In moderation, religious and spiritual practices can be great for a person’s life and mental well-being. But religious fundamentalism — which refers to the belief in the absolute authority of a religious text or leaders — is almost never good for an individual. This is primarily because fundamentalism discourages any logical reasoning or scientific evidence that challenges its scripture, making it inherently maladaptive.

It is not accurate to call religious fundamentalism a disease, because that term refers to a pathology that physically attacks the biology of a system. But fundamentalist ideologies can be thought of as mental parasites. A parasite does not usually kill the host it inhabits, as it is critically dependent on it for survival. Instead, it feeds off it and changes its behavior in ways that benefit its own existence. By understanding how fundamentalist ideologies function and are represented in the brain using this analogy, we can begin to understand how to inoculate against them, and potentially, how to rehabilitate someone who has undergone ideological brainwashing — in other words, a reduction in one’s ability to think critically or independently.

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How religious ideologies spread

Similar to how organisms and their genes compete for survival in the environment and gene pool, ideas compete for survival inside brains, and in the pool of ideas that inhabit them. The famous evolutionary biologist Richard Dawkins has used this insightful analogy to explain how ideas spread and evolve over time. In his influential 1976 book, "The Selfish Gene," he refers to ideas as “memes” (the mental analog of a gene), which he has defined as self-replicating units that spread throughout culture. We are all familiar with many types of memes, including the various customs, myths, and trends that have become part of human society.

As Dawkins explains, ideas spread through the behavior that they produce in their hosts, which is what enables them to be transmitted from one brain to another. For example, an ideology — such as a religion — that causes its inhabitants to practice its rituals and communicate its beliefs will be transmitted to others. Successful ideas are those that are best able to spread themselves, while those that fail to self-replicate go extinct. In this way, some religious ideologies persist while others fade into oblivion.

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It is easy to see why religion quickly spread through culture once it emerged. When humans gained the cognitive capacity to reason and plan for the future, they became aware of their own mortality. The realization that oneself and all one’s loved ones will someday die is naturally terrifying, and this existential fear perfectly set the stage for anxiety-reducing ideas, like ones that offer a never-ending afterlife. But religions are complex ideas, and the psychological effects they have on minds go beyond just relieving anxiety.

Essentially, the brain is a biological computer, and an ideology is a set of coded instructions, or “cultural software,” that is running on the brain’s hardware. Esteemed philosopher and cognitive scientist Daniel Dennett insightfully described how ideas can control minds when he said, “The haven all memes depend on reaching is the human mind, but a human mind is itself an artifact created when memes restructure a human brain in order to make it a better habitat for memes.” In this regard, it is often not the brain that controls the mind, but the memes that compose the mind that control the brain. This is especially the case when the meme is a religion.

Religions mutate

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Like genes and gene complexes, when an ideology is replicated—or passed from one person or group to another — it undergoes mutations. As a consequence, different versions of that belief system are produced, which generate different types of behavior. As such, there are often good and bad variants of any given religion. For instance, there are moderate versions of Christianity and Islam, that promote qualities like a sense of community and a moral code that fosters ethical behavior. These ideas can be beneficial to the host organism, i.e., the religious-practicing individual. At the same time, there are harmful variants of Islam and Christianity — specifically the rigid fundamentalist versions — that cause the host mind to process information in a biased way, think irrationally, and become delusional.

Ideological viruses and mental parasites

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There are various types of viruses and parasites, and viruses are themselves parasites. While biological viruses are infectious agents that self-replicate inside living cells, computer viruses are destructive pieces of code that insert themselves into existing programs and change the actions of those programs. One particularly nasty type of computer virus that relies on humans for replication, known as a “Trojan horse,” disguises itself as something useful or interesting in order to persuade individuals to download and spread it. Similarly, a harmful ideology disguises itself as something beneficial in order to insert itself into the brain of an individual, so that it can instruct them to behave in ways that transmit the mental virus to others. The ability for parasites to modify the behavior of hosts in ways that increase their own “fitness” (i.e., their ability to survive and reproduce) while hurting the fitness of the host, is known as “parasitic manipulation.”

One particularly intriguing example of parasitic manipulation occurs when a hairworm infects a grasshopper and seizes its brain in order to survive and self-replicate. This parasite influences its behavior by inserting specific proteins into its brain. Essentially, infected grasshoppers become slaves for parasitic, self-copying machinery.

In much the same way, Christian fundamentalism is a parasitic ideology that inserts itself into brains, commanding individuals to act and think in a certain way — a rigid way that is intolerant to competing ideas. We know that religious fundamentalism is strongly correlated with what psychologists and neuroscientists call “magical thinking,” which refers to making connections between actions and events when no such connections exist in reality. Without magical thinking, the religion can’t survive, nor can it replicate itself. Another cognitive impairment we see in those with extreme religious views is a greater reliance on intuitive rather than reflective or analytic thought, which frequently leads to incorrect assumptions since intuition is often deceiving or overly simplistic.

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We also know that in the United States, Christian fundamentalism is linked to science denial. Since science is nothing more than a method of determining truth using empirical measurement and hypothesis testing, denial of science equates to the denial of objective truth and tangible evidence. In other words, the denial of reality. Not only does fundamentalism promote delusional thinking, it also discourages followers from exposing themselves to any different ideas, which acts to protect the delusions that are essential to the ideology.

If we want to inoculate society against the harms of fundamentalist ideologies, we must start thinking differently about how they function in the brain. An ideology with a tendency to harm its host in an effort to self-replicate gives it all the properties of a parasitic virus, and defending against such a belief system requires understanding it as one. When a fundamentalist ideology inhabits a host brain, the organism’s mind is no longer fully in control. The ideology is controlling its behavior and reasoning processes to propagate itself and sustain its survival. This analogy should inform how we approach efforts that attempt to reverse brainwashing and restore cognitive function in areas like analytic reasoning and problem-solving.

Bobby Azarian is a neuroscientist affiliated with George Mason University and a freelance journalist. His research has been published in journals such as Cognition & Emotion and Human Brain Mapping, and he has written for The New York Times, The Atlantic, Psychology Today, and Scientific American. Follow him @BobbyAzarian.