To look at the charred remains of a bombed city, the staggering loss of human life, and the astronomical wastage of resources, one might conclude that war is the ultimate manifestation of human madness. From a purely modern, utilitarian perspective, war is an apocalyptic failure of reason. Yet, history is bathed in it. Is war a biological and psychological anomaly? A mere glitch in the human software? Why is it so persistent, universal, and structured?
To answer this, we must abandon political rhetoric, historical grudges, and moral philosophy. Instead, we must look at evolutionary psychology or how our behavioral algorithms were selected and neuroscience or how the physical hardware of our brain processes threat and empathy. Additionally, one useful theory uses mathematical game theory (how logical agents interact under competition).
When we analyze the empirical data across these three domains, a deeply unsettling scientific truth emerges, war is not a breakdown of reason. Rather, under specific neurobiological and mathematical conditions, war is a highly calculated, biologically and strategically designed behavior of human beings already programmed by evolution. It is the flawless execution of an ancient survival algorithm operating in a modern environment where it no longer serves us.
Why are we aggressive? Power? Resources?
In evolutionary biology, a human being like other animals tries to maximize inclusive fitness—its ability to survive and propagate its genes, or those of its close relatives. To understand the evolutionary nature (not justification) of war, we must look at our closest living relatives and the ancestral environments that shaped our cognitive architecture.
The Imbalance of Power Hypothesis
For decades, anthropologists believed humans were uniquely warlike. This changed drastically with primatologist Jane Goodall’s observations of chimpanzees in Gombe Stream National Park in the 1970s. She documented the “Four-Year War,” where a northern community of chimpanzees systematically hunted down and killed every male of a splinter southern group (Goodall, 1986).
Biologist Richard Wrangham formalized these observations into the “Imbalance of Power Hypothesis.” The data showed that chimpanzees (and ancestral humans) did not engage in pitched battles where the odds were 50/50. That would be evolutionarily irrational due to the high risk of injury or death. Instead, they engaged in opportunistic lethal raiding. If a border patrol of five male chimpanzees encountered a lone male from a rival group, the numerical asymmetry reduced the cost of attacking to near zero. The evolutionary payoff, elimination of a competitor, expansion of territory, and increased access to food and mates, was massive (Wrangham, 1999).
From an evolutionary standpoint, when the cost of lethal aggression is low and the reproductive or resource benefits are high, violence appears to be a biologically rational computation.
Parochial Altruism: The Engine of War
How did individual evolutionary self-interest scale up to the level of group warfare? The answer lies in a psychological trait known as “parochial altruism”, the combination of intense in-group cooperation (altruism) and out-group hostility (parochialism). It is like you and your brother against your cousin, you-your brother- your cousin against your neighbor, you-your brother-your cousin-your neighbor against someone from a different neighborhood etc.
Mathematical modeling by economist and evolutionary biologist Samuel Bowles has demonstrated that human altruism and human warfare co-evolved. Bowles analyzed mortality data from prehistoric hunter-gatherer societies and found that up to 14% of adult mortality was caused by intergroup violence. Bowles’ mathematical simulations proved that altruistic behaviors (risking one’s life for the group) could not have evolved in humans without the presence of frequent, lethal intergroup conflict. Groups with high numbers of parochial altruists survived wars and passed on their genes, while groups lacking these traits were wiped out.
Therefore, the psychological readiness for war, the willingness to die for your “tribe”—is not an evolutionary accident. It is a highly selected adaptation that ensured the survival of human genetic lineages in a world of resource scarcity.
Why do brains think US vs THEM?
If evolutionary psychology explains why we have the capacity for war, neuroscience explains how the brain executes it. The human brain is a biological machine, and neuroimaging studies (fMRI) reveal precisely how this machine rationally reconfigures itself to permit the killing of conspecifics (members of the same species).
The Speed of Prejudice: Amygdala Activation
The brain’s threat-detection center is the amygdala, a deep-brain structure heavily involved in processing fear and aggression. Neuropsychological studies demonstrate that the human brain categorizes individuals into “in-group” or “out-group” with terrifying speed.
In seminal fMRI studies, when subjects were shown faces of people from different racial or cultural out-groups, the amygdala activated within 30 to 50 milliseconds—faster than conscious perception. The brain registers the “other” as a biological threat before the prefrontal cortex (the seat of conscious reasoning) even knows a face has been seen (Phelps et al., 2000). The brain rationally primes the body for a “fight or flight” response based entirely on tribal categorization.
The Dark Side of the “Cuddle Hormone”
Perhaps the most striking evidence of the neurobiological rationality of war involves oxytocin. Popularly dubbed the “love hormone,” oxytocin promotes bonding, trust, and empathy. However, neuroendocrinological data reveals a sinister duality.
