Primates And Snakes: 75 Million Years of Deadly Dialogue?
Thumbnail image: David Clode
[Slide text: Primates & Snakes: 75 Million Years of Deadly Dialog?
Harry W. Greene, Museum of Vertebrates, Department of Ecology & Evolutionary Biology, Cornell University; Photos: Bonnet macaque looking at 4 m king cobra, and sculpture Serpent Devouring a Human Figure, circa 11th-17th century, terracotta- Undetermined Inland Niger Delta Peoples, Djenne Region, Mali]
[Miyoko] We’ll start in just a minute, we’re waiting for the live. So good evening, my name is Miyoko Chu, I’m senior director of communications here at the Lab, and I want to thank all of you in the room for joining us, and also all of you on the live stream.
I want to start with an announcement about the next week’s seminar, which is hosted by the Cayuga Bird Club. We’ll be here next Monday night, the 11th, the same time, 7:30 club business begins, and the talk will follow up business. It’s about Patagonia, natural history of Patagonia. It’s next week.
So tonight we’re gonna broaden our perspective a bit, for a topic on primates and snakes, 75 million years of deadly dialog. Our speaker is Dr. Harry Greene, who began his career as an army medic, before earning his master’s degree from the University of Texas at Arlington and PhD from the University of Tennessee.
For two decades he was professor and curator in Berkeley’s Museum of Vertebrate Zoology, and it was there that I met him as a graduate student and I was fortunate that he became an advisor on my dissertation committee. It was also fortunate that we both ended up coming to Cornell, through separate routes, and today Harry is professor emeritus of ecology and evolutionary biology here at Cornell.
His honors include UC Berkeley’s Distinguished Teaching Award, the Edward O. Wilson Naturalist Award, President of the American Society of Ichthyologists and Herpetologists, and Cornell’s Stephen H. Weiss Presidential Fellowship.
In 2014 Business Insider named him one of Cornell’s top ten professors, and he was elected to the American Academy of Arts and Sciences. His book Snakes: the Evolution of Mystery in Nature won a PEN Literary Award, garnered a two-page spread in Time magazine, and made the New York Times’ annual list of 100 Most Notable Books, too.
He is also author of the evocative book Tracks and Shadows: Field Biology as Art.
So welcome Harry, thanks for giving us a talk tonight.
[Harry] Thanks, Miyoko.
[Harry] Thanks very much. Thanks for coming out. It’s always a pleasure to be here. I’m a little sad that this isn’t Cayuga Bird night, I I thought it might be, and the one other time I spoke here, I didn’t know that at the start they read the entire list of the birds of the basin
and people shout out if they’d seen it. And so I was looking forward tonight to getting up and saying spring peeper, milk snake.
[Laughter] And so, so we’ll get on with it.
[Audience] You didn’t really see all of those this month?
[Harry] No, I actually haven’t seen any of them this month. I’ve only seen birds and mammals this month.
So we are going to talk about something a little different, and I’m going to tell you how I got there. In 1997 I published this book on snakes
[Slide text: Monkeys, snakes, and spears… -treeshrews & colugos, lemurs, tarsiers, OW & NW monkeys, & apes kill &/or are killed by snakes -Reticulated Pythons killed 6 Agta, 26% of males had survived attacks; hunted pythons, & monkeys; Photos: Tarsier eating venomous coralsnake and python (6.9 m, ~75 kg) held by two Agta men (~1.4 m, ~45 kg)]
and in the course of writing Snakes I reviewed most of the natural history literature globally on snakes. And I encountered what I thought was a fascinating pattern. That is I found records in the natural history literature of every major lineage of primates, that is to say lemurs, tarsiers, new world primates, old world primates, and so forth. Every major lineage of primates, both killing and being killed by snakes.
And because I knew that snakes are older than primates, it set in my mind the idea that perhaps we, snakes have been a problem for us for their entire, the entire history of primates, which is about 65 to 80 million years.
I also was fascinated by the fact that this wasn’t a one-way relationship, that in fact it seemed to be incredibly polarized. I wasn’t so surprised that people don’t like snakes, and that people want to kill snakes, and even that other primates want to kill snakes. What really kind of fascinated me was that there are also groups of people that deify snakes.
There are people like me that as as tiny children are fascinated from the get-go, whereas other people have these extreme phobias. And you know there are people that could not be in this room tonight, they could not look at that picture. I know someone who prefers that you never say the word snake around them. I know someone who cut the word S-N-A-K-E, which she will not say, out of every book in her library.
So it can be really extreme, it’s a true phobia. And because I’m arachnophobic myself, and acrophobic myself, I sympathize with this, I’m just not phobic of snakes.
So that’s how it started. Then I got here in 1999 and in the first herpetology course I taught was a woman named Amber Wright who’s now a professor at the University of Hawaii, and at graduation that year Amber’s father came up to me, he’s a geographer named Tim Wright, a Cornell graduate as it happens. And he gave me a thirty-year weathered print of this picture you’re looking at on the right of the two Agta Negritos in northern Luzon in the Philippines in the late 1960s with a 25-foot female reticulated python they’d just killed and are about to butcher and eat.
This, this photograph dropped my jaw, I mean, I I just found it extraordinary to look at it. It took some, it took some detective work, but I tracked down the original photographer, a man named Tom Headland. And it turned out that Tom, who works for the Summer Institute of Linguistics in Dallas, had done his PhD work in the Philippines studying the Agta Negritos.
And he learned their language when they were still preliterate, nomadic hunter-gatherers that lived in little temporary shelters. He hunted with them, he did what ethnographers call focal sampling, where he walks along behind them, writes down everything they do, and so forth.
And because I thought I want to use this photograph in a book someday I tracked him down, and asked his permission. In our conversation he said, “You know, I’ve got a folder of data that I wonder if you’d be interested in.” And he said, “I interviewed 120 Agta ethnographically,” that is to say tried to ask them unbiased questions, “and I found out that 26% of the adult males had survived feeding attacks by reticulated pythons.”
And I just, I couldn’t believe it. I mean just, it’s extraordinarily rare to have information on the actual incidence of predation and attempted predation on humans living a hunter-gatherer lifestyle in in this, in this time. I mean it’s really extremely unusual. So I, so one thing led to another and we published this information.
It turned out that 26 percent of the adult males had survived predatory attacks by these giant pythons. In the collective memory of the 120 Agta that Tom interviewed there were six fatalities from the pythons, including two children that were eaten while he was living with the group.
It turned out that the Agta mainly hunt deer, pigs, and monkeys. And they eat the pythons opportunistically. When they butcher the pythons they sometimes find in the stomachs of the pythons the same three species that they concentrate on, the Philippine deer, pig, and macaque, a monkey.
So the Agta and the reticulated pythons are simultaneously predators, prey, and ecological competitors. They’re preying on each other, and they’re also competing for the same prey. I mean, what a relationship.
[Harry] Where do they live? Well they live in northern Luzon in the Philippine Islands.
Okay. And a big adult male Agta weighs about 90 pounds. So I think in fact that female reticulated python could easily have eaten both those men if she’d gotten a drop on them.
[Harry] What did the python weigh? She weighed I believe about a hundred and fifty-five pounds. And if you look at the size of her head, I’m going to tell you a little bit more about how snakes can eat big meals in a second, but trust me for now I think she could have easily consumed those men without any difficulty, so.
It’s commonly stated by herpetologists that there aren’t snakes big enough to eat adult humans, but these adult humans that are speaking are always male Caucasians, and in fact the places where big snakes live, adults are easily consumable by big snakes.
So I found not only these major lineages of primates, but also treeshrews and flying lemurs, or as they’re now called colugos, the closest living relatives of primates. I had these records of all these lineages eating each other, and so that led to this idea. And I pursued it, and in fact I’m writing a book now called Monkeys, Snakes, and Spears, which started out to be about hunting in snakes and primates, and it’s turned out to be maybe more about the notion of wildness, and maybe I can talk about that a little bit at the end.
[Slide text: The Snake Detection Theory…; Images: Primate phylogenetic tree, photo of snake head, and photo of southern African python (~3 m, ~8 kg) around a vervet monkey (~4)]
In the meantime in 2009 Lynne Isbell, who’s a primatologist behaviorist at UC Davis, published a book from Harvard University Press called the tree, The Tree, the Flower, and the Serpent: Why We See So Well. And Lynne accomplished an amazing synthesis of the neurobiology of vision in primates, the evolution of primates, the evolution of snakes.
