I brought this up years ago in another thread and got some interesting results.
http://www.martialtalk.com/forum/showthread.php?13189-I-could-beat-the-british-a-boxer-and-your-best-knife-fighter&highlight=
Basically, fighting is probably the same, although it is effected by environment. Technological advances, such as firearms, and cultural trends, such as the popularity of MMA and BJJ by extension, all have an effect on how average people fight. So while anyone in the last ten thousand years could have worked a straight arm bar from the mount, it's probably more likely to happen in a bar fight today than it was in a bar fight two hundred years ago. And you could only shoot someone with a pistol over the last few hundred years, so that wouldn't even have been a consideration before.
And of course, athletes have access to better training methodologies, sports science, and nutrition, as well as better drugs, so their performance will continue to improve along with those aspects. A stronger, tougher, faster, smarter, healthier fighter will be more effective than a starving caveman with an infection.
Most people don't actually have any training in fighting. So if they get attacked, they act on instinct. Their brains try to mimic whatever their subconscious
thinks fighting is. So if boxing is the most popular combat sport you're more likely to see punches. In kicking cultures you see more kicks. But those are just civilians. They aren't really fighting, their just reacting.
Fighters train. And they'll fight the way they train. So when the training changes, the fighting changes. When I started kenpo we never even discussed ground fighting. For probably five or six years it really didn't even exist for me. Because no one ever brought it up. Looking back, it seems strange, but there was a hole in my mind that I didn't even know was there. Now that I've been exposed to ground fighting and spent time practicing it, it's a significant part of my method. I don't always intentionally go to the ground, but if I choose to or I end up there, I have many options at my disposal now. My fighting changed, because my training changed.
In local cultures that don't allow firearms, we see more knife attacks. That's a change.
In local cultures that emphasize the individual we see more "one on one" fights, in local cultures that emphasize the clan or group we see more gang fights. That's a change.
In local cultures that see the head as the vessel for the "person" we see more strikes to the head, in local cultures that see the body as the vessel for the "person" we see more strikes to the body. That's a change.
Fighting is a part of the human experience. It is affected by all the same things that humans themselves are. Weather, environment, circumstances, technology. We invent bullets, so we invent kevlar, so we invent kevlar piercing bullets. It's always an arms race and it never stops.
Individually, we are all just rediscovering the same things that have been discovered by others before. I haven't seen anything truly new yet. In fact, the more I look in to the history of combat, the more techniques I see demonstrated hundreds and thousands of years before I ever learned them.
I think the next truly new fighting techniques will come from either transhumanism or space exploration. Fighting an enhanced or altered human would be something new, and fighting in another gravity would be something new. Other than that, it's like you said. 2 arms 2 legs. I don't think there's anything new, only things that are new to me.
-Rob