A landmark study published in Science by Carsten De Dreu and colleagues tested the effects of oxytocin during intergroup games. They found that administering intra-nasal oxytocin did indeed increase trust and cooperation—but only toward in-group members. Simultaneously, oxytocin significantly increased defensive aggression and preemptive strikes against out-group members (De Dreu et al., 2010). The neurochemical that allows us to love our family and defend our nation is the exact same neurochemical that drives us to preemptively slaughter our neighbors. It is a precise, dual-action neurobiological lever designed to maximize group survival.
Dehumanization and the Medial Prefrontal Cortex
The greatest psychological barrier to war is human empathy. To kill a fellow human, the brain must bypass its natural empathetic constraints. Neuroscience shows us exactly how the brain achieves this through a process called dehumanization.
The medial prefrontal cortex (mPFC) is the brain region responsible for social cognition—it activates when we think about other human beings, allowing us to attribute minds, feelings, and humanity to them. However, researchers Lasana Harris and Susan Fiske discovered a chilling neural loophole. When subjects were shown images of extreme out-groups (such as enemy combatants or societal outcasts), the mPFC failed to activate. Instead, the brain processed these humans using regions typically reserved for inanimate objects or disgusting concepts, like the insula (Harris & Fiske, 2006).
By neurologically stripping the enemy of their human mind, the brain removes the cognitive dissonance associated with murder. What we call “dehumanizing propaganda” in wartime is actually a deliberate hack of the mPFC, making the act of killing neurologically permissible and, given the perceived threat, biologically rational.
Collective Neuroscience: The Hive Mind and Sacred Values
War is not just individual murder; it is coordinated, state-level violence. When we look at collective human behavior, we see that populations act like a macroscopic neural network, driven by neurological synchrony and the processing of so called “sacred values.”
Neural Synchrony and De-individuation
During the build-up to war, nations experience a psychological phenomenon known as de-individuation or loss of individual identity. Individuals lose their personal identity and merge with the collective state – as if they are one large organism. Recent advances in “hyperscanning” (scanning multiple brains interacting simultaneously) show that when groups engage in coordinated rhythmic rituals, such as military marching, chanting, or listening to aggressive nationalistic speeches, their brain waves literally synchronize.
This neural coupling bypasses the individual’s prefrontal executive control, making the collective highly susceptible to shared emotional contagion. The collective brain behaves rationally according to the survival of the group organism, even if it means the irrational suicide of the individual cell (the soldier).
The Neurobiology of “Sacred Values”
The most perplexing aspect of modern war is why political negotiations so frequently fail, even when peace is mathematically better for the economy of both nations. Neuroscience provides a definitive answer: the human brain processes “sacred values” entirely differently than it processes economic values.
Sacred values are core beliefs, such as the sovereignty of a homeland, religious holy sites, or national honor. Anthropologists Scott Atran and Jeremy Ginges, along with neuroscientist Gregory Berns, investigated how the brain processes these concepts. When subjects were asked to compromise on normal issues (e.g., trading goods), their ventromedial prefrontal cortex (vmPFC) activated, calculating a rational cost-benefit analysis.
However, when asked to compromise on a “sacred value” (e.g., selling out their homeland or their religion) for money, the cost-benefit regions of the brain shut down entirely. Instead, the temporoparietal junction (TPJ) and the amygdala activated—regions associated with rule-based moral processing and anger (Berns et al., 2012).
This data explains why offering economic incentives to stop a sacred conflict (like the Israeli-Palestinian conflict or ethnic territorial wars) often results in increased violence (Atran & Ginges, 2012). The brain perceives the offer to buy a sacred value as a profound neurological insult. Therefore, from a neurobiological perspective, continuing a devastating war over a patch of barren land is a perfectly rational output of the brain’s moral circuitry, even if it leads to economic ruin.
Mathematical Game Theory: The Cold Calculus of War
Beyond biology, we must examine war as a mathematical interaction between rational, calculating states. In international relations, states are modeled as actors seeking to maximize their security and power. Game theory demonstrates that even when two actors are perfectly rational and possess full cognitive faculties, the structure of the “game” can make war mathematically inevitable.
The Security Dilemma and the Prisoner’s Dilemma
The classic way to understand conflict is through a famous thought experiment called the Prisoner’s Dilemma. Here’s how it works with two countries.
Imagine two neighboring nations — let’s call them Country A and Country B. Both would genuinely prefer peace. War is expensive, destructive, and nobody really wins. So far, so sensible.