And she came up with what she calls the snake detection theory. It has two parts, and I’ll just tell you it in brief, and then we’re gonna sort of work through it for the next 30, 40 minutes and I’ll show you examples of all this.
The first part though is that when primates arose, when they evolved from a treeshrew-like ancestor, something like 75 million years ago, there were already waiting, so to speak, constricting snakes big enough to kill them and eat them. So snakes, hidden snakes, hard to see, extremely dangerous snakes, were a threat from the get-go.
And Lynne hypothesized that some of the specializations of primates that I’ll tell you about in just a second are in fact adaptations for overcoming this threat of snakes. It turns out that within primates there’s sort of a second wave of this improvement on the neurobiology of vision, and of spotting snakes. And it happens at the level of what are called anthropoids. And the anthropoids are the old and new world monkeys, and us.
Okay, so there’s this two-step theory. One having to do with the origin of primates, one having to do with the origin of the anthropoids.
I just want to say one more thing about this photograph you’re looking at. That’s a southern African python, not a large one, it’s about ten feet long. It’s just killed and is about to consume a vervet. And I think most people even some people who have pet snakes might think that looks like an extraordinarily large meal. That’s not an extraordinarily large meal for a snake. That’s kind of an average big meal for a snake. It’s a bit less than 50% of the, maybe right at 50% of the body mass of the snake, that’s not what I call a huge meal for a snake, but you might think it’s a big meal.
[Slide text: Primates vs. Treeshrews & colugos… -Flexible shoulders, grasping hands & feet -Bigger brains -Orbital convergence -Vision-controlled grasping (unlike rodents) -Snake-specific recognition mechanisms, some pre-conscious -Enhanced in monkeys & apes; Image: Drawing of python and vervet monkey’s head, with pre-conscious and conscious pathways shown in the monkey]
Okay, so what about specializations of primates? Well it turns out when you compare primates to their closest living relatives the treeshrews and the flying lemurs, we have more flexible shoulders, grasping hands and feet, we have bigger brains, and of course brains evolve to even larger sizes within the group primates. We have orbital convergence, which means our eyes tend to be like this for stereoscopic vision, give us good distance vision and so forth.
We have vision-controlled grasping, so it turns out when you see a squirrel pick up a nut and raise it to its mouth, it’s mainly using olfactory cues to guide its hands, not visual cues. But we primates use visual cues to guide things to our hands. We’re, we are perhaps above all else super visual, super manually dexterous, and super smart.
Now it turns out we have snake recognition mechanisms. They are present at a certain level as far as we know through all primates. Some of them are what are called pre-conscious mechanisms, so they actually happen before we’re even aware of them. Some of them are conscious mechanisms. Uh I won’t take time to go into all this partly because I’m not a neurobiologist, but when you’re looking at that graphic of the monkey’s head, and the red and blue arrows, we’re talking about neural pathways that goes from the eyes to the processing centers, and from the processing centers to the fear center in the amygdala and so forth.
So there’s, there are these recognition mechanisms I’ll elaborate on that in just a moment. And it’s these, these recognition mechanisms and their connections to the fear module in the brain and so forth that get even better in our special group the anthropoids.
[Slide text: Some pulvinar neurons respond more strongly to snakes than other images; Graph: Response magnitude (spike/second/trial) of photos of various snakes, primates, and symbols, Le et al. 2013, PNAS]
So what am I talking about? Well one way you can look at this is to record from individual neurons. Okay, so these, this is the result of study in which individual pulvinar, that’s one of the processing centers in the thalamus part of the brain, are exposed, the monkey is exposed to various photographs while they’re recording from these individual neurons.
So you can see the hugely greater responses on the left to pictures of snakes compared to pictures of monkey faces and various other kinds of objects and figures.
[Slide text: Snakes found more quickly than spiders under “challenging attentional conditions”; Photos: Child and monkey touching images on computer screens; Graph: Exposure duration versus reaction time to snake, spider, and mushroom, Soares et al. 2014, PLoS One]
Another way you can do this with intact animals, that is to say without recording from nerves, is to offer a challenge, a task, that you get rewarded for participating in. So it turns out with both children and with captive monkeys you can offer them the problem of distinguishing something in particular, say a snake, a spider, or a mushroom, from an array of photographs of various things that include that object that you’ve asked them to find. And a challenging attentional condition is you only get 1/3 of a second to make the distinction, or you only get a half second, or you get about a second, okay.
So it turns out if you do that and give a child or a monkey about a second, 1200 milliseconds, just over a second, there’s no difference in our ability to distinguish or to pick out mushroom, snake, or spider. If you cut it down to about half a second, mushrooms are out.
If you cut it down to three hundred milliseconds, about a third of a second or less we can still pick snakes out from an array of other objects, but not even spiders let alone mushrooms. These are examples of neurobiological mechanisms for recognition, and I want to stress that I haven’t said fear, okay. And actually I would say we don’t yet know just how fear gets coupled to all these recognition mechanisms in the life of an individual primate, be it either a monkey or a person, let alone within a particular culture of primates and so forth. Yes?
[Harry] Yes, right. So do I need, should I repeat the question? Okay, so what Karen asked is what’s the actual task in the lower left hand picture here? What’s, what the monkey has been trained to do is to look at an image, and then look at a set of nine images, and pick out that image, that kind of thing from the nine possibilities, okay. And it turns out that if you give us a second, and the monkey gets rewarded. So the monkey quickly learns, as does the child, that okay here’s your task for today, here’s a little game we’re gonna play. You do your part, you get a treat. Okay, does that help? Okay.
[Slide text: ~200 observation of 7 families, 22 genera, & 32 snake species versus 5 families, 37 genera, & 50 treeshrew, colugo, & primate species… 10 constricting species eat primates
16 rear- or front-fanged species kill primates
15 species are mobbed or otherwise hasseled by primates; Photo: Two men sitting near and photographing a large snake]
Okay, so for my part what I’ve continued to do is search the literature for additional observations of primates and snakes. And I actually go to primatology conferences now, I go to the American Association of Physical Anthropologists meeting every spring. And whereas most of the people there are going to the posters and the talks, and really interested in the particular subject that’s being studied, I go up to these people, I go, “It’s not that I’m not interested in what you do, but what I’d really like to know is do you have any unpublished observations of snakes and monkeys interacting?”
And so I’ve, I’ve just relentlessly sifted the world’s primatologists for observations, I’ve come up with many fascinating anecdotes as a result. So we now have, just to sort of summarize, we have observations of about 25 or 30 species of monkeys killing snakes of various kinds, and we have about 25 or 30 species that in some way or another are being damaged by snakes.
[Slide text: Snake Detection Theory, part 1: Big-mouthed basal serpents constrict(ed) & consume(d) heavy* bulky prey *up to ~100% of snake’s mass; Images: Snake phylogenetic tree and primate phylogenetic tree, and photo of boa constrictor (~3 m, ~10 kg) killing white-tailed deer (~4 kg)]
So, now let’s look at this a little more detail. Let’s talk about the first part of the snake detection theory, and that involves what we call the big mouthed ancestral serpents. So on the left there you’re looking at a photograph from Guanacaste, Costa Rica of about a ten-foot boa constrictor consuming a white-tailed deer fawn. And once again I mean I think most people would look at this and say that is a gigantic meal.
In fact I’ve seen the photographs that were taken after the snake finished swallowing the deer, and it doesn’t look like the Little Prince, so it doesn’t look like, like that okay, it looks like a, an unusually heavy bodied boa constrictor. So again this is, this is like an average big meal for a snake, this is not a huge big meal for a snake.
That deer probably weighed maybe mmm forty, fifty percent of the body mass of that snake. Our biggest records for boas and pythons are of them consuming things that weigh right at a hundred percent of their own mass, okay.
So it’s a big deal. And the snakes that had the jaw apparatus to do that were around when primates arose.
[Slide text: Reticulated Pythons eat… Sunda Colugos, Horsfield’s & Large Treeshrews, Slender Lorises, Spectral Tarsiers, Long-tailed Macaques, Sumatran & Silvery Langurs, Siamangs, Sumatran Orangs, Human hunter-gatherers; Photos: Reticulated python radiograph showing two juvenile macaques inside it, and dead reticulated python with stomach cut open to show mother and baby macaque inside]
Just to give you a little flavor of what’s going on, it turns out on now every one of the major land masses except Australia and the polar masses there is at least one snake that regularly eats primates. So there’s no snake that specializes in primates, but in each of the major continental tropical continents there’s a snake that regularly eats them.
