Learning from suicidal salmon

The fish's journey home is extreme and deadly -- and it offers surprising insight into human extremist belief

Rafe Sagarin
April 1, 2012 1:00AM (UTC)
This article is adapted from the forthcoming book "Learning from the Octopus: How Secrets from Nature Can Help Us Fight Terrorist Attacks, Natural Disasters, and Disease," available April 2 from Basic Books.

Salmon go to great lengths to kill themselves. After a short few years frolicking in the open ocean, they may travel thousands of kilometers to get back to the precise stretch of the same river in which they were born. On this journey they will have to slip past the birds, bears, sea lions, and humans that gather at river mouths to feast on them. They must swim exhaustively upstream for many miles, using most of their energy reserves to leap up waterfalls or swim ladders (artificial waterfalls constructed on the sides of artificial dams) until they reach their spawning grounds, where their last gasps are spent producing eggs or fertilizing them with sperm before collapsing in death, never to see the ocean again.

From an evolutionary standpoint, it’s not hard to find sense in these suicide missions — the salmon are passing on and multiplying their genes in a habitat that has already been proven (by the adult salmon’s own experience) to produce strong and reproductively fit salmon. People tend to admire the determination of the salmon. At the very least, we generally don’t call the salmon “irrational” or “crazy” for their journey. We do, however, freely launch those pseudo-psychological assessments on human suicide bombers. Yet salmon and suicide bombers are not as different as their outward appearance would indicate. The most important difference between them is neither fins versus arms, nor gills versus lungs, but that the salmon (despite the dams choking up the rivers) still lives in the environment its ancestors evolved in for thousands of generations, while the suicide bomber does not. Suicide bombing is just an extreme case at the far end of a spectrum of behaviors related to establishing and reinforcing self-identity that impart survival to organisms.


The naturalist’s view on security doesn’t allow us to simply label something “irrational” and then dismiss it. Just as a biologist wants to get to the root of what makes a peacock grow such outlandish feathers or an immune system suddenly turn on its own host’s body, a natural-security approach tries to get inside these behaviors that compromise our security, tracing their roots back as deep in evolutionary time as possible and figuring out what they mean in today’s society.

Evolutionary psychologists, who study the ancient roots of modern human behavior, argue that religious fervor didn’t develop in the modern world but in a world completely unlike the one we have briefly inhabited now. In this early world, humans lived in small close groups that struggled constantly to obtain enough resources to survive. Only rarely did they encounter small groups of other humans, and if their interaction wasn’t about trading resources, it was likely because one group was trying to take the other group’s resources by force.

Yet almost all political analysis of human behavior tries to explain it within the narrow confines of the immediate sociopolitical environment. Some public commentators try to get us to broaden our thinking. Journalists try to remind the most short-sighted among us that there were clear signs of terrorist activity against Western targets years before 9/11. Historians admonish us to open our eyes and look at the thousands of years of history in places like Iraq and Afghanistan. Political scientists urge us to look at individual security crises within their global context. I fully support these viewpoints, but I suggest that analyses digging back ten, a hundred, or even a thousand years must be nested within a perspective that goes back orders of magnitude deeper into human, and biological, evolution.

Oddly, a virologist, Dr. Luis Villarreal of the University of California–Irvine, has made some key discoveries about human belief systems. The evolution and development of viruses, it turns out, is inextricably tied to almost every major evolutionary advance, including the rise of modern humans, in Earth’s history.

What Villarreal emerged with is a synthesis that traces the origins of human belief systems back to the earliest life forms, such as bacteria. The exact forms of these belief systems obviously differ between, say, a bacterium, a salmon, a chimpanzee, and a suicide bomber, but the mechanism is the same. In Villarreal’s theory, belief, as we know it in humans, is a form of addiction. And addiction in its pure form, according to Villarreal, is one of the oldest processes of self-preservation on the Earth, traceable to the earliest invasions of bacteria’s genetic material by viruses.

Although viruses seem to cause chaos in our daily lives—at the least, they cause sick days and frantic parents rearranging day care schedules, at worst they lead to epidemics that kill millions — the virus itself wants stability more than anything. In this sense, a virus is like a businessman trying to maintain a steady clientele. More particularly, the virus is like a drug dealer trying to develop a clientele of hardcore addicts. It does this by offering protection to its clients, something like a safe place to shoot up, shielded from the police or other junkies. This safe place is created by paired genes—called an addiction module by Villarreal — that the virus inserts in the bacterial genome.


