This Is Your Brain on Parasites summary

In the history of humankind, conflict abounds; from opposing tribes to warring countries to contradictory religions, people have always found a way to fight. But there’s another type of deadly conflict that has gone practically unnoticed for thousands of years – a hidden war of microscopic proportions.

It’s the battle between humans and parasites: viruses, worms, microbes and bacteria. In fact, this fight has been so formative that it has affected the evolution of both the human physique and human behavior.

For instance, the human body has formed complex defenses to ward off intruders. The skin prevents microbes from entering; the nose and ears are lined with tiny hairs that filter out parasites and our eyes produce tears to force out invaders.

But even when a microbe does make it into the body, it’s immediately met by other defenses. There’s stomach acid, which is so strong it could burn a hole through a shoe, and mucous, a slime that traps microbes in the nose to be expelled by the next sneeze.

That being said, parasites have a few things going for them. For starters, they greatly outnumber us. They can also reproduce at an incredible rate and are both intelligent and highly adaptable.

So while the majority of them might die, a few survivors can mutate, infiltrate our system and take full advantage of the habitat our body offers.

It’s this incredible capacity for survival that has led to parasite-related deaths in the past. Just take the bubonic plague, a bacterial infection that decimated a third of Europe in the Middle Ages. Or consider Columbus’s arrival in the Americas; his landing resulted in the eradication of 95 percent of the indigenous population by way of smallpox, measles and influenza. And there’s always the Spanish flu, which claimed more lives in 1918 than World War I.

It all goes to show that, while they may be invisible to us, parasites are a powerful foe. They’re also smarter than we might imagine, which is what we’ll explore next.