Thoughts compete for a space in your brain.

Cat photos, news stories, beliefs structures, funny GIFs, educational videos, not-so-educational videos, and your thinking inventory is limited.

A thought without a brain to think it dies.

Now, we can treat thoughts as though they're alive⏤specifically, alive like germs.

That might sound weird, but stick with me.

Take jokes.

Jokes are thought germs that live in your brain, and when you tell the joke to another brain, you help it to reproduce.

Just like when you have the flu and sneeze to help it reproduce.

This germ gets into its host by snot through the mouth, and this one by words through the ear, but it's reproduction either way.

Logging on to your social media, then, is exposing yourself to everyone's mental sneezes.

Each post a glob of snot with a thought germ trying to get into your brain,

if not for permanent residence, then at least long enough to get you to press the share button and sneeze it with everyone you know.

In this analogy, then, a funny cat photo with the perfect caption is a super-flu.

Now, just as germs exploit weak points in your immune system, so do thought germs exploit weak points in your brain, a.k.a., emotions.

Once inside, thought germs that press emotional buttons get their hosts to spread them more.

Measurably more⏤well, except sadness; sad thoughts don't get very far.

Awe is pretty good, which is why websites that construct thought germs like biological weapons arm them with them titles like,

"7 $whatevers that will blow your mind" or "The Shocking Secret behind $ThisThing".

But anger is the ultimate edge for a thought germ⏤anger bypasses your mental immune system and compels you to share it like nothing else.

Being aware of your brain's weak spots is necessary for good mental health, like knowing how to wash your hands.

Because, even without intentional construction, any thought germ on the internet can, on its own, grow more infections as it spreads.

To talk about why, lets forget anger for a moment and go back to that cat photo.

Every photo ever taken is a thought germ, and it most die a quick death, like the bazillion cat photos⏤or baby photos⏤posted on the internet that are never shared.

But a mildly funny cat photo can grow into so much more,

because, just as transatlantic flights were the best thing to happen to germ germs, so the internet is the best thing to happen to thought germs.

For once on board, that cat photo can leap into other brains, and those brains might share it, and⏤here's the key point⏤occasionally, change it.

A Photoshop here, a tweaked caption there.

Most changes are terrible, but some make the thought germ even funnier, getting more brains to share it.

Which results in more changes and a shot at super-stardom.

Thus, a lowly cat photo can achieve global brain domination⏤at least for a few hours.

The internet, with its unparalleled ability to share and randomly change thought germs, can't help but make them stronger.

With jokes, that's awesome, but with angry germs, not always so awesome, no.

Angry germs, the more they're shared, undergo the same process⏤changing and distorting to be more aggravating.

These have a better chance of spreading than their possibly more accurate, but probably also more boring rivals.

But like plagues, thought germs can burn through a population too quickly.

Just watch your favorite meme-generating machine for a week, and you'll see the life cycle fly by.

However, some thought germs have found a way around burnout.

Now, I must warn you, depending on which thought germs live in your head and which you fight for, the next section might sound horrifying.

So, please keep in mind: We're talking about what makes some thought germs successful, particularly angry ones, and not how good or how bad the thoughts themselves are.

Deep breath; calm.

Thought germs can burn out because, once everyone agrees, it's hard to keep talking, and thus, thinking about them.

But if there's an opposing thought germ⏤an argument⏤then, the thinking never has to stop.

The disagreement doesn't have to be angry, but, again, angry helps.

The more visible an argument gets, the more bystanders it draws in, which makes it more visible,

which is why every group from the most innocuous internet forum to The National Conversation can turn into a double-rage storm across the sky in no time.

Wait, these thought germs aren't competing; they're cooperating.

Working together, they reach more brains and hold their thoughts longer than they could alone.

Thought germs on opposite sides of an argument can be symbiotic.

One tool symbiotic anger germs in particular can employ is you're-with-us-or-against-us.

Whatever thought germ just leaped to the front of your brain, push it back⏤this video isn't about that.

We're just talking about this tool, which makes it very hard for neutral brains to resist, and its divisiveness also grows its symbiotic partner.

This explains why, in some arguments, gaining more allies also gains more enemies.

Because though the participants think they're involved in a fiery battle to the death, from the anger germs' perspective, one side is a field of flowers and the other a flock of butterflies.

Of course, planting more flowers will get you more butterflies, and getting more butterflies will pollinate more flowers.

If there is some argument that splits the population and lasts forever, and that even the most neutral people find difficult to avoid,

you just might be looking at a super successful pair of symbiotic anger germs that have reached ecological stability.

Now, one final depressing thought.

Uh... I mean, one more awe-inspiring point that will reveal the secrets of⏤ah, actually, no, it's just depressing.

When opposing groups get big, they don't really argue with each other; they mostly argue with themselves about how angry the other group makes them.

We can actually graph fights on the internet to see this in action: Each becomes its own quasi isolated internet, sharing thoughts about the other.

You see where this is going, right?

Each group breeds thought germs about the other, and as before, the most enraging, but not necessarily the most accurate, spread the fastest.

A group almost can't help but construct a totem of the other so enraging they'll talk about it all the time,

which, now that you know how thought germs grow, is exactly what makes the totem always perfectly maddening.

Now, all this isn't to say that there's no point in arguing⏤that's a different video⏤or that the internet isn't amazing or that there aren't things worth trying to change peoples' minds about.

Thought germs of all kinds come and go.

But it's useful to be aware of how thoughts can use our emotions to spread,

and how the more rapidly a thought is able to spread, the more chances it has to become even better at spreading through random changes that are made to it.

Sometimes that's great, sometimes it's terrible.

But if you want to maintain a healthy brain, it pays to be cautious of thoughts that have passed through a lot of other brains and that poke you where you're weakest.

It's your brain, be hygienic with it.