shows preferential activity of neurons in the medial and dorsolateral pulvinar to
images of snakes. Pulvinar neurons responded faster and stronger to snake stimuli than to monkey faces, monkey hands, and geometric shapes, and were sensitive to unmodified and low-pass filtered images but not to high-pass filtered images. These results identify a neurobiological substrate for rapid detection of threatening visual stimuli in primates. Our findings are unique in providing neuroscientific evidence in support of the Snake Detection Theory, which posits that the threat of snakes strongly influenced the evolution of the primate brain. This finding may have great impact on our understanding of the evolution of primates.
Abstract
Snakes and their relationships with humans and other primates have attracted broad attention from multiple
fields of study, but not, surprisingly, from neuroscience, despite the involvement of the visual system and strong behavioral and physiological evidence that humans and other primates can detect snakes faster than innocuous objects. Here, we report the existence of neurons in the primate medial and dorsolateral pulvinar that respond selectively to visual images of snakes. Compared with three other categories of stimuli (monkey faces, monkey hands, and geometrical shapes), snakes elicited the strongest, fastest responses, and the responses were not reduced by low spatial filtering. These findings integrate neuroscience with evolutionary biology, anthropology, psychology, herpetology, and primatology by identifying a neurobiological basis for
primates’ heightened visual sensitivity to snakes, and adding a crucial component to the growing evolutionary perspective that snakes have long shaped our primate lineage.
- - - - -
(Don’t you love the things the government finds worthwhile to spend our precious money on.)
And
- - - - -
“Fear of snakes is one of the most common phobias, yet many people have never seen a snake in person.
“So how is this fear generated?
“New research suggests humans have evolved an
innate tendency to sense snakes — and spiders, too — and to learn to fear them.
“Psychologists found that both adults and children could detect images of snakes among a variety of non-threatening objects more quickly than they could pinpoint frogs, flowers or caterpillars. The researchers think this ability helped humans survive in the wild.
"The idea is that throughout evolutionary history, humans that learned quickly to fear snakes would have been at an advantage to survive and reproduce," said Vanessa LoBue, a post-doctoral fellow in psychology at the University of Virginia. "Humans who detected the presence of snakes very quickly would have been more likely to pass on their genes."
(In other words, those who weren’t afraid of snakes got bit and didn’t live to pass on those genes…)
“Previously, anthropologists have suggested the need to notice snakes in the wild may have led early primates to develop better vision and larger brains.
Eew!
The researchers were inspired to investigate the fear of snakes when they thought about how universally people dislike the slithering legless lizards.
"This feeling is really common," LoBue told LiveScience. "We don’t see snakes all the time. There's really no reason for this overwhelming disgust or hatred of snakes."
LoBue's collaborator, Judy DeLoache, a professor of psychology at the University of Virginia, happens to be petrified of snakes.
"I have almost a phobia of snakes," DeLoache said. "When I see a picture of a snake, I'm like, "Oh my God, eew! The reason we got into this research was
because I've always been fascinated by how it is that people develop it. My intuition was that there was something that made me feel afraid of snakes early on. You react to them very early on."
While babies and very young children do not usually fear snakes, they are unusually skilled at detecting them and show a predisposition to learn to fear snakes if they have bad experiences or even if they are exposed to negative portrayals of them in the media, the scientists found.
Spiders, too
To learn more, the psychologists showed adults and 3-year-old children images of a snake surrounded by objects of similar colors, such as frogs, caterpillars and flowers. Then they showed them pictures of a frog or a flower surrounded by snakes. Both groups were able to identify the hidden snake faster than the other hidden objects.
"We also did a study with spiders and found the same effect," LoBue said. Although the team has not tested other phobias, they don't think these predispositions would necessarily apply across the board.
"It would have to be something widespread, that you could encounter on a day-to-day basis," she said. "That’s why you don’t see lion and tiger and bear phobias as often. It would also have to be something that was around and dangerous while humans were evolving. Things that are dangerous right now, like guns, we haven’t had enough time to develop a predisposition to detect really quickly."
The results of the new study appear in the March 2008 issue of the journal, Psychological Science.
- - - - -
http://www.livescience.com/4183-fear-snakes-drove-pre-human-ev...
An evolutionary arms race between early snakes and mammals triggered the development of improved vision and large brains in primates, a radical new theory suggests.
The idea, proposed by Lynne Isbell, an anthropologist at the University of California, Davis, suggests that snakes and primates share a long and intimate history, one that forced both groups to evolve new
strategies as each attempted to gain the upper hand.