And just as an example, reticulated pythons, which are one of the two largest snakes in the world. They, these are just the species we have records of them eating. The flying lemur, two species of treeshrews, lorises, tarsiers, several kinds of macaques and langurs, siamangs, which are a gibbon relative, Sumatran orangs, and human hunter-gatherers.
The picture you’re looking at in the upper right is of a small reticulated python in Singapore. It’s been radiographed and has eaten two juvenile macaques. So you can see the sort of hollow orbits of the skulls maybe looking out from the radiograph. In the lower right is a reticulated python that was killed and opened up, and it consumed a macaque and her nursing offspring at the same time. So that’s the huddled up macaque and her offspring sort of sitting on her head there inside the stomach of the, of the reticulated python.
So an individual reticulated python, these are snakes that live for decades, an individual reticulated python during its life depending on where it’s lived might eat all those things, okay. Along with various deer and rats and all kinds of other things.
[Slide text: Madagascan boas and rear-fanged snakes eat… Eastern & Southern Lesser Bamboo Lemurs, Coquerel’s Sifakas, Common Brown Lemurs, Gray Mouse Lemurs; Photos: Madagascan Ground Boa (2.7 m, 8.2 kg) wrapped around Common Brown Lemur (~2.5 kg), and Coquerel’s Sifaka (~4 kg) hanging from a tree branch]
Madagascar has several species of boas, no dangerously venomous snakes, but several species of boas. And all of them eat lemurs. This is a particularly interesting case, the photograph you’re looking at on the left. This is the largest boa ever measured in Madagascar. His name was, her name I think was a female based on size, is Big George. Big George lived on the grounds of an eco-tourism resort for about a decade, and was regularly seen by the workers and by visitors eating lemurs.
So in this photograph you’re seeing Big George swallowing a brown lemur, okay. Now Big George met her match when one day in view of some workers she ambushed the fourth Coquerel’s sifaka lemur of a troop of eight marching down a path. So there’s eight sifakas marching down this path through the grass, Big George is lying in ambush. Big George makes a judgment based on odor, size, whatever that this is an appropriate prey item. Strikes, hits the fourth, which happens to be a pregnant female, and before Big George can successfully dispatch that female sifaka the other seven jump on Big George and proceed to just beat her up. And in the course of this beating the original victim manages to free herself and bite Big George on the head. All the sifakas escape, two months later Big George dies of starvation from a broken jaw, and the sifaka gives birth to a normal baby.
So it’s a, I think it’s a fascinating case history because it shows you how Big George had an appropriate, you know, notion of what’s, what’s, what’s a prey item that I can take, that I can handle. What Big George couldn’t account for was a social primate that was capable of socially protecting itself.
[Slide text: “Disjoint”? “Unhinge”? NOOOOOOOO!! Joe Furman’s “Can snakes unhinge their jaws?” http://www.youtube.com/watch?v=Mm9h6KE-ZOk; Images: Diagram and photo of snake jaws, and Harry and two kids with their arms out]
Okay, so I don’t have time tonight to really go into detail about how it is a snake can eat such a big meal. If you’d like to know more about it you can look up Joe Furman’s YouTube video on this. A lot, actually Anne James who was in my class back in the ’90s in Berkeley will remember this. I made up this little way of explaining how a snake’s head works. Making your own body into a model, and the arms are the lower jaws and so on.
And I could never figure out how to make upper jaws with just two arms, and so I went to this high, this elementary school in Houston, and I got my friend Joe Furman’s daughter and her classmates to help me figure out how to do a better job of teaching this. And it turns out it involved two kids, one being the upper jaw, one be the lower jaw.
But in a nutshell, snakes have highly mobile jaws including not just their lower jaws, which are not connected in the front, but also their upper jaws, which consists of two rows of teeth on each side and can move back and forth.
And basically a snake eats such huge things not by pulling food into its mouth but by walking its mouth, by walking its mouth around a food item, okay. That’s what happens.
Now the reason this is important here has to do with this, I’m gonna try using the little pointer here because of the people watching the video.
Can you see the little pointer moving?
[Harry] Okay, here’s a boa skull. Here’s the right upper jaw, and this is the right upper jaw viewed from below. Does that make sense? So now we’re down below looking up at this. And you see this inner row of teeth, and this outer row of teeth. Well that matters because
[Slide text: Maxillary liberation & front-fangs (≥3X, ~700 species); Images: Diagram of snake jaws, photo of snake with mouth open and fang highlighted in a box, photo of snake with fangs visible eating a frog, and phylogenetic tree of snakes showing front-fangs >50 mya]
about 55 to 65 million years ago snakes invented something new. And that was a way to use that outer row of teeth for other things. They basically freed that outer row up for all kinds of inventions. And as a result three times in the evolutionary history of snakes, they invented front-fangs, okay.
Before they had all these teeth that were solid, used for pulling their head over the food. Now they invented, on the outer row, on the outer bone of each upper jaw. Instead of having a row of teeth they just had one big, hollow tooth. And you see that in cobras and their relatives, and vipers, and in a somewhat obscure group of African snakes that invented it the third time.
All that happened around 55 to 65 million years ago. And it just opened up whole new ways of life for snakes.
[Slide text: Very heavy bulky prey* —tranquilized & tenderized! *up to 160% of snake’s mass; Photos: Three vipers eating large prey items, including a black-tailed rattlesnake eating a desert cottontail]
One of the things we’re sure it did was make it possible for them to eat even bigger food items. And probably the reason for this is that first of all by being able to rapidly inject this cocktail of immobilizing and digestive enzymes they could kill things that they couldn’t otherwise kill. But the other thing is by being able to inject this cocktail of digestive enzymes they could digest a huge item from the inside out before it rotted from the outside in.
Okay so these are all vipers in these pictures. The one in the middle is a black-tailed rattlesnake that’s just finishing swallowing a desert cottontail, okay. The way it worked is that that black-tailed rattlesnake laid in ambush, struck that cottontail, released in a few hundred milliseconds the cottontail, thereby freeing itself from any risk. The cottontail loped away. We once watched a cottontail run 90 yards after being struck by a rattlesnake.
The viper then tracks the prey. By the time it gets there the prey’s dead and digesting from the inside out, and the viper swallows it, okay. It’s a fantastic thing, and we were satisfied that the historical original adaptive significance of the invention of front-fangs had to do with feeding.
[Slide text: Front-fanged snakes threaten & punish—but whom are they teaching?; Photos: Rattlesnake striking a mouse, cobra with head raised and hood out, rattlesnake rattling, coral snake with bright colors, and saw-scaled viper poised to strike; Image: Phylogenetic tree of snakes showing front-fangs >50 mya]
But it also turns out, and this is something we just began to think about recently, is that it does something else for these front-fanged snakes. And this will only be intuitively obvious to you if you’ve ever been bitten by non-venomous snakes, but if you get bitten by a garter snake, or a water snake, or it’ll be more impressive if it’s a boa or python.
Snake teeth are recurved, and they’re designed for hanging on. So if you get bitten defensively by one of these northern water snakes in Beebe Lake, it’s not like it’ll just be like this, it’ll probably leave some scrap, scratch, scratches as it pulls off. The snake has to disengage itself, and those are seconds that are extremely risky for the snake, okay.
I think most snakes would rather so to speak not bite you, because they’d like to not be tangled up with you physically. And what front-fangs did is make it possible for almost instantaneous, incredible punishment, okay. So on the left there you’re looking at some video frames from high-speed video frames of a rattlesnake striking a mouse.
And you’ll notice in the upper frame the fangs are just starting to penetrate the mouse. And the lower frame the fangs are just leaving the mouse. It’s less than two-tenths of a second between the first frame and the second frame. So it’s an extremely rapid contact injection from two glands of venom through those hollow fangs, and then release.
Interestingly, it’s only at this stage in the evolutionary history of snakes. This stage where three different times front-fangs evolved, it’s only at that stage in the evolutionary history of snakes that we get all these fancy signals. Bright colors in coral snakes, hoods in cobras, rattles in rattlesnakes, noise-making scales on the side of saw-scaled vipers, okay.
