1. A method comprising: at a computer system having one or more processors and memory storing one or more programs: sending messages in a first set of conversation messages for display; selecting, without user involvement, a second set of conversation messages by: parsing a hierarchy of sets of conversation messages including the first set of conversation messages and the second set of conversation messages, or determining that the second set of conversation messages is similar to the first set of conversation messages; wherein a combined number of messages in the first and second sets of conversation messages total at least a predetermined number of messages; and sending messages in the second set of conversation messages for concurrent display with the messages in the first set of conversation messages.