Does choosing different dialogues/actions for Nathan affect the storyline?

In different sections of Uncharted, 4 you are able to pick what Nathan will say or do.

Are these decisions tied to the story, so that what I pick changes what happens or do my choices only affect conversations in the story?

Solution 1:

Having completed the game, I can confirm that the option to initiate a conversation with a character does not affect the story of the game.

These options just give an extra insight into the back story of the characters and are interesting to listen to if you want to find out more about the characters and their story.

edit: Just to add, there is a trophy that can be achieved if you find all 36 Optional Conversations.

Solution 2:

One decision that will have a minor callback at the end of the game, but doesn't impact any story/gameplay (minor spoiler):

At one point, young Nathan can choose to wear one of 3 hats, then he takes a selfie. At the end of the game, you see that selfie again, wearing whatever hat you chose. Nothing changes other than what you see. A character does comment on the photo, but not on the hat.

Solution 3:

You earn a trophy at the end of the game, if you interact with all of the character's dialogues, which is a sense of achievement. Otherwise, it doesn't change the main story at all. However, some of the dialogues are very important in understanding the detailed background to the situation.