One part of this pair (called the toxic gene) is destructive, killing all entering foreign bodies at will. If this gene was left to its own devices, it would destroy everything, including the host bacterium’s genome itself. So it is paired with a counterpart (the antitoxic gene) that confers immunity to the host. This simple opposing pair—aggressor and protector — provides a way to distinguish, even in the most basic organisms, self from nonself. If something is “self,” coming from the host’s own body or genome, the antitoxic gene allows it to reproduce. If something is nonself, a foreign invader, the toxic side destroys it. It’s easy to see why the bacterium, or indeed any other organism, would get addicted to this product pushed on it by the viral parasite — without it, any number of invaders, including the virus itself, could destroy the bacterium.

The story would end there with bacterial addicts if it wasn’t such a good system these viral pushers set up. When biological systems emerge with an idea that works, it gets made again and again. Sometimes the idea is replicated exactly; thus we humans have major components of our genome (especially those vital to survival) that are nearly identical to goats and fiddler crabs and even those earliest viral parasites. But often times, good ideas are merely mimicked, taking on different forms for different organisms in different environments, even as they maintain the same basic function.

A way to detect self from nonself is one such really good idea in biology. Nearly all organisms benefit from such a system. It allows them to identify who is likely to share their interest in producing common offspring and who is likely to disrupt that chain of genetic descent. It allows them to distinguish who to school with and who to swim from, who to eat and who to eat with. Even below the level of organisms, self–nonself identification is essential. In species where females mate with multiple males, the seminal fluid around the males’ sperm has evolved to protect its own sperm and destroy the sperm of a rival male.

As organisms get more complex in their behaviors, they need ways to identify potential mates and potential enemies. They need ways to assess a competitor’s intentions. They need ways to make friends and influence others. Villarreal argues that the same basic addiction system — a system that confers simultaneously both protective and destructive powers — fulfills all these complex needs of biological organisms.


Take the suicidal salmon. Young salmon cue into the precise chemical cues in their home stream. Then they make their way out to sea, traveling thousands of miles over two years or more, before returning to the precise part of the same stream in which they were born, in order to mate. While they may navigate by ocean currents and stars and magnetism in their open water phase, what gets them back to that precise stream riffle where they were born is the smell. Salmon possess a remarkably effective chemical-sensing organ called a vomeronasal organ (VNO). Villarreal argues that the VNO system is the same type of addiction module as the toxic/antitoxic gene pairs in viral-bacterial interactions. Indeed, a VNO system is another one of those evolutionary success stories that gets replicated in animals as different as salmon, snakes, and shrews.

For salmon, a sense of self and a sense of place are inexorably linked. Any particular salmon is literally defined by its home stretch of stream. In the salmon’s VNO system, home-like smells are intensified in the system and honed in upon, and non-home-like smells are rejected and effectively ignored. As a result, the salmon will relentlessly target their home spot, past anglers’ hooks and gaping sea lion jaws and enormous concrete dams with their artificial fish ladders as a small (and only partially effective) concession to the salmons’ unyielding will. What we admire as the incredible determination of the salmon is exactly the nature of self-identity addiction. The high threshold of acceptance into the “self ” category ensures that only the most fit will survive and reproduce. This addictive system, by the time it appeared in its particular form in salmon, already survived billions of years of relentless natural selection. What are some scattered predators or concrete barriers in relation to that track record?

Like the salmon VNO, our own behaviors have driven us to do remarkable things. Our behaviors allowed us to cooperate in complex ways and form strong groups, bonded for life. In small, clever groups whose members had a deep intimacy and mutual understanding and specialized in different tasks, we pulled through any number of forces—predation, bad weather, changing climates— that could have easily wiped out our weak and nearly naked bodies.


