Not true. You’re assumption is that we are different from our past. We are not. The " tortured hypthetical situation" is the same for us, evolutionarily speaking, as it was then.
First, as far as evolution is concerned there probably isn’t much selection pressure against it. Humans have been cooperative creatures for a long time; being momentarily disabled is seldom fatal, especially if you can predict and avoid the situations that cause it. It’s still a disadvantage, which is why most people don’t faint that often. The most dangerous time for a human to black out from pain without being helped would be a battle, and severely wounded people in a primitive culture are likely doomed anyway ( no antibiotics, and not much mercy ).
Second, I read an article years ago that claimed a great deal of fainting is caused by people who have a lacking/defective portion of the nervous system; the parasympathetic system IIRC. The article claimed this causes problems in keeping blood flowing to the brain under stress; for example, if they stand in one place without moving ( like in a military formation ) the blood will pool in the legs, reducing pressure in the brain and causing a faint; in most people the arteries and capillaries in the legs would reflexively squeeze down, forcing the blood back up. Basically, it claimed that someone with this problem will faint under a wide variety of circumstances.
I am making no such assumption. The point is that the tortured hypothetical situation is a tortured hypothetical situation. It is not the normal situation upon which selective forces are operating.
Think about it like this. Possums play dead when confronted with predators. Sometimes a possum playing dead will get eaten. The problem with your ‘reasoning’ is that you are claiming that playing possum could never have evolved because it sometimes increases the risk of death. What you are totally failing to comprehend is that it often decreases the risk of death.
The exact same thing is true of the fainting response, or the pain response in general. Under extremely rare conditions it is hypothetically possible that any pain response can result in needless death. But under extemely common circumstances it can prevent needless death. Thus it is selected for.
Hopefully that added example will help you understand that no strategy is ever risk free for all hypothetical scenarios. It is simply a question of whether the benefits outweigh the risks in the real world. That’s an easy point for laymen to fail to grasp fully.
That can’t work. If the capillaries and arteries constrict you get less blood flow to that area, but it can’t force blood back anywhere. If the capillaries and arteries dilate then you get more blood moving into the tissues and more swelling, but still no blood being forced anywhere. The problem is that fluid moves back up via the veins and lymph vesseles. Those lack any real muscle and can’t squeeze anything. They are operated themselves by external pressure form the skeletal muscles. You can play aorund with the parasympathetic system all you like but skeletal muscles are under voluntary control.
I understand the endorphins and adrenaline explanation, but what if it is a delayed reaction? I twisted my ankle right before getting on the school bus, but I managed to limp up the steps, down the aisle and into a seat with nothing but some major pain in my foot. It was a minute or two later, after I sat down, that the urge to black out came. I started to sweat, got some intense nausea and had to lean against the front of the next seat to keep from falling over. Why would my reaction have been delayed? I was calm, so the adrenaline didn’t seem to be pumping.
Adrenaline will normally prevent you from passing out. As I pointed out above, adrenaline raises blood pressure and stimulates heart action, exactly the oposite of the effects that cause a faint. When you take a hit a first reaction is commonly an adrenaline burst which prevents immediate blackout. If you’re still having difficulties after the adrenaline wears of then you can get into difficulties.
Once again though, the exact causes of fainting aren’t well understood. People can pass out without actually experiencing much pain or being squeamish. There seems to be some sort of nervous networking involved but it’s poorly understood. Part of that may be that adrenaline tends to dull pain perception anyway, so the brain and vagus nerve may be getting pain signals but the conscious brain isn’t interpreting them as such.
No matter what the veins do, if the arteries/capillaries contract there will be less space for blood in the legs and it will be forced out of them. Besides, veins don’t need to squeeze, since they have valves to keep the blood from flowing back.
It simply doesn’t work like that. If the arteries/capillaries contract there will only be less space for blood in the arteries/capillaries and as a result less inflow and higher blood pressure. That’s all. It won’t promote outflow in any way at all. There will still be just as much intracellular space for fluid, and that will result in swelling and loss of blood volume. There will still be just as much space in the vains and lymph vessels.
I think what you’re overlooking is that the arterioles are leaky pipes, they aren’t remotely watertight. Imagine that you have a reticulated water supply with a pump at the reservoir and a leaky pipe at the working end. In this analogy constricting the cappilaries is the equivalent of fitting the system with a narower pipe guage between the pump and the leaky pipe. That will result in higher pressures at the leaky pipe. But because the pipe is leaky higher pressures don’t result in lower losses from the leaky pipe, in fact it usually results in more loss because the pressure forcing the water out is higher. With a leaky system of this type increasing inflow pressure can’t possible enhance outflow, in fact quite the opposite, the less you get in the less you put out.
A simple question: You claim that constricting the arteries and cappilaries results in a greater return of fluid from the extremities. Why then is oedema (fluid buildup in the extremities) a common system of hypertension brought about by constriction of the arteries and cappilaries?
Yes, but the important point is that the valves stop the blood flowing back after it has moved forwards. They don’t actually move it forwards. Forwards motion relies entirely on skeletal muscle action and postural changes, both of which are under the contrl of the volountary nervous system.
No, not a wuss (or at least no more than me)
I had all those symptoms after stubbing my fingers trying to catch a basket ball at school. I passed out completely however and woke up with a painful back and head :smack: