Knowing your neighbor is a big advantage for most animals, but it also limits how big societies can get.

Ever taken a job as a babysitter? Then you’ve got something in common with meerkats. Meerkats care for infants outside their immediate families, too – and they even go the extra mile while doing it, tidying each other’s burrows and offering delicious insect snacks to the babies in their care.

Just like humans, meerkats live together in societies, where they benefit from mutual cooperation. Many other vertebrates do, too – societies such as those of wolves, or birds like the Florida scrub jay, are based entirely around cooperative child-rearing. Cubs in a wolf pack even help their parents and other adults raise newborns. 

Cooperation can also bring powerful benefits when it comes to protection and security. Living in a society means more eyes and ears for spotting rivals and threats, and more paws and claws for fighting back against them. Elephants, for example, work together to safeguard their young by forming a shield to protect them against lions, while horses encircle their foals and kick outward when wolves approach.

So society offers benefits to its members – but these benefits are offered only to that exclusive, bounded group, and it’s obvious to group members when an outsider is in their midst. Vervet monkeys in Africa, for example, can tell not only when individuals are foreign to their group – they can even tell to which tribe the foreigner belongs!

Most animal societies are built around this individual recognition – recognizing and knowing each individual in a tribe in the same way that humans recognize everyone in their office or class. This feature limits the size of most societies; that’s why we don’t see thousand-strong prides of lions roaming the plains, felling herds of wildebeest. Nor will we ever see apes rising up, Planet of the Apes-style; the animals’ brains are too small to recognize all the individuals in such a large group. That’s why ape societies max out at around 200 members.

Humans manage to live in far, far larger societies, because we’ve broken free of the need to recognize each individual member of our own group. To understand how we’ve done this, let’s take a look at a species that resembles us more than we may care to imagine: ants.