IRL, bears have something very similar to D&Ds Rage. As I mentioned earlier, the term "berserk" is from the Norse for "Bear shirt". To put on the "bear serken" (bear shirt) was to try and invoke the spirit and fury of the bear. It was a literal thing, a shirt made of bear fur.
There was a case of a man who was out hunting. He saw a bear, took aim and fired. The bear was hit, but instead of falling down and dying, he went into a rage, charged the man and killed him. It was later found that the man's shot had been fatal: He'd hit the heart, but the bear, so pumped up with adrenaline at the sudden attack, didn't know it. He had enough in him to complete the charge and the attack before he fell.
Wolverines are also known for their berserk fury when they fight. That's why the comic book character was named after one.
Most animals in nature will pull out of a fight if they're getting badly hurt. If the price of victory is later death due to the inability to hunt or fight, it's not really a win. Bears and Wolverines don't seem to get that. They go into a fury and they don't know how to stop.
So yeah, Rage, as used in D&D, is based on something in the real world.
Esoterica aside, I have a question about Reach weapons and Large size.
Most large creatures (but not the Brown Bear) get Rach. That is, they have a 10 foot base and 10 foot reach. Bears havd 10 foot base and 5 foot reach, which is fine.
Normally, when you us a Large Reach weapon, such as a character under Enlarge Person using a ranseur or long spear, their reach extends to 20 feet. That's what the rules say on the subject anyway. They threaten the 15 and 20 foot squares, while the 5 and 10 foot squares are inside the weapon's threat range. (Spiked Chain is the exception, it threatens all the way in.)
But what happens if the Large creature doesn't normally have that 10 foot reach? Does the Large weapon still go out to 20 feet?
Inquiring bears want to know!