But here’s the catch. Each country is also thinking: “What if the other side is secretly building up weapons while we sit here unarmed?” Think of it this way. If both countries choose peace, everyone prospers — that’s the best collective outcome. But if one country arms up while the other stays peaceful, the armed country gains a massive advantage, and the unarmed one is left completely vulnerable. And if both arm up? They’re stuck in a costly arms race where everyone loses, just not as badly as being the only unarmed one.
So what does each country do? They each think: “If the other side disarms, I’m better off arming — I get the upper hand. And if the other side arms, I’m definitely better off arming too, at least I’m not a sitting duck.” No matter what the other country does, arming always looks like the smarter move. The tragedy? Both countries run through this exact same logic, and both end up armed to the teeth — locked in a standoff that’s worse for everyone than if they’d just trusted each other and chosen peace. This is what political scientists call the Security Dilemma: not a failure of reason, but almost an inevitable consequence of it. When each side acts purely out of self-preservation, the result is the very danger they were trying to avoid.
Fearon’s Rationalist Explanations for War
In a seminal 1995 paper, political scientist James Fearon asked a profound mathematical question: Since war is a costly lottery, and there is always an ex post (after the fact) negotiation that both sides would have preferred to the costs of fighting, why don’t rational leaders simply reach that agreement ex ante (before the fact)?
Fearon mathematically proved that war occurs between rational actors due to three specific game-theoretic breakdowns:
- Information Asymmetries with Incentives to Misrepresent: To get a better deal in negotiations, nations rationally bluff about their military strength and resolve. Because both sides know the other is mathematically incentivized to lie, neither side can trust the other’s data. War becomes the only mechanism to force the opponent to reveal their true capabilities.
- Commitment Problems (The Shifting Power Paradox): If Country A is growing stronger economically and militarily, Country A cannot mathematically commit to not using that power against Country B in the future. Because there is no global police force to enforce contracts, Country B makes a mathematically rational choice to launch a preemptive war now, while they still have a chance, rather than wait to be dominated later. The decision to strike first is a rational calculus of shifting probabilities.
- Issue Indivisibility: Some goods simply cannot be divided. You cannot have 50% of a king, or 50% of a sacred holy site. If the stakes are indivisible, rational bargaining fails, and a winner-takes-all war is the only logical resolution mechanism.
The Hawk-Dove Game and Evolutionary Stable Strategies
Borrowing from evolutionary biology, mathematical models of the Hawk-Dove game illustrate the rationality of aggression. Let V be the value of a contested resource, and C be the cost of injury in a fight.
- A “Hawk” always fights until it wins or is injured.
- A “Dove” postures but retreats if the opponent attacks.
If the value of the resource is greater than the cost of fighting (V > C), the only mathematically stable state, the Evolutionary Stable Strategy (ESS) developed by John Maynard Smith (1973)—is to be a Hawk. If a country calculates that the geopolitical resource (oil, strategic ports, regime survival) holds a value higher than the anticipated cost of casualties, initiating war is a mathematically sound, rational decision.
Conclusion: The Rational Tragedy
Why do we go to war? The answer is complex.
War is not a glitch; it is a feature of humans. It is the logical output of biological and mathematical systems operating exactly as they were designed by evolution.
- Evolutionarily, lethal aggression was a rational strategy for acquiring scarce resources and ensuring genetic survival, honed by the mechanics of parochial altruism.
- Neurologically, our brains are hardwired with circuitry that rationally categorizes out-groups as threats, selectively deploys empathy via neurochemicals like oxytocin, and deactivates the medial prefrontal cortex to allow us to kill without psychological collapse.
- Mathematically, game theory proves that in environments lacking a central enforcing authority, rational actors are frequently forced into conflict via security dilemmas, information asymmetries, and shifting power dynamics.
However, recognizing that war is biologically and mathematically rational is not a justification for it; it is a diagnosis. We are currently suffering from a severe “evolutionary mismatch.” The rational algorithms that served small bands of hunter-gatherers armed with spears are now controlling nation-states armed with thermonuclear weapons. The stakes of the game have changed, but our biological hardware has not.
Understanding the deep rationality of war is the only way to stop it. If we understand that the brain processes “sacred values” differently than economic ones, we can stop relying on flawed financial diplomacy. If we understand the mathematics of the Prisoner’s Dilemma, we can design international institutions with better enforcement mechanisms to alter the payoff matrix. We cannot rely on moral appeals to end war, because morality itself is often hijacked by the brain’s tribal algorithms. To achieve lasting peace, we must use science to hack our own neurobiology and outsmart the mathematical games we are trapped in.
