What does the phrase "the dominant primordial beast was strong in buck" mean?

London begins this chapter by stating that the "dominant primordial beast was strong in Buck," meaning that the primitive will to survive was now the primary factor in Buck's life. ... This arouses the "beast" in Buck, and he springs upon Spitz "with a fury which surprised them both."

Please, what did you get 1-10???

Your answer would be a , i hope you do very well