It’s only once you get front-fangs that you get all these sophisticated ways of basically saying is there a problem? Because if there’s a problem you’re gonna be really sorry,
okay. You’re going to be really sorry. And if you survive it, probably the next time you hear that shhhhh or see those red, black, and yellow rings, or see that hood raise up you’re going to go no way, you know. So it’s, it’s, it’s, it’s a fascinating thing about the history of snakes that we only see all the signaling once we get front-fangs.
Just exactly who this aimed, is aimed at, we’re still not entirely sure. I mean we know things that eat snakes, we have observations of encounters between snakes and various birds and especially carnivores. We know there are some kind of carnivores like weasels and mongooses that are especially good at taking on snakes. But we’re still wondering sort of who does all this matter to, and I’ll come back to that in just a second.
[Slide text: “bitten by Sinomicrurus macclellandii ~30 cm long, barely pencil-thick, felt no pain; after 6 hrs, difficulty moving; after 8 hrs died from respiratory paralysis.” (Kramer, 1977, Rev. Suisse Zool.); Photo: Asian coral snake]
I just want to stress it it doesn’t have to be a big front-fanged snake, and I’m stressing this for myself as well because I used to think that really little coral snakes for example couldn’t kill people. Well this is a species of Asian coral snake, and one the size of a pencil, killed an expat German herpetologist working in Nepal in the early ’70s.
On 9/11 a American herpetologist named Joe Slowinski was killed by a krait in Burma about the same size, about the size of a pencil. I would not have predicted that the krait that killed Joe could have even scratched the skin of an adult human male, but he died from the, from the venom. So, so even the smallest front-fanged snakes are extremely significant in terms of their ability to deploy a punishing bite.
[Slide text: Snake Detection Theory, part 2: ≥50 mya front-fangs became a problem, mainly because we scare snakes!; Images: Phylogenetic tree of primates shown with the timeline for front-fangs in snakes, and photo of a gaboon viper camouflaged in leaves on the ground]
So that gets us to the second part of the snake detection theory, and that is something like about 50 to 55 million years ago front-fangs became a big problem. And the main reason is because snakes are afraid of us, okay. I’ll show you some evidence in just a minute, but most of the reason that primates get bitten by venomous snakes is not because venomous snakes want to eat us, but because they’re afraid of us.
Does everybody see the gaboon viper in the picture there? It’s an impressive problem to work in a place with forest leaf litter and a snake like that lurking. Waiting, not waiting to be stepped on, in fact hoping to not be stepped on, but if you step on it you’re the problem.
[Slide text: Front-fanged snakes do eat primates…; Photos: Gaboon adder (~1 m, ~2 kg) eating a blue monkey (~2 kg)]
So like I said front-fanged snakes do occasionally eat primates. Here’s one of the records we have. This is a gaboon viper swallowing a blue monkey in Equatorial Africa. It’s a quite large viper with a very big head, and a quite large prey item as well.
[Slide text: Probably much more often, they bite defensively & we pay attention! Black Mamba, Cape Cobras, Gaboon Vipers, Jararaca, White-tailed Lancehead, Puff Adder & unidentified venomous snakes have killed a Chimp, Orangutan, galago, Buffy Tufted-ear Marmoset, Chacma Baboons, Patas Monkeys, Blue Monkeys, & Rhesus Macaques “young Baboon was bitten by Cape Cobra while foraging under vegetation—died an hour later, screaming all the way.” T. Phelps, pers. Comm.; Photos: Baboon after being bitten by Cape Cobra]
But probably much more often venomous snakes, front-fanged venomous snakes, bite defensively, and as a result we have paid attention to them. So I’ve just listed here some species of venomous snakes we have records of killing various primates. And the killers include black mambas and so forth, and the primates that have been killed range from chimps and orangs down to patas monkeys and so forth.
This is not something we’re very likely to see if you think about it, so I’m kind of surprised that we even have this many records. But we, we know it happens.
[Slide text: 11 strepsirrhines, 1 tarsier, 5 Old World, & 7 New World anthropoids monitor &/or harass 1 harmless, 5 constrictor, & 7 venomous species; Photos: White-faced capuchin monitoring a 3 m boa constrictor, and yellow baboons (5-10 kg) around black mamba (~3m & 2kg)]
We have a lot more records of various primates, the strepsirrhines are the lemurs and lorises, everybody else is in the other group. We have lots of records of various kinds of primates mobbing venomous snakes. So the photograph on the lower left is a bunch of juvenile baboons in Amboseli National Park clustered around about a nine foot long black mamba, an extremely dangerous snake, and yet those little baboons are not running from it, they’re attending to it. And they’re, they’re basically chatting among themselves about what is this thing? And how should we regard it? And so forth.
On the right, and I know this is hard to see, but that’s the point. On the right just below the words three meter boa constrictor is a three meter boa constrictor, fully exposed in the leaf litter. That’s a snake about this big around. And up just to your right of the words white-faced capuchin there’s a cebus monkey looking down, staring intently, and I would say from my own field experience almost in, almost certainly chattering ferociously at this boa.
[Slide text: Our observations underestimate serpentine threats to primates; Photos: Various snakes, including emerald tree boa, and Amazonian tree boa (2.1 m, 650 g) with dead squirrel monkey (~600 g)]
So to sort of summarize up till now, I think the observations we do have tremendously underestimate the threat of snakes to primates. And it’s just one kind of dramatic example that there are a number of species of tree boas in the new world tropics, probably the most famous one is the th—on the upper right the emerald tree boa, the rest of them are less colorful.
We know quite a lot about their feeding biology relatively speaking, and what you’re looking at is the first record just published a couple years ago of a tree boa eating, killing and eating a primate. That’s a brown tree boa that weighed, it was about, let’s see, it was about 6, a little over 6 feet long, weighed about a pound and a half. And it consumed an adult squirrel monkey weighing almost as much as it did.
Okay, so when you add in what goes up on, what takes place on the ground, plus what’s going on up in the canopy with all these bright green, extremely difficult to see arboreal vipers, I just think being something like a marmoset would be about the most terrifying lifestyle I could imagine.
I mean, you would, you would have to be constantly concerned about the possibility that a clump of moss is actually a pit viper, not a clump of moss. That some bromeliad is not a bromeliad at all, it’s an ambush, perched green emerald tree boa, okay.
[Slide text: Moreover, ~20% snake species are front-fanged & >50% are mimics…but whom are they fooling? Birds & carnivores—visual, acoustic, cognitive!; Photos: Eastern hognose snake and cottonmouth]
So it turns out it’s even more complicated, because we think about 20% of snakes are mimics of venomous species, okay. So you know what mimicry is. This is always at least a three actor system. You have some species that’s the predator that wants to make a living eating, you have some species that’s genuinely dangerous, unpalatable, toxic or whatever that the predator shouldn’t mess with, and then you have a third species that’s kind of piggybacking on the first relationship and lying, okay.
The mimic is basically saying, “Don’t take your chance on me, I’m deadly, da da da.” Okay. And of course the predator wishes, so to speak, it could make a distinction and still profit from eating the mimics. This is a mimicry example from the southeastern U.S. On the left is an eastern hognose snake, on the right is a cottonmouth, a dangerous aquatic viper. And I’m quite familiar with both these species in the field, and I still would not just grab for that eastern hognose snake without giving it a closer look.
Right, okay. I hope you’re impressed by that. So again this raises the question well who are the actors? You know who, to whom does it make a difference? These displays. And who is being fooled by mimicry? Or not. I mean this is a real natural history puzzle, and I don’t think we really have the answer.
[Slide text: Anthropoids are visual, acoustic, cognitive, & super-social weapon-wielders! “Use of club by wild white-faced capuchin to attack a venomous snake” (Boinski, 1988, Amer. J. Primatol.); Photos: Capuchin monkey, and terciopelo; Image: Phylogenetic tree of primates]
But I think that we’ve got to pay more attention to primates. Because, okay, we got various birds, we got various mammals, that are super visual, super acoustically perceptive, they’re smart, but primates are all of that plus they’re super-social, and anthropoids are weapon-wielders. And weapon-wielding means that you can deploy a deadly blow to a snake without getting in range, okay.
So they’re actually field observations, if any of you have been to Costa Rica or anywhere in Central America you’ve probably heard of what used to be called fer-de-lance, it’s now called terciopelo, it’s a extremely dangerous six to seven foot long viper. There are field observations of white-faced capuchin monkeys killing an adult terciopelo with sticks. Just coming down out of the canopy and beating the seven-foot pit viper to death with sticks, okay.
