Reddit's tone decays because there is nothing new left to like

A new paper in PNAS by professor of psychology Joshua Conrad Jackson and colleagues analyzed more than 2 billion comments from 2,150 Reddit communities and found that both threads and communities became more negative over time, with semantic differentiation driving the trend: negative comments were more semantically unique from what had already been said ^[1][2][3]. That matters for anyone operating a community product, because it puts part of the tone problem in the participation incentive itself rather than only in feed ranking ^[4][10].

Jackson is explicit that he is not exonerating ranking. He describes feed-ranking algorithms as picking up divisive content that holds attention, angers people, prompts them to post their own divisive content, and generates ad revenue in the process ^[9]. The paper, he says, was "kind of a side quest" to test whether conversations would still turn negative in the absence of those algorithms ^[10].

The observational results are the load-bearing part. Reddit as a whole has become more negative over time; the longer a given community exists, the more negative it becomes; and the longer a comment thread continues, the more negative that thread becomes ^[11][12][13]. Jackson says this is the first time that has been shown ^[14]. Two further predictions held: threads that start more positive turn more negative, because the positive comments are taken at the beginning, and larger communities get more negative, because the information ecosystem is more crowded ^[15][16].

The mechanism rests on an asymmetry. "Negative information is just much more diverse than positive information," Jackson said ^[17]. His example: on a thread about Christopher Nolan's "The Odyssey," the top comment might be "I liked it," after which there is little else to add, so standing out means naming something you disliked ^[18].

Then the causal leg. In an experiment, users primed to be unique posted more negative comments than users primed to conform ^[19]. Jackson notes the participants were not incentivized to be negative; negativity was a side effect of trying to say something unique ^[20]. Prior work had found negativity can be a conscious choice because people see it rewarded; this paper adds the indirect route ^[21].

Two constraints on how far to carry this. Jackson stresses that communities do not fall off a cliff of toxicity, and that the stereotype of social media is worse than the reality ^[22]. And the reported analysis is limited to the first 50 comments in a thread ^[23].

For operators, the practical implication is that the usual levers sit next to the actual constraint rather than on it. Moderation policy and ranking changes act on what gets seen; the finding is about supply, specifically the shrinking stock of things not yet said. On that reading, growth is a tone variable, since the crowding effect scales with community size ^[16], and any surface that lets a user register agreement cheaply is competing with the incentive to differentiate by criticising. That last point is inference, not a result in the paper.

Worth watching: whether the pattern holds past the 50-comment cutoff the authors used ^[23], and whether the differentiation account transfers to other forms of media, which Jackson was asked about in the interview ^[24]. Also worth watching whether product teams treat this as an excuse. A finding that negativity has a non-algorithmic source does not make the algorithmic source smaller, and Jackson's own description of the ad-revenue loop is the more expensive problem ^[9].