Online Community Building: Why Communities Decay

The first day of September 1993 was the beginning of an eternal September, a calendar month whose days stretched to infinity. Prior to this infamous day, there would be an influx of noobs onto Usenet each September. These were the arriving college freshman. They were not legion. They were few enough that they could be corralled and assimilated by Usenet veterans.

September 1993, however, was different. It was the day the gates of hell were thrown open and never-ending torrent of demonspawn descended on Usenet — like locusts, they devoured the community.

These locusts were AOL users. In September of 1993, the company granted Usenet access to their entire user base, which triggered an unending deluge of noobs into the Usenet community. Thus began the September that never ended.

Community Decay Over Time


There’s a website dedicated to documenting terrible YouTube comments. Its tag line is, “The aim of this website is to document and preserve the most retarded YouTube comments, so that people a hundred years from now can look back and take solace in the fact that the authors of these stupid comments have all since died.” The dude running the website even posts an analysis of why each comment is awful. He’s doing God’s work.

YouTube’s awfulness is so infamous that there’s even a section on Wikipedia documenting it.

Or let’s consider Reddit as an example. Most Redditors agree that the default subreddits are awful, with r/funny, r/atheism and r/politics being the worst offenders. What do these have in common? They’re enormous — r/funny has more than 5 million subscribers.

If Redditors were one of those dolls where you pull a string and the doll repeats a fixed number of phrases, one of those phrases would be, “The default subreddits are terrible — stick to the smaller subreddits.”

We have this dichotomy, then, where the larger the subreddit, the more it sucks, and YouTube, one of the largest sites on the web, is horrendous. This suggests that the larger an online community, the worse it is.


The natural extension: beyond a certain threshold, adding more users reduces site quality.

The Trouble With Large Communities

Why do online communities get worse as they grow? What’s going on?

Consider the vampire bat. At night, it ventures from its cave, along with thousands of others of bats, and goes on the hunt. The vampire bat — like some sort of comic-book villain — has evolved a special brain region that enables the detection of hot spots on animals (usually goats, its favorite food). It’s a sort of infrared vision.

The bat must feed every two nights, but doesn’t always manage to find a goat. Instead, it often has to rely on the charity of other bats, who share blood after a successful hunt. The bat then pays this forward — sharing blood with those bats when they’re hungry.

As it turns out, bats are pretty decent game theorists. The hunting-sharing cycle is sorta like an iterated prisoner’s dilemma. If everyone shares, we’re all well off, and if everyone is selfish, a lot of good bats will starve, but if everyone else shares except me, great, since I get gallons of blood. To enforce cooperation, the bats implement a tit-for-tat strategy — if you share with me, I’ll share with you next time. This, plus a friendliness clause — sharing with unknown bats — is tit for tat.

Such a strategy breaks down when the share-or-not-share decision is not iterated. In a single shot game, prisoners defect — all the bats will be selfish. For blood sharing among bats to occur, they must frequently interact with bats they know.

Online communities are just like vampire bats sharing blood. I’m nice to my friends, to people I know, because I expect to see them again. That’s sorta what being my friend means. I like you, so I’ll be nice to you, and maybe that feeling of liking is evolution’s way of nudging me with “Hey, you’re going to see this person again. Cooperate!”

I’m not nearly as nice to strangers as I am to people I know. It’s the human condition. Those who claim to treat all beings equally are as naive as a child who tries to catch a rainbow and wear it as a coat.

There is no reason to trust people you will not interact with again in the future. There’s no incentive not to defect. At the end of my last relationship, our interactions became significantly less pleasant as it became more obvious that it was over — I would not have to deal with this person in the future, so why bother going through the motions of kindness?

That’s what happens in large internet communities. The probability that I will interact with any one user ever again on a site like YouTube tends toward zero. I have no real incentive to be polite or to put much effort into anything I say. Even my reputation will remain intact — who’s going to witness it?

In a smaller community, the opposite is true of the incentive structure. I will have to deal with this person again in the future and the stable set of regulars will probably see whatever it is that I do, coloring their opinion of me. Thus, I ought to act kindly and make an effort.

This kindness and effort, these are not calculated responses, not always. Much of it happens outside of conscious deliberation. The same cognitive hardware that evolved to deal with small tribes in the ancestral environment is repurposed for online discussion, and this manifests as emotion and nonconscious behavior — I like people that I see a lot and this pushes me to be more charitable. Or I feel more empathy towards regulars in a community, which affects my actions. And so on.

In summary, then:

  • Communities decay as they grow larger.
  • The development of trust and kindness between two people depends on the probability that they will interact in the future.
  • When communities grow to a certain size, people no longer expect to interact in the future, and thus are more likely to defect — to be petty, mean, aggressive, and to put little effort into their contributions.

Further Reading

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  1. Toby says

    This article is wonderfully written.

    It wasn’t at first clear how this theory could be used to prevent decay, but if pleasant communities are all about repeated interaction, this is actionable — you could try to, say, create a set of smaller sub-communities within a community, or somehow bubble posts of “friends” (e.g. those users you’ve spoken to in the past) to the attention of the user, via a feed ala Facebook, or some other mechanism.

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