Is Instagram the new snapchat

Instagram has recently updated its system to include stories on a persons profile. Many argue that they stole this idea from snapchat. In the book Where Good Ideas Come From by Steven Johnson he introduces the idea of the adjacent possible. The adjacent possible is the process that ideas are influenced by other ideas. Instagram may have been influenced by Snapchat but the ideas seem way to similar. Has Instagram plagiarized snapchat? What do you guys think about this? Should Snapchat fight back for what was their idea or should they leave it alone?