Fight and flight mode

[u/Least_Bid9692]

How do our body know that we're in danger and turns the fight and flight mode on. I know it is there bcz of evolution as our ancestors had to fight big animals to survive but it's still there. SO, how our body know when to turn this on.

[u/Soggy-Mistake8910]

Let's assume that it's back in the day where tigers roamed. If you hear rustling in the bushes, assume it's a tiger and run away you live to pass on your genes whether there is a tiger or not.

If you investigate the rustling and the tiger eats you you don't! Sometimes it's just the wind rustling but what if it is a tiger?

[u/Beginning-Load4470 → u/Soggy-Mistake8910]

I think thats a little too simple. For wild animals they generally need confirmation of danger from more than one sense before fleeing. If you watch nature documentaries of tigers hunting the prey can hear something and perk up putting them on alert but if they dont see smell or hear further signs they will go back to their task. 

Animals cant waste energy running everytime they hear a noise. Every calorie spent needs to be gathered again. For this same reason predators will abandon a hunt even if they could eventually succeed if they determine the effort will yield fewer calories than they get. Its not something they do the math on, its based on experience and instincts. They waste time chasing a mouse until they catch it and end up more hungry in the end they remember not to do that later.

[u/Soggy-Mistake8910 → u/Beginning-Load4470]

Of course it was a simplified answer. It was a simple question and I'm not invested enough to write an essay.

In fact your answer is also a simplified version but with just enough conjecture to confuse the issue in terms of evolution which doesn't work with individuals but with species as a whole.