[Slide text: Super-social snakebite survivors spread the word! ~95% male Ecuadorian Waorani bitten once, ~50% >once -Larrick et al., 1978, Trans. Royal Soc. Trop. Med. Hygiene
“Most [Paraguayan Ache] males have been bitten at least once…usually after stepping on snakes while searching for arboreal game…having survived a bite they are called paje [magic].” -Hill & Hurtado, 1996, Ache Life History
“Mortality to dogs [only] 1-30%, depending upon the amount injected, snake size & species, victim size, bite location, & time elapsed” -Armentano & Schaer, 2011, J. Veterinary Emergency & Critical Care]
So not only that, we’re super-social. That means that we can spread the word. That means that a single encounter actually can ripple through a social, a cultural group of organisms. And all primates are to some extent social and cultural. The most dramatic evidence for what this might mean is actually, actually comes from humans. You can basically ask a blood sample using a particular immunological test whether or not this person has ever been bitten by a venomous snake, okay.
So you can take a blood sample, do an ELISA test, and it’s a conservative question, answer. Because to get the answer you’ve been bitten twice you have to been bitten by two different species of venomous snakes, okay. So if we, if we give Tom the ELISA test for terciopelo venom and we get a yes, we don’t know whether Tom’s been bitten once or 20 times. To get the answer twice from Tom, he has to have also been bitten by a bushmaster, or an eyelash pit viper, or a coral snake.
Yeah, you see my point? So just imagine this, this, this test was run on a lot of blood samples from some Ecuadorian indigenous people, in the, in the rainforest, Amazonian part of Ecuador. And the answer was 95 percent of the adult male Waorani had survived at least one venomous snake bite. Just let that sink in. I think it’s extraordinary. 50% of men survived two or more bites. So here out in this tribe of people who make a living from the forest, make a living in the forest, 95% of the adult males have experienced the trauma of a venomous snake bite, okay. I don’t know how many died, okay.
Now it’s, it’s got to matter to these people, snakes, right? The same thing comes in less quantitative form from Kim Hill and Maria Magdalena Hurtado’s studies of these people in Paraguay called the Ache. Most Ache males have been bitten at least once, usually stepping on snakes while they were searching for arboreal game. So these, these indigenous peoples are out with their blowguns or their bows or their or their homemade shotguns, and they’re looking for game in the canopy, and they step on a fer-de-lance or step on a bushmaster and get bitten.
Now of course I’d like to know about other organisms, smaller organisms, especially non-human primates. And we have no information on that. The closest thing I can get to so far is a recent analysis of snakebite mortality in the United States to dogs. So I’m just using dog as proxy for a mammal, you know somewhere in this range. And again to my surprise, although I’ve had a dog be bitten by a venomous snake before. To my surprise, 70 to 99 percent of all dogs bitten by venomous snakes survive, often without any treatment whatsoever.
So again the message, which which I must say was quite a surprise to me as a herpetologist, is that venomous snakebites are probably not nearly as often as I imagined fatal under sort of non-western hospital medical care situations. And that means that venomous snakebites can be a really big part of the life of an individual organism, and in the life of a culture and of a social group.
[Images: Phylogenetic tree of Homininae, including Pan, Australopiths, and Homo, with Bipedality shown at ~5 mya and Big brains ~2 mya, and photos of the Lucy skeleton and Homo habilis skull]
So I’m gonna spend the last part of the talk talking a little bit about, more about our lineage. So we belong to a group of primates called the Homininae. And about seven million years ago, six to eight million years ago, our ancestral lineage split into two parts. And one of them oddly enough has no fossil record, and has left us with chimps and bonobos. They’re placed in the genus Pan. The other lineage has a relatively rich fossil record, and it’s left alive today, us.
Okay, so on the one hand you have chimps and bonobos, on the other hand you have these, all these various fossil taxa called Australopaths, Australopiths, excuse me. And among them is perhaps one of the most famous fossils of all time, Lucy. Everybody know about Lucy, well Lucy is especially spectacular and famous for, because, first of all she’s about three and a half million years old and she’s an australopithecine. But also because she’s so complete.
This was the first clear evidence that we got a bipedal pelvis before we got a big brain. So Lucy has an intact, largely intact skeleton. Certainly intact enough we can tell she walked upright, and there’s enough of her cranium there that we can tell she did not have a particularly large brain compared to modern humans.
So we know from the fossil record from comparisons among various fossils and stuff that about six to eight million years ago during a period of time when equatorial forests were shrinking in Africa, and savanna woodland habitats were expanding, more open habitats. There was this divergence in these ancestral members of our lineage, and today we have left chimps and bonobos, and us, okay.
And we’re from the savanna woodland lineage. This has led to what’s called the savanna woodland hypothesis of human origins, that with this drying, opening up of the forest into savanna we became bipedal, then we got big brains, okay.
So kind of keep that in mind, we got bipedal something like around three to four million years ago, maybe five million years ago. We got big brains starting about two million years ago, okay.
[Slide text: Testing the “savanna ape hypothesis”: Chimps, Bonobos, & Lucy’s lifestyle? -Chimps: male-dominated, aggressive -Bonobos: female coalitions, “the sexy ape” -Generally forest dwellers, unlike ancestral humans -What would a savanna Chimp be like?; Images: Drawing of chimp-like animals standing upright in a forest, and phylogenetic tree of gorilla, chimpanzee and bonobo, and human with drawing of the head of each]
Well you can imagine if you were an evolutionary biologist one thing you know is that convergent evolution is extremely widespread, okay. You can probably think of examples, you know, things that fly have wings, be they bats or birds or pterosaurs, okay, we could just go on and on with ichthyosaurs and dolphins and so forth. So we expect convergent evolution, that is the evolution of similar characteristics under similar situations.
So I like to think that at some point, in fact I’m sure this must have happened. Some anthropologists, some primatologists, some evolutionary biologists were sitting around a fire having a beer, or glass of vino tinto or whatever, and somebody said, “You know convergent evolution is so widespread, wouldn’t it be cool if there was a population of savanna chimpanzees? Because we could make some predictions about them. You know if the savanna ape hypothesis of human evolution is really true, we could make some predictions about what savanna chimps might be like. They ought to be more like Lucy, you know they ought to be more like us than forest chimps.”
Well as it happens, virtually everything until about 15 years ago known about chimpanzees was based on studies of forest chimps, and bonobos only live in forests. So they’re generally not like what we’d expect as this sort of savanna ape thing. As it also happens though
[Slide text: Jill Pruetz’s savanna-woodland Chimps! Http://www.nationalgeographic.com/explorers/bios/jill-pruetz/; Photos: Jill by her computer with an ape skull on her desk and holding a wooden spear, and three photos of woodland chimpanzees]
there’s a woman named Jill Pruetz who just left Iowa State to move back to her home state of Texas as a professor. And for the last 15 years Jill has been studying a population of savanna chimps in Senegal, okay. And it is just mind-blowing. So how many of you have ever heard of Jill’s studies of savanna chimps?
Yeah, and that. So let me tell you, first of all to my eye, they’re more sparsely haired than forest chimps. I don’t think anybody’s measured this yet, but I swear they’re less hairy than forest chimps. They take refuge from bad weather in caves. They’re not afraid of fire. They don’t make fire, I think that would be beyond credulity
right? And they make spears for hunting vertebrate prey. So it turns out, I mean we know that chimps eat a fair amount of vertebrates, okay, they’re probably, they’re famous films of the, of the forest chimps chase, the male forest chimps chasing these colobus monkeys, colobus monkeys through the forest, and grabbing them, and tearing them apart and eating them. It’s very, extremely loud, noisy, violent, chaotic and so forth.
It turns out in Senegal most of the hunting is done by the female chimps. And when they spot a hollow cavity in a dead tree that might house a galago, also knows a bushbaby, which is a small lemur relative. They go over and break a sapling off, of a chosen length, they sharpen one end with their teeth, and they use it as a thrusting spear, a lance. And they thrust it into the cavity of the tree. If they feel something soft they thrust again, they pull it out, they inspect for blood, smell it. And if they have evidence there’s a galago in there, they rip into the tree, and get the galago, eat it.
And unlike the forest chimps, the males, they often share meat with the other members of their group, okay. Isn’t that incredible? I find it just mind-blowing, and I’m so surprised that more, not only just not more lay people, but most of my evolutionary biologist friends don’t know about this yet. Jill’s work just hasn’t penetrated out into the mainstream. I have one of these spears in my office. So if you’re ever on the Cornell campus and you want to hold a spear made by a wild savanna champ, just drop by 251 Corson Hall, and I’ll let you under my scrutiny hold the spear which Jill gave me.
