Our brains have limited storage capacity. We can’t remember everything. We need a mechanism for deciding what to remember: emotion. In Palaeolithic times, a tiger sneaks into your camp at night. You’re awaken by screams. Your brain floods with chemical called Norepinephrine (adrenaline). It increases arousal and alertness, promotes vigilance, enhances formation and retrieval of memory, and focuses attention: ‘fight or flight’.
This scenario played out millions of times over 100,000 years. Unsuccessful responses got their hosts eaten. Those that survived prioritized space in memory due to heightened emotion. However you’re feeling creative. You think: ‘if I chop down a tree, cut it into poles, and stick them in the ground around camp – the tigers couldn’t get in!’
After the danger subsides your brain released Endorphins for pain relief, so positively buzzed, you don’t immediately dismiss the idea. You start chopping wood, and your brain keeps you motivated by rewarding you with Dopamine. As you look upon your work, you get a hit of Serotonin, which makes you feel satisfied, and reminds you to eat, sleep, and have fun.
As you settle down for the night, with your family safe, Oxytocin – the ‘love drug’ – is released. You resolve to show other members of your tribe how to build fences in the morning. Other tribes observe your fence-building activities, and build fences of their own. In this fashion the meme for fence building is passed on.