This is a example of survival of fittest because she didn't adapt. This was because she was to friendly. This is said on pg 14-15 she was being to nice and got killed.
She drowns in the ice they are running on breaks and she falls in. This shows she was not fit to survive in that environment. Which is a example of survival of the fittest.
Buck shows survival of the fittest by killing spits. This is shows survival of the fittest by showing that he adapted quickly enough to survive the fight between them. This happened in pgs 38-40
Spits learned how to survive quickly by using his surroundings and taking Buck's underground house/den instead of making his own. This is on pg 36-37
She was crying because of every one dieing. She couldn't take it and bursted out crying. Which shows she wasn't fit to survive because she was to sensible. This is on pg 65
Dolly get attacked by a pack of huskies and gets rebies. Later he goes wild and Francois ends him by trowing a ax at him. This shows that he couldn't survive which led to his death. This can be found in pos 30-31