For salmon, group survival comes in part from a common set of olfactory cues that urge the fish to simultaneously migrate to natal rivers and spawn. But humans don’t have such a great sense of smell. The popularly bandied idea that invisible pheromones control our behavior, not to mention the endless iterations of supposed pheromone products purported to “drive women wild with desire,” appears to have little backing in olfactory science. While smell plays a subtle and not completely understood role in human mating, smells don’t play the dominant outward role in human identity. That is because higher primates and humans essentially turned our VNO systems off. The genes that form the VNO system are still there, but they don’t get activated. Those genetic changes have obvious outward manifestations. Have you noticed, perhaps while walking your dog, that we humans don’t scent mark or eagerly sniff one another’s nether regions when we run into a friend on the sidewalk?

But we do mark territory; just look at the graffiti scrawled across the walls in the tough neighborhood where Luis Villarreal grew up. That written marks were substituted for scent marks is a clue to the force behind our current sense of identity. Written symbolic language, which recent reexamination of the earliest cave paintings suggests may date back, not three or four thousand years, but perhaps as long as 30,000 years, is a uniquely human attribute and one that codifies our identities—especially our group identities.

Written language has a key role in codifying religious beliefs. As Villarreal points out, the word literate originally meant “one who can read holy scripts.” Not only are religious beliefs often spelled out in written tomes, but religious myths also contain curious references to written materials. God doesn’t just tell Moses the Ten Commandments; he gives them to Moses in written form on stone tablets. And when Moses grows angry with the Israelites for their idolatry, he smashes the tablets as a symbol of the broken bond between the Israelites and their one true God. The deference to written scripture goes beyond Judeo-Christian religions as well. A well-respected Japanese Shinto group, Oomoto, was codified in the late nineteenth century when Deguchi Nao, a supposedly illiterate housewife, suddenly had a vision that she transmitted into calligraphy that she scrawled across the walls of her cottage. This is not to say that nonliterate cultures can’t develop religious beliefs, but rather that written language provides a powerful symbolic shorthand for ideas that defy observable natural phenomena.


Defiance in the face of observable evidence is something that continually baffles outsiders trying to understand behaviors of individuals in tightly bound human groups—be they scientists trying to debate creationists or CIA agents trying to understand why someone would blow himself up for a cause. The rationalist-evolutionist deftly dismantles the structure of creationist theory with a few pieces of devastatingly incontrovertible evidence, but then can’t understand why the school board (freshly stocked with evangelical Christians) votes to “teach the controversy” in her daughter’s public school. People coming from this rationalist perspective tend to think that the resistance to rational testing of ideas is a weakness of religion — when in fact the opposite is true. Religious beliefs, perhaps more than other human belief systems, function well as a strongly addictive system because they substitute symbolic group identification for any type of rational-based test of group fidelity. The core ideas of religious conviction are universally true to believers and will remain so as long as adherence to religious laws is maintained, regardless of what some egghead scientist or analyst says.

Indeed, the high bar of irrational thought associated with most religions is a selective force that increases the strength of the belief system through time. Stream reaches that require salmon to make large leaps of gravity to get home and religions that require large leaps of faith for acceptance into the sect both enrich their populations with individuals that are especially capable of making these leaps. In part, this is an example of “honest” or “costly” signaling -- there is no bluffing your commitment to the group if you will injure or kill yourself on its behalf.

Just because they are deep-rooted does not mean belief systems are necessarily locked in forever. Certainly, we’re able to trade more primal evolutionary signals for modern ones. That is why a short, nearsighted, balding weakling, who would have been an evolutionary dead end in our hunter-gathering days, may still find a fine mate, especially so if he drives a Ferrari. If a modern human female can calculate that the resource-gathering ability of the Ferrari driver may make up for his obvious physical weaknesses, so too can a modern Israeli or Palestinian realize that coming to the negotiating table with an eye to the future rather than to the insults of the past will lead to a much better future than engaging in escalating acts of violence. A modern jihadist can recognize that continuing his education, learning new skills, and getting a
mainstream job will give him a far better chance of propagating his genetic code than committing an act of martyrdom. Still, many do not, and it would help to understand why they do not.

Adapted with permission from "Learning From the Octopus: How Secrets from Nature Can Help Us Fight Terrorist Attacks, Natural Disasters, and Disease" by Rafe Sagarin (Basic Books, 2012).


Rafe Sagarin

Rafe Sagarin is a marine ecologist and environmental policy analyst at the University of Arizona. His research has appeared in Science, Nature, Foreign Policy, among other publications. He lives in Tucson, Ariz.

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