Twitter, long known for its slow and careful evolution of its core product, the tweet, is rolling out a worldwide test that would allow users to downvote replies, a feature that could significantly change how the service works. 

The concept of downvoting posts and comments has been a staple of the Internet for decades, appearing on sites such as Slashdot, Reddit, and Ars Technica. The concept is simple—users who find issue with a post can vote it down.