Medical research has demonstrated that individuals who have higher levels of testosterone are more assertive, dominant, and competitive. however, as the social psychologist allan mazur noticed in his study of chess competitions, testosterone levels rose in chess players before a match and then rose again in the match’s winner, but they fell in the loser. what does this suggest about the origin of gender?

You didn't give us any options, but I managed to find some on the Internet.
It is either one of these (depending on which one you have available): Gender comes from an interaction between nature and nurture OR Gender comes from an interaction between biology and social contexts. 
In either case, it is important to note that the interaction between our surroundings and the inner workings of our bodies is important when it comes to gender and distinctions between genders.

Reward is synonymous with positive reinforcement only