  In the past few years, Reddit -- a community-driven platform for submitting,
commenting and rating links and text posts -- has grown exponentially, from a
small community of users into one of the largest online communities on the Web.
To the best of our knowledge, this work represents the most comprehensive
longitudinal study of Reddit's evolution to date, studying both (i) how user
submissions have evolved over time and (ii) how the community's allocation of
attention and its perception of submissions have changed over 5 years based on
an analysis of almost 60 million submissions. Our work reveals an
ever-increasing diversification of topics accompanied by a simultaneous
concentration towards a few selected domains both in terms of posted
submissions as well as perception and attention. By and large, our
investigations suggest that Reddit has transformed itself from a dedicated
gateway to the Web to an increasingly self-referential community that focuses
on and reinforces its own user-generated image- and textual content over
external sources.