To avoid becoming snake food, early mammals had to develop ways to detect and avoid the reptiles before they could strike. Some animals evolved better
snake sniffers, while others developed immunities to serpent venom when it evolved. Early primates developed a better eye for color, detail and movement
and the ability to see in three dimensions—traits that are important for detecting threats at close range.
Humans are descended from those same primates.
Scientists had previously thought that these traits evolved together as primates used their hands and eyes to grab insects, or pick fruit or to swing through trees, but recent discoveries from neuroscience are casting doubt on these theories.
"Primates went a particular route," Isbell told LiveScience. "They focused on improving their vision to keep away from [snakes]. Other mammals couldn't do that. Primates had the pre-adaptations to go that way."
Harry Greene, an evolutionary biologist and snake expert at Cornell University in New York, says Isbell's new idea is very exciting.
"It strikes me as a very special piece of scholarship and I think it's going to provoke a lot of thought," Greene said.
Isbell's work is detailed in the July issue of the Journal of Human Evolution.
A new weapon
Fossil and DNA evidence suggests that the snakes were already around when the first mammals evolved some 100 million years ago. The reptiles were thus among the first serious predators mammals faced. Today, the only other threats faced by primates are raptors, such as eagles and hawks, and large carnivores, such as bears, large cats and wolves, but these animals evolved long after snakes.
Furthermore, these other predators can be safely detected from a distance. For snakes, the opposite is true.
"If you see them close to you, you still have time to avoid them," Isbell said. "Primate vision is particularly good at close range."
Early snakes killed their prey using surprise attacks and by suffocating them to death—the method of boa constrictors. But the improved vision of primates, combined with other snake-coping strategies developed by other animals, forced snakes to evolve a new weapon: venom. This important milestone in snake evolution occurred about 60 million years ago.
"The [snakes] had to do something to get better at finding their prey, so that's where venom comes in," Isbell said. "The snakes upped the ante and then the
primates had to respond by developing even better vision."
Once primates developed specialized vision and enlarged brains, these traits became useful for other purposes, such as social interactions in groups.
Seeing in 3D
Isbell's new theory could explain how a number of primate-defining traits evolved.
For example, primates are among the few animals whose eyes face forward (most animals have eyes located on the sides of their heads). This so-called
"orbital convergence" improves depth perception and allows monkeys and apes, including humans, to see in three dimensions. Primates also have better color vision than most animals and are also unique in relying heavily on vision when reaching and grasping for objects.
One of the most popular ideas for explaining how these traits evolved is called the "visual predation hypothesis." It proposes that our early ancestors were
small, insect eating mammals and that the need to stalk and grab insects at close range was the driving force behind the evolution of improved vision.
Another popular idea, called the "leaping hypothesis," argues that orbital convergence is not only important for 3D vision, but also for breaking through camouflage. Thus, it would have been useful not only for capturing insects and finding small fruits, but also for aiming at small, hard-to-see branches during
mid-leaps through trees.
But there are problems with both hypotheses, Isbell says.
First, there is no solid evidence that early primates were committed insectivores. It's possible that like many primates today, they were generalists, eating a variety of plant foods, such as leaves, fruit and nectar, as well as insects.
More importantly, recent neuroscience studies do not support the idea that vision evolved alongside the ability to reach and grasp. Rather, the data suggest that the reaching-and-grasping abilities of primates actually evolved before they learned to leap and before they developed stereoscopic, or 3D, vision.
Agents of evolutionary change
Isbell thinks proto-primates—the early mammals that eventually evolved into primates—were in better position compared to other mammals to evolve
specialized vision and enlarged brains because of the foods they ate.
"They were eating foods high in sugar, and glucose is required for metabolizing energy," Isbell said. "Vision is a part of the brain, and messing with the brain takes a lot of energy so you're going to need a diet that allows you to do that."
Modern primates are among the most frugivorous, or "fruit-loving," of all mammals, and this trend might have started with the proto-primates. "Today there are primates that focus on leaves and things like that, but the earliest primates may have had a generalized diet that included fruits, nectar, flowers and insects," she said.
Thus, early primates not only had a good incentive for developing better vision, they might have already been eating the high-energy foods needed to do so.
Testing the theory
Isbell says her theory can be tested. For example, scientists could look at whether primates can visually detect snakes more quickly or more reliably than other mammals. Scientists could also examine whether there are differences in the snake-detecting abilities of primates from around the world.
"You could see whether there is any difference between Malagasy lemurs, South American primates and the African and Asian primates," Isbell said.
Anthropologists have tended to stress things like hunting to explain the special adaptations of primates, and particularly humans, said Greene, the Cornell snake expert, but scientists are starting to warm to the idea that predators likely played a large role in human evolution as well.
