Techniques are provided for selecting a diverse mix of content items that may be displayed to a user. Content items such as user-generated events are received from a variety of sources. One or more content items are added to a set of content items based on a diversity of characteristics. The diversity of characteristics for the one or more content items may be calculated by measuring a diversity of characteristics of the set as if the one or more content items were added to the set. Content items that produce a greater diversity are selected for addition to the set. The set is displayed to the user, who is provided with a more meaningful mix of content due to the greater diversity in content.