Interesting thoughts on the ending and I am one of those that does not mind an ambiguous ending at times. So I guess he might of survived (although with the bite infection may do him in in the end.) or he collapsed and the others did him in. Anyways finally seeing the whole film uncut it was great to get the whole story and watching Whitman's character really get into his going primal ways. Also the way this ended with O'Brien not going to the copter reminded me of the end of a certain TWILIGHT ZONE episode where a character had a chance to leave a place they were surviving in, but just couldn't. I would have to wonder in real life could a human bound so strongly with some environment they could not leave with a rescue party? Interesting thought

patrickdearen-author^
Wow!
Very observant and great post!
I love this movie, BTW. It was one of my Dad's favorites, and I remember so well the baboon scene at the end, when I was watching it on TV, with my Dad when I was a little girl.
I found it on Amazon streaming today and bought it ~ great seeing it again after all these years.
"Much communication in a motion, without conversation or a notion"

It is NOT an impossibility of humans gaining the trust and respect of wild animals and becoming pack leader.
The very stories of TARZAN and MOWGLI of 'The Jungle Book' were based on factual accounts of children or even adults who survive the wilds and end up following a pack or herd and thrive.

Although screenwriter and director Cy Endfield opted for a somewhat ambiguous ending, he provided the audience with clues to O'Brien's fate. First we have Dr. Bondrachai relating that baboon society is a monarchy, and that a king can be replaced only when vanquished by a stronger male. By that standard, troop members would be used to accepting a new ruler. Second, When O'Brien swoons, he doesn't completely collapse. Instead, he drops to knees and hands (with his visible elbow locked) across the dead baboon. This position gives him more the appearance of a baboon than would a standing man. Third, the other troop memberswho had been screaming and baring their fangs immediately before and during the fightgo completely silent at the death of the alpha male, and their demeanor as they approach O'Brien shows none of their previous aggression. As the camera pulls away and the closing credits roll, they gather around him as if paying homage. This is in keeping with the conclusion of the source novel, which unequivocally paints O'Brien as assuming the role of the new alpha male.
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We need to be sure. Quick! Someone who can ask Stuart Whitman.

With respect, there were
not
two endings of this movie filmed, and certainly there were never two different endings shown in different theaters. (And filming two different endings to a movie is really not at all common.)
The only ending is the one seen on the DVD, where O'Brien (the correct spelling of his name, by the way, everyone), having killed the leading baboon, is then beset by the others, in long shot, converging on him. It's not the cleanest ending, but clearly the others are about to kill him.
Besides, O'Brien was badly bitten by the alpha male before he killed him, and baboon bites are extremely toxic not poisonous as such, but so infectious that O'Brien would almost certainly have died soon after anyway.
I suspect, Fingaroo, that, as happens to most of us, your memory of a film you saw 40 years ago has simply become hazy and distorted, so that you think you remember something you never actually saw. I've seen this movie off and on for over 40 years and there is only the one endingwhich is one of the more bizarre conclusions to a film I've ever seen.

As is not uncommon, I think that there may have been two endings filmed/edited. I saw this film 40 years ago and, like your friend, remember an exhausted, bloody-but-victorious O'Brian clambering up on top of a rock after the fight, and all of the other baboons looking cowed. It was clear they had a new leader. But I just saw the DVD and it has the other ending where it can be reasonably inferred that he is killed by the rest of the troop. I like the first ending better because I think it is more in keeping with O'Brian's gradual descent into barbarity.

It is funny, but having watched THE GREY over the weekend, we have the same scenario (and quite an argument on that movies board). Instead of Stuart Whitman battling the alpha male baboon, it is Liam Nesson about to go to war against the alpha male wolf. And the key to that sentence is about.

plus he sort of fell unconscious with his eyes rolling to the back and falling down, saw the film today - so yea, it's pretty much fact they all gathered in to kill him.

The idea that O'Brian would be viewed by the baboons as the new alpha male is preposterous, both commonsensically and scientifically, and presumably the filmmakers (even at the time) weren't ignorant of this, so the ending isn't ambiguous at all. They converged on O'Brian to kill him and eat him.

Very likely they converged to eat him, although one can argue that they did so to eat the dead alpha male. I'm also not sure how a human leader will, uh, take his pick from the female baboons.
Finally, this might help:
http://www.scienceinafrica.co.za/2002/december/baboon.htm
In which case, they probably just ate him.

I think your friend is correct. I remember watching this film as a child and thinking that the baboons attacked O'Brian at the end. I watched it again about five years ago and changed my mind - I now think that the baboons were flocking to their new leader. I think the posting by 'rosscinema' is probably the definitive answer - that the ending is deliberately ambiguous.

I just saw this and the baboon fight is pretty convincing, with Whitman all bloody. Then the camera backs way off so we see the baboons converging on him. I assume they could not really stage a baboon attack, so we are left to assume that is what is happening. I don't think the baboons see Whitman as their leader because they already hate and attack him for murdering several baboons earlier in the film
A TERRIFIC FILM , btw

I think the ending is up for interpretation. I think it's an ambiguous ending.

Thank you. That's how I thought it ended

He did indeed kill the alpha male and one other. After that the camera looks down from the sky as the remaining baboons all go after him at once.