"Getting away from things is a big deal, too," Greene said in a telephone interview.
If snake and primate history are as intimately connected as Isbell suggests, then it might account for other things as well, Greene added.
"Snakes and people have had a long history; it goes back to long before we were people in fact," he said. "That might sort of explain why we have such extreme attitudes towards snakes, varying from deification to "ophidiphobia," or fear of snakes.
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http://www.nytimes.com/2013/10/31/science/afraid-of-snakes-your...
Afraid of Snakes? Your Pulvinar May
Be to Blame
By CARL ZIMMER
Published: October 31, 2013
This week in Proceedings of the National Academy
of Sciences, a team of scientists examines one
particularly long-lasting source of fear: snakes. The researchers found that certain neurons in the brain
only respond to these legless reptiles.
These snake-dedicated neurons, they argue, are a legacy of our distant primate past, when the animals posed one of the greatest threats to our survival.
The new study builds on years of experiments by psychologists. They found that the widespread fear of
snakes stems from a perceptual bias: people recognize snakes faster than other objects.
This bias toward snakes isn’t simply the result of learning to fear them.
Children recognize snakes just as quickly as adults. In a study published earlier this year in Developmental
Science, psychologists found no difference in the response to snakes when they compared children who grew up in cities with children who grew up in rural areas where they regularly encountered snakes.
Scientists find a similar bias among our primate cousins. In a 2009 study, for example, Japanese researchers showed macaque monkeys sets of pictures of snakes and flowers. In some trials, they
saw one snake amid eight flowers; in others, one flower amid eight snakes.
The monkeys got a reward — a squirt of juice — when they pointed to the oddball object. They consistently pointed to a snake faster than to a flower. Their swift response was particularly striking because they had never seen a live snake.
The fact that we share this bias toward snakes with
monkeys suggests that it evolved in our common ancestors. When primates evolved some 60 million years ago, they adapted to living in trees, searching for food at night and sleeping in the canopy during the day. Snakes creeping through those trees were among their deadliest enemies.
In her 2007 book “The Fruit, the Tree, and the Serpent: Why We See So Well,” Lynne A. Isbell, an anthropologist at the University of California at Davis, argued that a lot of the features that make primates unique evolved as defenses against snakes. Most importantly, the vision of primates became much more powerful so that they could detect snakes lurking in the foliage.
Recently, neuroscientists at the University of Toyama in Japan and the University of Brasilia in Brazil teamed up with Dr. Isbell to put her “Snake Detection Theory” to the test by examining a brain region known as the pulvinar. The neurons in the pulvinar receive signals from the eyes, and previous studies have suggested that they help to direct our attention quickly to particular objects in our view. People with damaged pulvinars can’t help but get distracted.
Other mammals have pulvinars, but the primate pulvinar is special. It contains extra clusters of neurons not found in other species. Dr. Isbell and her colleagues hypothesized that those extra neurons evolved specifically for recognizing snakes.
“I thought that region would be a likely place for finding neurons like this,” said Dr. Isbell.
The researchers threaded electrodes into the pulvinars of two macaque monkeys and then trained them to press a button each time they saw a picture. As the monkeys gazed at the pictures, the electrodes detected signals from the pulvinar. The researchers used the electrode recordings to decipher the individual behavior of 91 different neurons.
Some of the pictures they showed were of snakes. were of monkey faces, monkey hands and geometric shapes.
The scientists found that when they showed snakes to the monkeys, most of the 91 neurons fired strongly. At the sight of other pictures, they stayed quiet. The result was particularly striking given the fact that the monkeys had been raised at a primate facility where they probably had never before seen a snake.
“The research is very compelling,” said Vanessa LoBue, a Rutgers psychologist who studies fear of snakes in children.
But other experts weren’t yet ready to accept that the “snake neurons” were indeed exclusively responding to snakes.
They didn’t think the experiment could rule out the
possibility that the neurons fire in response to any enemy of the monkeys, like a leopard or an eagle.
“I would be much more convinced if they also tested photos of other known primate predators,” said Jason Kamilar of Arizona State University. Dr. Isbell and her colleagues are now running those tests.
Since humans have the same extra clusters of neurons in the pulvinar, Dr. Isbell and her colleagues predict that they are also snake-sensitive. But even if we have neurons dedicated to detecting snakes, that doesn’t mean that we have to be terrified of them. Once these neurons become active, they may trigger different responses, depending on our experiences with the serpentine world.
“People who like snakes are experiencing the same visual thing as people who hate snakes,” said Dr. Isbell.
