"His cunning was a wolf cunning and wild cunning."
"Buck held steadily".
In this image it shows survival of the fittest because Buck and Mr.Thornton are trying to survive by them looking for a place to stay during the harsh weather. Also it shows that Buck is brave and he is like a wolf because he fights like a wolf. Also if something is in his way he will sure move it.
In here it shows them going to another place. Buck has to get used to adapting more often, and running more often because if he doesn't then they are going to leave but because they need someone to be good at running and being brave like a wolf and Buck is starting to become one, and act like one.
"But he is not always alone."
In this image it shows the Buck will never leave Mr. Thornton side as he was laying/protecting Mr. Thornton. Buck is really brave because if he see's something or hear something he is willing to see and if it is someone unfriendly he would risk his own life for Mr. Thornton life. That is how much love Buck has.
In this image they are at a some little village. They stopped there to get supplies that are needed, and also to rest a little bit after the long journey . Also Buck shows survival of the fittest because they need food and water to survive and protection which they already have.
In here is where it all happens. In here is when Buck had notice either he dies or he kills someone. Buck had been to late as he saw Mr. Thornton laying on the ground covered with blood.
In this image it shows survival of the fittest because know Buck has to survival by himself and had to let go to Mr.Thornton's death. Buck had to adapt to another life.