I could see that Ape Man representing primal urges, muteness, and even the exploitative nature of using a homeless man (wasn't the character supposed to be homeless?) as an art exhibition to illustrate ideas just to please the rich and feed their vanity.
The irony here is that the rich at that party, who observe with amusement this lowly specimen, may not have been that far off from him. Their own daily muteness comes in the form of ignoring panhandlers and those less fortunate. Their base urges and lusts have never really evolved, despite their formal outward appearance (Christian himself is a sex-obsessed womanizer who doesn't care about their feelings, and only seeks immediate pleasure). And a gathering of rich people chuckling at Ape Man's crude behavior becomes ironic again, when the rich start to pummel him at the very end.
Reminds me of a scene in Scorsese's Cape Fear, when he had Nick Nolte, previously a sharply-dressed and highly successful lawyer, look like an ape at the very end, squatting and muddied and bloodied, and forced to draw upon buried primal emotions just to survive. Perhaps the Ape Man is always there.