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Terry here: In addition to these interesting tidbits I recently read a paper that is to be published in one of the Neuroscience Journals that detailed some experiments where higher primates where exposed to snakes and to other primates being afraid of snakes.
It appears that most of us have a “switch” for Ophidiophobia. And for some of us simply seeing a snake will flip the switch. But seeing an adult primate respond with fear when exposed to a snake will almost always “flip the switch” in most young primates.
A primatologist (someone who studies primates, which includes humans, baboons, chimpanzees, gorillas orangutans, etc) used her 2-year-old child. The child was used to playing with some ‘tame’ chimps and when one of the adult chimps reacted badly (OK ‘freaked’) when a plastic snake was tossed in the play area, the child was terrified of snakes from then on.
What is interesting is that any adult primate can flip the switch for other juvenal primates. Such cross species interaction is kind of odd.
In my case my mother is terrified of snakes. Her mother was terrified of snakes. And yea I am terrified of snakes. When I was 21 a friend and I were climbing in the Red River Gorge nature preserve and we found a nice rattlesnake on a ledge about 100’ up. Now I am terrified of heights, but snakes outweigh heights. I stepped off the ledge without thinking, my friend grabbed my belt and said, “let’s make the snake fly” and used a long branch to pick Mr. Snake up and toss him off the edge. Phobias aren’t rational.
But humans and higher primates aren’t the only mammals who innately respond to ‘snakes’.
Of our house cats, who had never been outside, two “responded” to snakes.
Muffin, my wife’s first cat was a possible hybrid between a Wild/Bob cat and domestic cat, and when he first saw a plastic snake a friend brought me from the San Diego Zoo, he ‘freaked’. He swelled up to about 3 times his normal size and would run up and ‘whack’ the ‘snake’. After an hour or so he realized the snake wasn’t real and ignored it from then on.
We later were given a kitten (Shadow) that was too small to be away from his mother and after she got older I decided to see how she would respond to a snake.
And boy did she ‘respond’. She fluffed up and got between my wife and I and clearly was protecting us (wife and I) from the snake. Like Muffin, she would jump at the snake and hit it, she finally grabbed it behind the head and shook it like a rag doll. Unlike Muffin, she never ‘learned’ the snake wasn’t real. She also started hissing at and hitting my leather belt.
My wife was watching TV (Nature) and they had a show on about Cobras. When they showed a King Cobra both cats freaked and attacked the TV screen.
Shadow weighed about 4 pounds soaking wet as an adult. And it was almost funny to watch this small ball of fluff getting between us and a ‘snake’ to protect us.
Our third cat, Buttons, completely ignored snakes.
I even tested him with a real live Garter Snake and it was like, “Hey man, why are you bugging me?” Buttons was also the most laid back cat I ever met. I stepped on his tail one night and after about 5 minutes he ‘meowed’ at me as if to say, “Hey, goomer, get off my tail, please, when you feel like it, someday real soon now, if you really want to, if it isn’t to much trouble...”
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Desensitizing is an effective way for many people to overcome their fear of snakes, but it may not be effective for everyone. I have worked hard to overcome my fear with moderate success. But when I run into a snake when I don’t expect it, I still respond somewhat “negatively”.
“Respond somewhat “negatively”…..Yea, like jumping 10 feet away and cursing like a sailor.
Recently I have been working on our plumbing and I am more then terrified that I will meet Mr. Snake under our home. That would be a real bummer.
So if you are terrified of snakes, just remember we are hardwired to fear snakes.
And for those of you who aren’t afraid of snakes, be glad, and try not to laugh too hard at those of us who are afraid.
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As an undergrad I took a “civilian” survival course. And during an overnight survival “camp out” one student tossed a live snake on a coed student. The poor girl freaked, ran into a tree at “Warp 10” and suffered a mild concussion. So several of us gathered about 30 Garter Snakes and tossed them on his bed in the dorm room while he was asleep. Then we wedged the door so it wouldn’t open. The harder he pulled, the tighter the wedge blocked the door. Oh how sad. The guy was a “mess” the next day when we removed the wedge.
Mess is a polite word for raving madman…
I figured out which breaker supplied power to his room, and to wedge a door that opens inward requires some ingenuity. You fasten a wire to the wedge and pull it hard against the inside of the door as you close it. It was a bit more difficult to remove the wedge; I had to scrounge up a welding rod to push the wedge away from the bottom of the door.
Were we mean, and insensitive? Yea, so what! If you burn someone you should expect to get torched in response. I suspect Mr. Super Stud didn’t toss snakes on anyone else.
And yea, I am interested in way too many weird things…
Terry
