*Note: I use the word “suicide” a lot in this article, not to refer to the symptom of depression but to certain animal behaviors.
Animals aren’t like humans, because unlike humans, animals aren’t selfish. Animals work together for the good of their species, even to the point of sacrificing their very lives so that others may live. Take the humble lemming, which, as shown in this Disney animal documentary from the 1950s, will literally jump off cliffs to prevent others from suffering from overpopulation.
By the way? All of the above is bullshit. (Some of you were starting to get worried for a moment there, I know!)
Lemmings do not jump off of cliffs to prevent overpopulation. The footage above, as is now widely known, was faked- the lemmings were actually pushed off the cliffs by the filmmakers. Yes, it’s true.
It may seem logical to assume that animals work for the good of the species- after all, isn’t survival of the species what evolution is all about? Wouldn’t it make sense that animals would evolve mechanisms to make sure that their species is as successful as it possibly can be?
In fact, this ties in to a popular evolutionary theory called “group selection” that had traction (off and on) up until the 1980s, and has even had a resurgence recently. According to group selection theory, natural selection does not work with individuals, but rather on groups. That is to say, a gene that causes a disadvantage to an individual may persist in a population because it provides an advantage to the entire group. Hence our suicidal lemmings.
The problem with the theory group selection is that the basis itself is flawed. We know now that evolution works at the genetic level, and is dependent on whether or not individual animals get to pass on their genes. The word “individual” is key here.
To explain using an example: say that there was a gene that caused lemmings to commit suicide when they noticed that population levels were getting too high for the environment to sustain. Seems grim but logical, right? Well, in order for this gene to actually work, there would have to be some members of the population that didn’t have the suicidal allele. Because otherwise, all of the lemmings would jump off cliffs and that’d be it for the species.
Multiple alleles for the same gene, like the one that determines eye color for humans, can coexist in a species just fine, so that’s not a problem. Here’s the problem with this:
See those dots? Let’s pretend that the blue dots are animals with a suicidal allele and that the orange dots are the animals in the population without it. I’ve even given the suicidal allele an edge by having it be more common in the population, increasing the odds that it will be passed on.
Ok, let’s wait a few months and check back in on our population.
It really doesn’t matter how widespread the suicidal allele was in the population- it was a suicidal allele. When animals kill themselves, they don’t pass on their genes- so no blue dots lived long enough to give their offspring their suicidal tendencies. Even if they had, the orange dots will always have an infinite advantage over the blue: they have a much better chance of living longer and passing on their genes. A trait which reduces an individual’s chance of successfully rearing offspring would never evolve- because that’s the exact opposite of how evolution works.
This is where the phrase “selfish gene” comes from. It’s not as though genes are actually capable of being selfish- it’s just that the ones that exist are the ones that were the most successful at propagating themselves in the past. The ones that weren’t successful- even if they were super nice, friendly genes- no longer exist.
Longtime readers of this blog might be quick to point out that I’ve discussed how other supposedly nonreproductive behavioral strategies can be maintained in a population, such as asexual and homosexual behavior. The key difference between these and our theoretical “suicidal” behavior is that asexual and homosexual individuals can still gain indirect fitness benefits by helping their relatives. Committing suicide in order to reduce the population to an environment’s carrying capacity may indeed benefit an entire species, but how is the now-dead animal sure that his sacrifice is benefiting his relatives in particular? A lot of individuals have to die all at once for this strategy to work.
The idea that evolution benefits individual genomes, not entire species, is evident when you study species that have, as I like to call it, evolved themselves into a corner. These are usually hyperspecialized species that have adapted to a single, very unusual habitat or have a very tight symbiosis with another organism. The popular giant panda, for example, is in trouble because its very specific mountain bamboo habitat is disappearing. Likewise, if the special fungi that leafcutter ants farm were to go extinct, so would they (and vice versa) because each provide food for the other.
Compare the delicate nature of these species with the adaptability and damn-near-impossible-to-eliminate-ablity of a species like, say, a brown rat or cockroach. In terms of success and numbers, those species are certainly winning over the likes of the giant panda, and will still be winning whether or not we turn the coveted bamboo forests of China into parking lots.
If group selection were a viable theory, one might assume that it would guard species against overspecialization. But species overspecialize because evolution doesn’t look ahead: in the short term, specializing can make a species wildly successful. It’s just not a good strategy for the long haul.
I’ll bet that many of us don’t even realize how many of our assumptions about animals end up sounding a lot like group selection. For example: when a prairie dog squeaks at a hawk, it’s to signal the others to run. When birds of a feather flock together, it’s because they have more eyes and ears to watch out for predators for each other. Heck, when any prey species does anything to signal that a predator is near, it’s to signal all its friends and save their lives, right?
I’m sorry to have to say this, but by human standards, many animals are just terrible people.
I’m not saying animals can’t behave altruistically- i.e., for the sake of others to the detriment of themselves- they do, all the time. However, animals generally behave altruistically because, in the end, there is something in it for them. Or at least their genetic material.
