A picture is worth a thousand words. So, I'm gonna just let the photo do most of the talking. Ever since this photo was published it has gone viral everywhere. Read about this news story at National Geographic and an in depth explanation of the photo here.
This photo is not surprising because it is well documented that chimpanzees mourn the death of their own. I guess the reason why it went viral is because the sheer volume of individuals mourning the death of this female chimpanzee. It looks almost human-like and behaviors that are human-like tend to evoke empathy in humans.