[Slide text: Jill’s Chimps are “herpers”!; Photos: Chimps walking in the savanna woodland, saw-scaled viper on the ground, and stick the chimps used to flip the viper off the path]
So it turns out Jill’s chimps are herpers. You’ve heard of birders, okay. Well herpers are like birders except they pick up amphibians and reptiles. And Jill and I are working on a paper right now. She has more than a hundred observations of chimp-snake interactions. And that’s something like five to ten times as much as there is in all the other literature on chimps. So forest chimps run into snakes from time to time, there are a few fascinating anecdotes. Savanna chimps run into chimps, into snakes all the time.
Jill has a video of a chimp seeing a python, picking up a large rock, and overhanding it like a softball at the python. She has a video of a chimp picking up a stick and beating it at a venomous snake. And in this case there was a saw-scaled viper on the path the chimps were walking on, and the chips stopped, looked around. Chose a stick that looks pretty much like the snake, snake stick I use to catch snakes with, and flip the saw-scaled viper off the path, okay.
[Slide text: Bearded Capuchins (Sapajus)—“New World Chimpanzees”?; Photos: Early human spear with horse bones, savanna chimp spears lined up, and bearded capuchins including one holding a stick near a snake hidden in a crevice with red arrows pointing at the snake and stick]
So I’m going to close with a, one last example, and again we’re going to keep convergent evolution in mind. I mentioned cebus monkeys earlier. These are the capuchin monkeys of new world, quite famous for for various reasons, including some of Frans de Waal’s fascinating research on the origin of morality and so forth. Well, let me set this up by showing, saying something about the left two pictures.
The inset left photograph is a field sample of savanna chimp spears from Jill’s fieldwork one season. So that’s a bunch of spears that savanna chimps have made that she’s going to measure and so forth.
The main photograph on the left is of one of the oldest known human spears. It’s from a place called Schöningen in Germany. It’s about three hundred thousand years old. It was found among some horse bones that had been butchered. It’s a fascinating piece of material culture. There are a number of these spears from Schöningen, enough that they could take one and section it.
It turns out it’s made, the spears are made from spruce and pine. If you look at it you’ll see it’s shaped functionally like a javelin. It has a thicker mid-part for accuracy, and a sharpened, fire sharpened, it turns out, tip. And I think, personally, most fascinatingly, when they cross section these Schöningen spears, three hundred thousand years ago they were using stone tools to make javelins.
And they were carving the javelins offset from the soft center of the trunk. So three hundred thousand years ago we were making spears that were harder and more effective than they would have been if we carved them out of the center of the trunk, okay.
So there we have spears made by chimps, and I argue that these are fashioned weapons by the chimps, admittedly very crudely fashioned weapons. We have much more sophisticated fashioned javelins. So the chimp things are called lances, that’s a spear used for thrusting. The, the three hundred thousand year ago Homo spears are, are javelins, they’re throwing spears.
On the right are some animals called bearded capuchins, which live in the savannas and Cerrados of Brazil. It turns out within this new world lineage of monkeys called the capuchins there was a divergence about seven million years ago, coincidentally. And one lineage is what we call a white-face capuchins that are mainly western South America and Central America.
And the other lineage, which have slightly bigger brains, more inclined to use percussive tool technology, that is to use hammers and anvils. These bearded capuchins recognize two kinds of snakes.
So there’s probably 20 or 30 kinds of snakes in their environment as a herpetologist would describe them. The bearded capuchins recognize two kinds. One kind consists of boa constrictors, vipers, and viper mimics. And the other kind consists of everything else.
And when they find one of those snakes that’s in the everything else category, which to me is about 20 species, they just grab it, take a bite or two out of it, and toss it. When they find the first category, a boa, a viper, or a viper mimic they pelt it with stones. They pelt it with debris. They even take sticks and thin one end and jab at the snakes when they’re hidden in crevices.
And actually interestingly you see that red arrow, the lower red arrow. It’s pointing to a snake in a crevice, and the people who did this work sent me their photographs to identify the snakes. And they had identified all these snakes as vipers, and by enlarging the pictures I could tell this is actually a mimic. So the mimicry actually fooled not only the monkey but also the biologists that were studying the monkeys, okay.
So here what I would claim is the independent evolution of weapons, or at least proto-weapons, three times. Once in chimps, once in our lineage, and as sort of what I call proto-lances in these bearded capuchins in the Cerrados, the savannas of eastern Brazil.
[Slide text: What’s next? -Fossils & molecules -Snakebite incidence? -Primates & snakes database -New questions…; Photos: Capuchins in a tree and large snake in water with its head sticking out]
So I think that Lynne Isbell’s part of this theory is very well supported. There’s more to do, but I think the evidence for snakes influencing primate evolution is quite strong at this point. I think the evidence for primates influencing snake evolution is much flimsier, and that’s the part I’m working on right now.
All of us are really interested in the additional, additional new fossils that might shed light on this problem. Uh the use of molecular systematics to more precisely date these divergences. Obviously if there was strong evidence that for example primates arose earlier than snakes, then snakes cannot have affected the early evolution of primates and so forth.
I would desperately like to know what is the risk of snakes to wild non-human primates. And so what I’m trying to engineer now is a collaboration among various primatologists who have blood samples, and a person at the School of Tropical Medicine Liverpool who has the ELISA tests and knows how to do it with the various venoms.
The idea would be to ask hundreds of samples of several different species of primates all over the world, have you been bitten by a venomous snake? Okay. And of course I expect just as always the case, new questions to arise.
[Slide text: “The serpent crams itself with life warm & vibrant, for an existence without joy & emotion. It reveals the depth to which evolution sinks when it strips animals to the irreducible minimum to perpetuate life in naked horror” (Alexander Skutch, ornithologist); Photo: Young girl crouched on the ground looking at a snake camouflaged in leaf litter]
So I’m going to close with two quotes. The first is from an ornithologist. I’ve made fun of this ornithologist in print in two different books. He’s a very, he was a very distinguished ornithologist named Alexander Skutch.
He had rather wacky ideas, I think. He, he thought that predation was literally evil incarnate. And he, one of his last, possibly his last written works was a philosophical argument for letting predators go extinct. Even things like tigers and so forth. Because they were, he believed them to be inherently evil.
So he especially didn’t like snakes, so, he the only, and he didn’t he didn’t like predators in general, so the only raptors he liked were laughing falcons, which eat venomous snakes.
So in one of his books he said, “The serpent crams itself of life warm and vibrant, for an existence without joy and emotion. It reveals the depth to which evolution sinks when it strips animals to the irreducible minimum to perpetuate life in naked horror.”
Okay, and I tell you I read that about 30 years ago and it’s offended me ever since.
I, I spent my entire career, the outreach educational part of my career, trying to convince people to like snakes, especially venomous snakes. And I’ve always found this quote really offensive, and sort of hypocritical coming from a natural historian. And I think one of the things that the last five years of my work has done to me is made me think a little harder about what I’m really up against trying to convince people to like snakes.
We, we don’t know how much of this is innate, how much is of its culture or, cultural. But in any case we have a very deep, very ancient, very fraught relationship with snakes. And any attempt to sort of come to grips with that, to coexist with dangerous animals in the future, it’s got to involve recognizing that, facing up to it, solving the real problems that snakes might present.
[Slide text: “ We will conserve what we love, love what we understand, & understand what we’re taught” (Baba Dioum, Senegalese conservationist); Photo: Young girl crouched on the ground looking at a snake camouflaged in leaf litter]
And so my other quote is from Baba Dioum, a Senegalese conservationist who said at an IUCN meeting in 1978 “we will conserve what we love, love what we understand, and understand what we’re taught” and that’s, that’s where I see the possibility of a somewhat harmonious relationship between primates and snakes for the the coming centuries. So thanks for coming, thanks for your attention, I’m happy to answer questions.
[Tom] So you’re not alone in loving snakes. And I think it’s probably a clear autosomal Mendelian trait that there are people who fear snakes irrationally and people who love snakes
[Tom] irrationally. I happen to be among the latter group who loves snakes.
[Tom] And Pia my wife is, too. Can you speak to that? I mean, there really are people who really like snakes.
[Tom] Who want snakes for pets.
[Tom] Who admire them in nature.
