I vividly remember a scene from a short story (?) I read back in the sixties or seventies, and am trying to remember the publication and title. If it sounds familiar to you, please post.
The scene is set in the distant future after mankind has slowly spread all the way to the far side of the galaxy, the core zones being too hostile to life (energetically). In all that time, we have never encountered another star-faring race. We have been modified slowly by the course of evolution over the millenia.
As the scene opens, it appears we have finally had a first encounter with another civilization. There is a meeting set and gradually dialog is established. The twist comes when it emerges that these creatures are, in fact, also the descendants of Earth modified in different ways during their slow passage the other way around the galaxy. We have proven that we are, indeed alone.
The story ached with pathos at the loneliness of being the only intelligent species in existence. (In terms of evolutionary theory, this would likely make us a ring species.)