Note: I'm not going to use the word "heroine." All instances of the word hero apply to all genders unless specified otherwise.
We discussed the need for heroes to have human qualities of compassion and care, and possibly to engage in personal self-sacrifice. This led us to discuss how a sociopathic hero (such as Sherlock Holmes) is most effective when framed by a supporting cast with these compassionate qualities, allowing the sociopath to keep an element of mystery without ruining the sense of caring.
The goals of heroes must align in some sense with the audience's goals.
Bad guys have to be worse than good guys (good guys need not always be good). Context is everything.
Heroes need not be effective individually, but may be more effective in groups, as in Guardians of the Galaxy. Superman suffers, narratively, from his overwhelming powers, especially as we continue to write stories about him. He doesn't make a good team member. He is something of a prototype hero. Groot, by contrast, starts out seeming useless and then becomes more and more amazing as he develops abilities.
Animal heroes, incomprehensible heroes like R2D2, and "strong silent type" heroes are similar in that they are mysterious and often need translators. A silent and mysterious hero lets the readers/audience project emotion onto them. They speak with their actions, and sometimes with internalization in close point of view narrative. Silence may also imply a past they can't talk about, or be a "sign of badassery" (Thanks for that phrase, Che Gilson!).
Heroes have a kind of simplicity when it comes to knowing the right thing to do and not letting other motivations or problems get in the way of them doing it.
Heroes often get thrust into impossible situations, and this helps readers relate to them because people get thrust into difficult/impossible situations also, regularly.
Heroes are known by their actions. These actions lead to results that are judged as "good" by the people around them and by the reader or audience. "Good," however, is culturally defined. Thus changes in worldbuilding can significantly change the nuances of good action done by the hero. Motivations can complicate actions, while silence tends to magnify action.
Are female and male heroes different?
Certainly they are portrayed differently. Chihiro from Spirited Away is kind, reliable, and always cleaning things. Miyazaki often has female heroes cleaning things as a sign of their strength. Pazu from Castle in the Sky runs errands and fixes things but doesn't clean. The trend toward the Strong Female Character tends to pull female heroes toward the stereotypically masculine, aggressive side, but we shouldn't neglect the importance of feminine qualities. Cleverness and trickery often work for a female hero, much as for a male hero who does not possess overpowering strength.
Evil is typically depicted as being overpowering, but dilute (lots of soldiers, none of whom can aim, while the hero never misses). Heroism is often distilled into a single character, but the qualities of the hero can also be distributed across the team (as in the Guardians of the Galaxy reference above).
More recent depictions of heroes spend a great deal of time exploring gray areas. This could be an interest of more mature writers who have more life experience dealing with ambiguity, or it could also be a historical trend.
As I mentioned, more detail and examples can be found in the video, which lasts roughly an hour. I've tried to report this in order, so if you want to click through and find a piece of the discussion, you'll have a rough sense of where it may occur.
Thanks again to everyone who attended! You're all fascinating to talk to!