Marc Lewis Ph.D.

Addicted Brains


Is Addiction the Result of Brain Evolution?

Brains that evolved for goal-pursuit easily end up addicted.

Posted Nov 30, 2011

Brain evolution gone astray

What about addiction? We know that the tendency to pursue specific rewards (drugs, booze, porno, food, internet gambling, feet if you're a foot fetishist, etc.) grows easily into addiction. That's why so many of us are addicted to something. And we know that certain brain processes, like the rise in dopamine whenever you're reminded of the thing you want, are what make addiction happen. In fact, much of the prefrontal cortex seems prewired for addiction. Increased dopamine flow cultivates more and more synapses in the orbitofrontal (lower/prefrontal) cortex, and in the nearby ventral striatum—synapses that represent all the details, value, and importance of the thing you crave. Which dredges up more dopamine, so you wire up more synapses, and on and on it goes. No wonder we're easily addicted. Our brains seem perfectly designed for it. 

Addiction as a byproduct of brain evolution

Yet, brains did not evolve to make us better addicts! That wouldn't make sense. Addicts are not very functional (except when it comes to meeting certain needs), they often don't survive as well as most, and they make relatively lousy mates and parents. The brain processes that underlie addiction should have been weeded out, not strengthened, by natural selection.

Except that natural selection (evolution) doesn't explain everything about being human. A lot of human characteristics are byproducts, accidents, that arise from structures designed for different purposes. For example, half the people I know over the age of 35 have back problems. Did back problems evolve because they're adaptive? Of course not. Back problems are a result of walking around with an upright spine, something our ape ancestors didn't have to worry about. Having an upright spine is good for a lot of things. Like having your hands free to do stuff while your feet take care of locomotion. In the same way, I think that addiction is a byproduct (a nasty one, quite often) of having a brain designed to maximize goal-pursuit in an uncertain world.

A circuit evolved for goal-pursuit

The circuitry connecting the orbitofrontal cortex and ventral striatum is a beautifully crafted machine for learning what you like and pursuing it with single-minded purpose. Its fuel is dopamine. And this machine sends messages directly to the premotor and motor cortex. It guides behavior, action, in pursuit of the good things in life. This machine evolved so nicely because it's really really important to pursue valuable goals. And not all those goals can be imprinted in your genes. You need to learn them as you go along. So the goal-pursuit circuit is flexible. It learns. It's always open to try new rewards, and then to pursue them if they're as good as you'd hoped. That's why we pursue goals ranging from fruit, to fries, to Ferraris. We go after money—a relatively recent invention—because it's really nice to have. We go after romantic partners deemed to be attractive by movie and magazine images. We can learn to go after anything, full bore, if it attracts us. And that's how we get ahead in life. 

But it's also how we get addicted. The goal-pursuit circuit is a bit too flexible. Cocaine high. Oh yeah. That feels good. Want more. Got to get it. That drink at the end of the day. Feels good. Want it. Stop at the liquor store on the way home. These tendencies eventually cause us a lot of suffering, but they are simply byproducts of a brain that evolved to seek rewards, based on their attractiveness, and to pursue them with almost relentless energy.

When your back-ache gets bad enough, you start doing physio or yoga, so that you can use your upright spine to its best advantage. When your addiction gets bad enough, you'd best figure out how to use the goal-pursuit circuit for what it's designed for: to be successful and happy, to avoid suffering, and—of course—to feed the little ones back at the cave.

This and related topics are covered in more detail in my book, Memoirs of an Addicted Brain, to be released in the U.S. in March. Please also visit my website and (other) blog.