[Tom] And there are people who you’ve already mentioned who shiver at the name
[Tom] of a snake.
[Harry] So should I repeat the question? So basically Tom’s asking how can it be, and how is it that we can have people with such disparate responses to snakes? And I’d first say sort of go back to my earlier comment that, that as a species we’re like that as well. You know, we have, we have religions that deify snakes, and we have religions that, that, that what is it, what’s the opposite of deifies?
[Harry] Demonize snakes, right. So, and I think that part of that at least is that we’ve always for the last 75 million years had these very polarized possibilities with snakes. On one hand, if you can see a snake first it’s got to be about one of the most easiest animals in the world to dispatch.
Just a blow to the neck, in fact a blow anywhere along the front half the body and you’ve disabled a snake. And then you can eat it.
So on the one hand there’s at least that to be attracted to. And then on the other hand if you don’t see the snake, well if it’s a reticulated python the last thing you’re conscious of might be the incredible pain of this mouth hitting your face, and then you get about 60 seconds before you you die from cardiovascular problems, you know.
Or you might step on a gaboon viper and you’ve got two days of stumbling around incoherent in the forests with pain, you know, for this thing that’s destroyed your leg. So so you could really have that kind of thing.
The second thing I’ll say is that people have been trying to claim and show innate fear of snakes for well over a century. And it turns out the literature is pretty hard to interpret usually, because surprising enough usually they don’t know what the whole history of the individual they looked at was.
So you know, you go show a bunch of young monkeys pictures of snakes and ask the question whether they’re afraid, but you don’t actually know what, what those young monkeys already knew, so to speak. So that’s a problem.
Then the third thing, I’ll just offer an observation, and that is, we’ll see if you fit this pattern. My impression is that not always but often people who are afraid of spiders like snakes, and people that are afraid of snakes like spiders. So the late Tom Eisner for example who who was of course Mr. In—Mr. Bug, Mr. Spider and everything, would not come in my lab. So Tom was a very dear friend of mine, I could not ever get him to go in my lab. He wouldn’t look at pictures of snakes.
And I have had a couple of very public, embarrassing incidents when large spiders ended up on my shoulder or in my lap. So my hunch is that for some of us no legs is intolerable, and eight is just fine.
And for others, like no legs is really cool and eight is like no way. So that’s
[Harry] that’s where I’ll stop, that’s where I’ll stop on that problem. Okay.
[Harry] That’s a, that’s a great question. So how do these people survive snakebites? Well, the result of a snakebite are going to depend on a lot of factors involving both the snake and the the victim, the size of each one, so bigger and bigger snake more and more venom injected, all else being equal. Bigger and bigger person, more tissue to absorb venom, less effect all else being equal. Species of snake matters, whether or not snake already bit something recently might matter, where the snake bit you and whether both fangs went in would matter, your health would matter.
Just this past week there was a tragic death in Costa Rica of a person bitten by a big terciopelo twice. And the person I understand had, was diabetic and had some other cardiovascular issues, so it’s almost like he had everything stacked against him.
And then there’s the matter of okay you survived but what? Well, people that have survived snakebite sometimes have horrible disabilities. I’ve seen people with missing digits, even missing feet. People with permanently crippled extremities.
So so all that is part of the range of survivable outcomes. And it’s very complicated. That’s one reason snakebite treatment is kind of complicated because it’s not just a one-shot you know do this, do that, and it works, you know.
If if you get bitten by a front-fanged snake in one family, the cobras and their relatives, they typically inject neurotoxins. And usually there’s some different, there’s some exceptions to what I’m going to say, but in many cases if you got medical treatment and got the proper anti-venom, you really wouldn’t much know that you’d suffered a potentially life-threatening snakebite, because you’d never have gotten to the respiratory collapse stage.
If you got bitten by a black mamba you might be in that stage in five minutes. But for most members of the cobra family it would, it would take longer than that. You would have got anti-venom, you would have felt the pinpricks of some fangs, and that’d be about it.
If you get bitten by a viper, it’s almost instantaneous pain, it’s severe. People talk about red-hot poker held to skin, things like that. And then comes discoloration, swelling, and more and more serious sequelae so… if you were gonna get bitten and you knew you’d get medical care, get bitten by a cobra. And if you, if you, I guess,
I don’t know what to say about the other possibility.
Just don’t get bitten. It’s pretty easy, it, once you’re alert to the possibilities and do things, simple things like wearing foot gear, not going out at night without flashlights, and so forth. Avoiding snakebites actually a pretty easy prospect.
Yes, Ken. Jeff.
[Audience] You had mentioned whether the snake had bitten anybody recently. Is there data on the reload time for various species? And, and is it a matter of hours, or days, or weeks?
[Harry] They could, I think that most venomous snakes could get off several venom-delivering bites in sequence. So getting bitten twice would be worse than getting bitten once. But there is a finite amount, and it does take them time to rebuild. I think that the places where they actually milk snakes for venom for research they often allow a month between milkings.
So it’s expensive for the snakes to make. There have been some measurements of the cost, it’s not, it’s not cost-free for the snake to build it, so.
[Audience] What do they make it from?
[Harry] Yeah, that’s a great question. So it turns out, I can’t give you a detailed answer because I’m not a biochemist, but I’ll tell you a simple answer, which it turns out that the molecules in snake venom are related structurally and evolutionarily to digestive enzymes. And ultimately act actually to pancreatic enzymes. And so one of the really major toxins in, in, they’re called phospholipids A2s or something like that. They’re actually homologs, they’re, they’re, they’re versions of a pancreatic enzyme.
So there’s a lot of work now actually on the biochemistry of how these venoms evolve by things like gene duplications and so forth. It’s a, it’s a very hot area of research, and it’s, I had to take chemistry twice, so.
[Audience] I seem to remember years ago reading a book by Archie Carr
[Audience] in which he described being bitten by a fer-de-lance
[Harry] That’s right.
[Audience] I believe it was.
[Audience] And he thought, “Oh I may be done for here.”
[Harry] That’s right.
[Audience] And he had hardly any, as I remember it, he had very little reaction. And he speculated that the fer-de-lance quote could choose whether to inject venom or not.
[Audience] Does that sound familiar to you? I mean.
[Harry] I, I knew him and I’ve read that ar—that account. And he was bitten by a large fer-de-lance, and he was in a remote place, and he, he thought he was done for, and then there were no symptoms.
And so a fair number of venomous snake bites, more from some species than others, are what we call dry bites, where there’s little or no venom injected. And so one of the things that’s interesting about these dry bites is they’re extremely easy to cure.
So you know, you wonder about folk remedies, and I’m not dumping on folk remedies at all. I’m sure that there are folk remedies that have a basis in an empirical blahdy blahdy blah right, and there may even be some for snakebite.
But when I was a kid in east Texas my mom said that if I got bit she was gonna split a chicken in half and put it over the bite, you know things like that. So the thing was depending on what bit me, you know if it was a blue racer that bit me that chicken would have worked great.
You know it wasn’t even a venomous snake, right. So so that’s the problem. Now Archie he got bit by a potentially extremely dangerous snake, no venom was injected. He speculated that maybe the snake was holding back. And there is some evidence that, that defensive bites at least some of the time involve less venom than feeding bites.
But I just wouldn’t want to, you don’t want to play that that poker game because I also know that in some defensive bites, like when somebody’s actually stepped on a snake, and abruptly caused it pain, and and probably we can presume extreme fear, the bites seem to be extremely like [crunching sound] you know.
So I, just don’t get bit’s the way to go.
[Audience] So when you talk about 95% of the people being tested and uh having been bitten by a snake, could you assume [inaudible]?
[Harry] That would be a pretty parsimonious conclusion, wouldn’t it. He, he asked if 95% of a group of people showed evidence of a previous venomous snake bite, wouldn’t you think the other 5% we’re probably just lucky, right.
[Audience] They’re getting dry bites.
[Harry] They’re getting dry bites, yeah. Yeah that’s, could well be.
[Harry] So I think if you think about the rest of the ape, the living apes, they’re all forest species. And bonobo’s a forest species. So I think, and almost all the range of the chimpanzee is in forest. So I think the savanna woodland chimps are, are derived savanna inhabitants.
[Harry] Yeah, so if you imagine like a tree of descent from an ancestor out to its living today relatives. Derived would be deeply up within the tree as opposed to characteristic of the base. Does that do it? Okay.
[Audience] So I’m a textile person. Does anyone design snakebite-resistant clothing?
