The Great Mental Models Volume 2 summary

A zebra grazes in the grasslands of southern Africa. Nearby, a lion crouches in the long grass. It crawls forward, stealthily approaching what it hopes will be its next meal. Once it’s close enough, it breaks cover and begins sprinting. The zebra spots it. The race begins.

The stakes are high. A zebra that’s been brought down won’t get a second chance to escape. The rule here is simple: slow zebras get eaten. What this striped equine needs, then, is speed.

The British peppered moth’s wings and body are beige and gray and covered in small black spots – exactly the color and pattern of mottled, lichen-covered tree trunks. That’s handy. Perched on a trunk, the moth is pretty much invisible to predators.

Or rather, it was handy. During the Industrial Revolution, factories began belching out clouds of sooty smoke. Slowly but surely, trees were covered in a thick layer of black grime. Suddenly, the moth’s markings didn’t help it blend into its environment – they made it an easy target.

A busy port in Italy, 1340. Dockers are unloading a ship. The cargo is plentiful – a reflection of the wealth generated by the newly opened trading routes between Europe and Asia.

In the hold, a rat sniffs the air. It scratches itself, hops onto a rope, and scurries onto dry land. It carries its own cargo – hundreds of fleas infected with a deadly type of bacteria. Wherever humans are bitten, death follows. By the end of the century, an unprecedented epidemic will have claimed hundreds of millions of lives. 

Leonardo da Vinci’s thirst for knowledge was boundless. He wanted to know everything.

And there was a lot to learn – so much, in fact, that he jotted down reminders in his journal to keep track of it all. How do you square a triangle? He’d ask a master of arithmetic to show him. How do the people of Flanders walk on ice? His friend Benedetto should know. What about repairing locks, mills, and canals – a specialty of the inhabitants of Lombardy? He’d need to find a master of hydraulics to explain that. The list went on.

Norman Bethune wanted to help people. And, in the early twentieth century, there were plenty of opportunities for a gifted surgeon like Bethune to do just that.

Medical services in Bethune’s native Canada were still too expensive to be easily accessible for working-class folk, so he opened a free clinic and advocated for universal health care.

Rural France, 1788. We’re on a farm looking at a chicken coop. It’s easy to see who rules the roost. Some hens have first dibs on food and peck at the rest of the flock. Other hens defer to this avian elite while pecking their inferiors. At the bottom of the pile is the underclass. These hens never peck at others.

Zoom out a little, and you can see that French society looks a bit like this coop. It, too, has its pecking order.