Take those famous prairie dogs. Much has been made of their complex predator alarm system- different calls for different types of predators, and even the distance, looks, and behavior of said predators. Upon hearing these hyper-specific calls, the other prairie dogs in the colony know which escape strategy to use.
Super cool, right? And given that the prairie dogs who first give the alarm are likely putting themselves at risk by making themselves more noticeable by predators, it’s a pretty selfless act. With one major caveat. Those selfless rodents are far less likely to call out if none of their close relatives are in danger.
It comes down to protecting your own genetic material once again, whether or not it’s housed in your own body. And this is true of practically all species that use alarm calls- and more often than not, these alarm calls can be used for even more selfish reasons. Great tits and other birds will frequently give alarm calls not but because a predator is coming- but because they want to scare their larger companions away from the food. Some species of antelope even fake alarm calls to keep females nearby. If a female starts losing interest in a male topi’s advances, he snorts as though a lion is nearby to scare her into moving close to him again.
Some animal signals that we’re used to thinking of as alarm calls or warnings for others in the group are actually nothing of the sort. Those of us in the eastern U.S. are acutely familiar with the white-tailed deer, and of the bright white tail that gives them their name. Well, the tail raising behavior is not, as is commonly assumed, a means of warning others in the herd. It is instead a communication to the predator– a way of saying “I see you, so pick on the guy without his tail up.” The fact that other deer may run at the sight of this is a side effect. The signal’s not meant for them.
A more dramatic version of this is found in gazelles, who perform a behavior known as stotting (or pronking, or pronging). A stot is a vertical leap, which the deer perform when they spot a predator. Stotting actually can slow down gazelles when they’re fleeing, since it’s literally just leaping straight up, but that’s kind of the point: not only are the gazelles showing the predators that they’ve seen them, but they’re proving that they’re fit enough to risk idiotic vertical leaps while they’re running away.
And I do mean idiotic.
Why are we so sure that stotting is a signal meant for the predator and not the other gazelles? Well, for one thing, gazelles stot more when they see coursing predators- your wild dogs and your cheetahs- than they do when they see ambush predators- your lions and your leopards. It makes sense, because in a flat out chase, a signal of how much endurance you have might get the predator to go after a weaker-looking guy. But in an ambush, you’d better dispense with the hopping and get the hell out of the strike zone. Companions be damned.
And as a matter of fact, whether or not an animal stots is a pretty good predictor of whether or not it’s going to survive an encounter with a predator. If you’re too tired to stot, you are pretty much doomed. So you can actually think of it as a kind of favor to the predator, when it comes right down to it. It shows them which individuals they’re going to have a shot at catching, and which they aren’t.
If we’re going to be honest with ourselves, most prey animals would very much prefer that one of their friends gets eaten than the predator go hungry anyway. Because a hungry predator will attack again- while a well-fed predator grants them a reprieve.
So, let’s come back to a fundamental principle here: why do so many prey animals like to live together in large groups? Most ungulates, for sure, but also flocks of birds, schools of fish, swarms of midges… you get the idea.
To understand why this happens, first you have to understand the very real risks this generates for the animals in question. Ever tried to spot a lone sardine in the open ocean? Well, how about a school of thousands? One is a lot easier to find than the other. And predators find them more easily too- so if grouping up is an anti-predator defense, there has to be a damn good reason for it.
The “many eyes” theory is a popular one: it suggests that animals in large groups can trade off the job of looking for predators with others as the day goes on, so that at some point everybody has a chance to relax and feed. The problem with this theory is that a lot of animals are jerks and don’t pull their weight when they don’t have to. In bighorn sheep, ewes with calves spend a lot more time looking for danger than ewes without calves do. In fact, if there are a lot of lambs in a group, the lamb-less ewes spend even less time looking out for predators, because the predators are more likely to go after the lambs than them. Isn’t that sweet.
In general, the rule seems not to be so much “more individuals, more vigilance,” but rather “at-risk individuals spend a lot of time looking for predators and the others mooch off of their efforts.” So while big males and females without young benefit from having more eyes in a herd, in the end, mothers and calves might not.
Let’s look at a couple facts. As predator risk increases, herd size tends to grow larger, and the space between individuals gets smaller- and interestingly enough, individuals that look like each other tend to segregate from those that look different. There’s a moral lesson in that somewhere, but we ain’t about morality here on Koryos Writes.
The most crucial fact of this is the spacing between individuals. If you’ve never seen oceanic predators all teaming up on a “bait ball” of small fish, it’s pretty amazing.
By watching this video, you might feel that something’s off about the way those herring are moving. Namely, why do they all stay in one place, so close together, so that at the end a whale pops up and managed to scoop a huge proportion of them into its gullet? It doesn’t seem like the, er, smartest strategy.
Guess what: it’s not. Not for the group, anyway. These animals probably would be better off, on the whole, if they moved the heck away from each other and all swam in different direction. So why don’t they?
The answer, as you may suspect, is that while this behavior is bad for the whole group, it can have extremely positive effects for a number of lucky individuals. That is why the reigning theory behind this behavior is called selfish herd theory.