[Harry] Yes, in fact I wear it sometimes. So you can buy various grades of convenience and cost in the, in snake gaiters.
[Harry] So they’re the one that costs the most, and is the most comfortable to wear, and the easiest to pack in your luggage is called Turtle Skin, and it’s, I think it’s a version of Kevlar. And it’s about a hundred and thirty dollars for a pair, something like that. But there’s, it works. I mean I’ve seen video of big eastern diamondback rattlesnakes striking this stuff and not going through it. So to me it seems a,
you know, if you’re going to do fieldwork in places with huh? What?
[Audience] Reasonable investment.
[Harry] Reasonable investment if you’re going to be doing field work in like dense grass, places where, just impossible to see, you know.
[Audience] So back on the subject of venom delivery, I’ve been told that that a young rattlesnake will deliver much more venom than an older rattlesnake.
[Audience] Is there any truth to that?
[Harry] No, and there’s, so it’s interesting that that’s a very persistent, widespread bit of lore. What’s true is that for many rattlesnakes, especially the ones that have quite a size change in, during their lives. And go from eating lizards to eating mammals, there’s a change in toxicity. And it turns out that the, the venom on a sort of drop per drop, milligram per milligram et cetera basis of those little rattlesnakes is much more toxic than the big ones.
But the quantity injected, another version of it is that the little ones don’t know how to control themselves, but the quantity injected by a big one is many times over what you get from a little one.
And so this is one time when I am willing to make a sort of categorical statement. I’d much rather be bitten by a little rattlesnake than a big rattlesnake in terms of likelihood of death, of likelihood of losing a digit or something like that. I think go with a little one, but just don’t do it, you know.
[Audience] So often you see pictures or even walking you see one snake. Is it safe to assume there’s other snakes?
[Harry] I think it’d be smart to assume there’s other snakes, yeah.
Yeah, no I’m not making fun of you. During certain parts of the year, and they’re quite obsessive about it. So the rattlesnakes I spent many years studying the males basically quit hunting for food for about a month while they look for receptive females. And in most rattlesnakes the females aren’t, don’t give birth every year.
So for example the timber rattlesnakes that we used to have in Ithaca and that we still have in Elmira, those females take about ten years to reach maturity, and only give birth every three to five years. So in any one year even if you had a 50:50 sex ratio, the number of males looking for partners compared the number of partners is very, very unequal.
And so, rattlesnake social systems typically involve the males, in, going in these really long distance movements, usually traveling in straight lines until they hit the trail of a receptive female. And then they their bab—behavior complete, changes completely. They become extremely intense tongue flicking every little pebble and grass blade, and then they start following the female. When they find her they start courting her, and she’ll often, how much you want to know about snake sex? I mean.
She’ll often, she’ll often keep the male at bay for hours or even days. And she seems to be trying to set up a situation in which another male comes along, and when there’s two male rattlesnakes, two male copperheads, two male cottonmouths and so forth, they they have this combat behavior in which they, it’s almost like an arm wrestling match so they try to push each other down.
And typically that only happens between two pretty matched size. If it’s a really little and big one, the little one goes ehh, you know. But if they’re matched they’ll fight for minutes or even sometimes an hour so. Usually the bigger one wins. Whenever you find two rattlesnakes fighting if you look around you can almost always find a female, and that’s what’s going on. They’re fighting for access to her, and she’s probably set that up so that they will compete, and she will mate with the one who’s the superior fighter.
[Audience] What were they doing?
[Harry] They were doing their version of what the rattlesnakes were doing. So in rattlesnakes the male’s usually bigger than the female, this is probably because, driven by this fighting thing. In water snakes and garter snakes, which are pretty closely related, the males are always quite a lot smaller, the females are quite a lot bigger. Probably driven by the bigger you are, the more babies you can have.
And it’s pretty common, usually every spring here in April or May I get phone calls or people just tell me oh I was just a Buttermilk or wherever and I saw this pile of water snakes, and what that is is a bunch of males and usually one big female, sometimes there might be two big females, but more frequently it’s one big female garter snake, or one big female water snake, and then all these little males. It can be four, five, six, eight, ten even. And they’re all vying for that one lucky break. That one jackpot, that one winning ticket, you know.
When she chooses them. That’s what you’re seeing.
[Audience] So they’re all on her.
[Harry] Yeah, they’re all, and they’re, they’re, they’re all nosing around. And court, snake courtship involves a lot of the male running his chin up and down the female’s back, and there’s a lot going on at the other end, too.
Well. It’s more interesting that bird mating, my gosh.
[Laughter] Tell, somebody should tell Fitz I said that.
[Audience] Harry can you just talk anecdotally about your going to the primatology conferences. I mean, have the, have the people you’ve interviewed said oh we actually do have a lot of data, and that’s what you’re gonna be writing about?
[Harry] Yeah, so I mean on average they might have zero or one observation, but, but I’ve gotten a lot by, I’ve been going to these meetings for about five years now, and so I’ve talked to a lot of primatologists.
But actually the most, the most, I don’t know if it’s the most interesting, but the funniest thing that’s happened is, so I’ve been, you know I’m a, I’m a, I’m in a, I’ve been in academia almost 40 years, so I’ve been going to meetings for a long time. All the way back from when I was a first-year grad student to now.
And so I go the primatology meetings, and nobody knows me. And I noticed this fascinating thing. You’ll be on the elevator, and you’ve got this name tag, and the younger students and postdocs and stuff getting on the elevator with you. And they’re kind of, they’re trying to read your name tag. And they’re trying to figure out whether you’re Matt Cartmill, or Ron Sussman, or you know this or that and they go nope. And then they’re not interested anymore. And they, they don’t talk to you at all.
It’s all, it’s all this, it’s, it’s all, it’s it’s almost like a bunch of little baboons, you know.
It’s all all interesting social behavior involving status, and contacts, and future possibilities. And man if your tag is the name of a herpetologist at a primate meeting, you’re nobody.
[Audience] Would the Appalachian snake handling religion be useful for your observations?
[Harry] Well I…
[Audience] It’s kinda like those monkeys standing around looking at snakes.
[Harry] Yeah, I mean it’s. I know something about that, and I’ve never been to it, although I got my PhD in Tennessee. But I’ve read books about it and seen videos of it um. But to me that seems sort of like a super derivative kind of, I don’t mean this as a nasty pun, but it’s sort of like a dead end thing, I don’t, I don’t really know what to do with it in terms of a broader picture like this.
I mean, they do it because they believe a passage in the Bible impels them to do that. And they often get away with it. But not always. And they do get bitten, and they do die from time to time. Like it seems like every five years or so at least somebody dies. And sometimes they they’ve had deaths in descendant generations of snake handlers, even. You know the son died, and the father died 14 years ago, and stuff like that.
Yeah, I mean it’s interesting but I don’t know what to do with it. How’s our time?
[Miyoko] Let’s take one last question.
[Audience] I know that venom isn’t your speciality, but given that snake venoms contain neurotoxins, digestive enzymes, chemotoxins, that sort of thing. Do you ever notice that the type of thing injected or the complexity of the thing injected varies by prey type or prey diversity?
[Harry] Ahh, that’s a great question. So, um things that eat lizards and frogs tend to be things that are neurotoxic, and those younger vipers that I mentioned earlier, they’re, they’re toxins as juveniles tend to be more neurotoxic-like. The venoms of the adults, and especially species that eat big, bulky things, they seem to be really what we call cytotoxic. They, they’re just, some are myotoxic, they, they’re destroying tissue like crazy.
And I think that, that’s, that’s the difference. It has to do with being able to really big, bulky things.
[Miyoko] Thank you, Harry, for a fascinating talk. Thanks for all the great questions.
[Harry] Yeah, thanks for coming, y’all. Appreciate it.
[Applause]End of transcript
Harry Greene from Cornell University’s Department of Ecology and Evolution, explores the theory that snakes and primates have influenced each other’s evolution for millions of years. The snake-primate relationship started about 75 million years ago with constricting snakes. 50 millions years ago, the origins of venomous front-fangs created an additional challenge to primates (and birds as well). In turn, primates’ sophisticated visual, acoustical, and cognitive abilities influenced the evolution of serpentine defensive displays and mimicry. For example, the ability of early hominids to hunt with weapons may be responsible for the origins of serpents’ long-distance weaponry in Africa and Asia. The long-term, evolutionary relationship between snakes and primates challenges and inspires efforts in snake conservation.