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I’ve always said that the argument from mind-brain unity is one of the most potent arguments for atheism, yet also one of the most overlooked. Virtually without anyone noticing, science has dissolved the ancient belief that the seat of consciousness is an immaterial soul inhabiting the body. Even though the inner workings of the brain are still a terra incognita that we’re just beginning to explore, we’ve collected ample evidence that the mind is a thoroughly material phenomenon.

We know that our brains are complex networks of neurons that communicate through electrochemical signals. Those neurons are made of complex molecules, which are themselves made of atoms moving and interacting in accordance with physical laws. From top to bottom, there’s nothing happening in our heads that physics and chemistry can’t grasp.

The mind is what the brain does. It isn’t a discrete center of consciousness, like a military command post issuing orders to its subordinates. It’s more like a storm, or a symphony: a stable, persisting pattern of activity that arises from the self-organization of simpler elements. And, it turns out, it matters a great deal what those elements are. All the way down at the atomic level, if you replace one with another or change the proportions even very slightly, it has profound effects on your psychology and your very self.

Lithium is the third simplest element in the universe, but if taken as a drug, it eases depression and evens out the mood swings of bipolar disorder. Towns and counties that have higher levels of natural lithium in their groundwater have lower rates of suicide and violent crime.

Other elements have the opposite effect. People, especially children, who are poisoned by lead atoms from gasoline or paint become more aggressive, violent and impulsive. Even a tiny amount can have lifelong developmental consequences. It’s often been suggested that the dramatic dropoff in crime rates that began in the late 20th century is thanks to the phaseout of lead additives.

Another basic element that’s needed for the functioning of the brain is iodine. A lack of dietary iodine causes lethargy, depression and intellectual disability, which is why it’s added to salt. Iodized salt is one of the simplest and most effective interventions humanity has come up with, whereas people who only use “natural” sea salt sometimes suffer health problems.

And all of these are just basic elements. As you move up the scale of complexity, you find molecules that have even more profound and subtle effects on how we think and feel. The right arrangements of atoms can make us alert or sleepy, can tranquilize us or make us belligerent, can aid concentration or lower inhibitions, can erase memory or improve it, can create an addiction or abolish it, can make us see or hear things that aren’t there or can banish those phantoms. Every time a person is cured of depression, anxiety or paranoia by pharmaceuticals, it testifies to the truth of the materialist view of the mind.

This goes to show that our personalities, our basic selves, arise out of chemistry and physics. We’re not set apart from the universe, we’re not supernatural loci of consciousness inhabiting material bodies. We are our bodies, and changes in them are changes in us. We’re part of the Democritean dance just like everything else.

Some might see this as demeaning or reductive, but I take the opposite view. I think atoms must be amazing if they can give rise to creatures as complex, intelligent and adaptable as us. Besides, this view doesn’t rob us of anything that makes us special or makes our existence meaningful. It couldn’t. As Egan’s law says, it all adds up to normality. Our capacity for love, for generosity, for courage, for curiosity, for everything that makes us human – those are all real. They don’t go away just because we know more about what causes them.

DAYLIGHT ATHEISM—Adam Lee is an atheist author and speaker from New York City. His previously published books include "Daylight Atheism," "Meta: On God, the Big Questions, and the Just City," and most...

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