Selfish herd theory states this: that when a hungry predator sees one prey animal, that’s the one he’s going to attack. 100%. But when a predator sees two animals side by side, each animal’s chance of being attacked decreases (in a perfect world) to 50%. Three animals side by side? Hoo boy, the risk goes down to 33% each. I like those odds a lot better.
Of course, not all spots in a herd are created equal. The very safest places in a herd are right in the center, surrounded by other delicious-looking targets on the outside. This is why the center of a herd is quite a coveted spot to be, and why you will actually often find the most socially dominant members of a prey group not out in the lead, but in the center.
In the video below, you’ll see the results of a study where researchers attached GPS trackers to sheep (red) and a herding dog (blue). Observe the way the sheep immediately bunch up when the dog gets close.
Those on the outside of the herdrun far more risk of being picked off, and the danger only increases the farther they lag behind their conspecifics. So when somebody spots a predator, they don’t separate- they bunch up, all attempting get to the center. It doesn’t matter how bad this can get for the group as a whole, since the benefits for those lucky few are astronomical. So long as their behavior of sticking to the center means they get more genes out- which it does- they’re going to keep producing babies with a stick-to-the-center mentality. And that’s why they call it a selfish herd.
Now, I left a few things out of this very complex topic: while there are a very significant number of downsides for prey to live in large groups, there are some upsides: less time is devoted to finding food individually (though you’ll then have to compete for it) and it’s a lot easier to find a mate.
Similarly, other theories have decent support as a reason for why animals gang up. The predator confusion hypothesis suggests that predators get more confused as the number of targets they have to look at increases (at least in small-brained predators like sticklebacks). Also, some herds do use their numbers as a means to gang up on predators- cape buffalo are one famous example. However, this depends on how big you are compared to your predator.
The point is that selfish herd theory doesn’t explain EVERYTHING about why prey animals group together. But it’s a pretty big factor.
A factor called “please eat my friends instead of me.”
Read on: To become even more disillusioned about the purity of nature, try my article about animal masturbation. To learn more about animals that evolve in really stupid ways, try chase-away sexual selection or brood parasitism. And here’s where I talk a bit about how traits like homosexual and asexual behavior can be passed on genetically.
References and Further Reading
Beauchamp, G. (2007). Vigilance in a selfish herd. Animal behaviour, 73(3), 445-451.
Bro‐Jørgensen, J., & Pangle, W. M. (2010). Male topi antelopes alarm snort deceptively to retain females for mating. The American Naturalist, 176(1), E33-E39.
Burger, J., Safina, C., & Gochfeld, M. (2000). Factors affecting vigilance in springbok: importance of vegetative cover, location in herd, and herd size. Acta ethologica, 2(2), 97-104.
Caro, T. M., Lombardo, L., Goldizen, A. W., & Kelly, M. (1995). Tail-flagging and other antipredator signals in white-tailed deer: new data and synthesis. Behavioral Ecology, 6(4), 442-450.<
Childress, M. J., & Lung, M. A. (2003). Predation risk, gender and the group size effect: does elk vigilance depend upon the behaviour of conspecifics?. Animal behaviour, 66(2), 389-398.
FitzGibbon, C. D., & Fanshawe, J. H. (1988). Stotting in Thomson’s gazelles: an honest signal of condition. Behavioral Ecology and Sociobiology, 23(2), 69-74.
Hoogland, J. L. (1995). The black-tailed prairie dog: social life of a burrowing mammal. University of Chicago Press.
Hoogland, J. L. (1996). Why do Gunnison’s prairie dogs give anti-predator calls?. Animal Behaviour, 51(4), 871-880.
King, A. J., Wilson, A. M., Wilshin, S. D., Lowe, J., Haddadi, H., Hailes, S., & Morton, A. J. (2012). Selfish-herd behaviour of sheep under threat. Current Biology, 22(14), R561-R562.
Møller, A. P. (1988). False alarm calls as a means of resource usurpation in the great tit Parus major. Ethology, 79(1), 25-30.
Morrell, L. J., Ruxton, G. D., & James, R. (2011). Spatial positioning in the selfish herd. Behavioral Ecology, 22(1), 16-22.
Quinn, J. L., & Cresswell, W. (2006). Testing domains of danger in the selfish herd: sparrowhawks target widely spaced redshanks in flocks. Proceedings of the Royal Society B: Biological Sciences, 273(1600), 2521-2526.
Reluga, T. C., & Viscido, S. (2005). Simulated evolution of selfish herd behavior. Journal of theoretical biology, 234(2), 213-225.
Rieucau, G., & Martin, J. G. (2008). Many eyes or many ewes: vigilance tactics in female bighorn sheep Ovis canadensis vary according to reproductive status. Oikos, 117(4), 501-506.
Taylor, R. J., Balph, D. F., & Balph, M. H. (1990). The evolution of alarm calling: a cost-benefit analysis. Animal behaviour, 39(5), 860-868.
Wiley, R. H. (1994). Errors, exaggeration, and deception in animal communication. Behavioral mechanisms in evolutionary ecology, 157-189.