When differences exist between the genders, what does the novel suggest are the causes?
In all of Jane Austen's novels whenever a difference comes up between the genders the causes are almost always associated with the historically social role that genders would be expected to fulfill.
When males make decisions in the story you can see how every woman accepts it. Anne was an exception, but the rest of the females in her family would take Sir Walter's word as law.
When Wentworth came back he was upset with Anne for her previous rejection and yet she could not approach him directly to talk it over. It was an act of congress, basically, for a woman to make a point to a man.
Now, the novel suggests that the reasons for all this are simple: Those were the rules, the social roles, in Regency England. You could not break the protocol, nor try to create new rules. This was the simple truth and women were second class citizens that could have not changed anything.