How are the two humans selected to repopulate the world after Ragnarök?

Question

According to Norse Mythology, Ragnarök is a series of future events that means great disasters for the world and the end of many important and powerful gods:

In Norse mythology, Ragnarök is a series of future events, including a great battle foretold to ultimately result in the death of a number of major figures (including the gods Odin, Thor, Týr, Freyr, Heimdallr, and Loki), the occurrence of various natural disasters, and the subsequent submersion of the world in water. Afterward, the world will resurface anew and fertile, the surviving and returning gods will meet, and the world will be repopulated by two human survivors . Ragnarök is an important event in the Norse canon, and has been the subject of scholarly discourse and theory.

_{source: Wikipedia article on Ragnarök}

After Ragnarök, it is said that the world will be repopulated with two human survivors. How will these two human survivors be chosen? Will they be randomly chosen or selected by the remaining gods who didn't die during Ragnarök?

Answer 1

The two human survivors are Lif and Lifthrasir. They live through Ragnarök by hiding in Yggdrasil before the great battles, supposedly in Hoddmimir's wood. Apparently, Vafthrudnir told this to Odin in a prophecy.

They are mentioned in verse 45 of Vafþrúðnismál:

"Líf ok Lifþrasir,
en þau leynask munu
í holti Hoddmímis;
morgindöggvar
þau sér at mat hafa, en þaðan af aldir alask."

I don't know Icelandic, but this answer gives me

45. Lif and Lifthrasir
    lie hidden
    in the grove of Hoard-Mimir;
    the morning dews
    they shall have as meat,
    from them generations will spring.
    

_{source: http://www.germanicmythology.com/PoeticEdda/GRM27.html}

This verse is the source of the prophecy to Odin.

It seems that the two humans were, though prophesied, simply random people who happened to find a safe (and sacred) place to hide.

For the reasons why Yggdrasil was safe, see How is the Hoddmímis holt able to protect humans from Ragnarök?