Why 'Best Actor' and 'Best Actress' and not just 'Best Actor'?

Why do we have a seperate award for male and female actors and not just one for the best actor?
Why not also seperate by race, sexuality or age?

Or, on the opposite side, why not a category for Best Directress and Best Editoroine?

Short but real answer - tradition and culture.

And the odds of the acting branch of the Academy voluntarily giving up half their shots at an Oscar are pretty slim. (Which I suppose is a slightly longer version of ‘tradition’ from the previous answer.)

By and large male actors are expected to play male roles, and female actors are expected to play female roles. I’m sure we could make a long list of exceptions, but still most women will never have the opportunity to (nor do they necessarily want to) portray men in principal roles in major motion pictures, and vice versa, no matter how talented they are.

Writers and directors may, for various reasons, end up working with material related to their gender, but they don’t have to. If Nora Ephron wrote a great script about manly smoke-jumpers battling an oil-rig fire on the North Sea, it wouldn’t go unmade just because she’s a woman.

You would have had a stronger case for separate ethnic-group categories 30 or 40 years ago. While color-blind casting is far from a universal reality, it is very common these days to see casting calls that say “submit all ethnicities” or don’t specify ethnicity. By contrast, almost every speaking role, down to the one-liners, have a gender attached.

Age is more fluid and harder to pin down than gender. The vast majority of actors fit easily into one of two genders, but how would you categorize age? How many divisions would there be? Would you go by chronological age, which is largely irrelevant, or apparent age, which is actually what determines casting? Then of course you run up against the fact that although it’s harder than it used to be to keep an actor’s actual age secret, it’s not necessarily something that they or their publicists want advertised on the Oscars telecast.

ETA: Most of the above relates to the fairness of having separate gender categories. Of course there are commercial considerations as well. Because the acting categories are considered among the most glamorous and valuable (how many people tune in to the broadcast to see who wins for best sound or buy a DVD because of an editing award?) it behooves the Academy and the studios to have more of them.

Actresses have been very clear in calling themselves “actors”. It has been going on for a few years now. If it goes on long enough, it may justify eliminating the actress category. Wont that get noisy?

TWDuke pretty much said it all.

At least actresses have a category of their own. The real injustice is how the Best Actor award is a de facto Best Dramatic Actor award. A comedic actor has virtually no chance to win it and has no compensating award he can compete for.