I understand food wasn’t always so abundant, and humans were well served to store excess consumed energy as fat for later use. What I don’t understand is why the body keeps storing fat to the point where a person becomes morbidly obese and it puts their entire health at risk. Why isn’t there a point where the body just let’s the extra calories pass through without saving for later?
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I think it’s that bad food is stopping the body from following its natural fat path. Fat should store in your buttocks first but with the food we eat it’s storing at the belly. The toxins in food are stopping the body from processing fat properly.
Cause there’s never been a point in human history where food was so abundant that we could eat enough to jeopardize our health, at least not on a macro scale. Thus, there was no selective pressure to develop any mechanisms that “limited” the amount of fat our bodies could store. Fat was only ever a *good* thing for us and so we only ever evolved to store as much fat as we could. Fat has only become a detriment to a significant portion of our population in the last 100 years or so which is not nearly enough time to select against traits that cause fat to grow.
We evolved when there wasn’t much stuff to eat. So our bodies got good at staying alive on not much food.
We haven’t (yet) had time to evolve to deal with too much food. So we get fat, and unhealthy because our bodies aren’t set up to deal with it and still act as though a famine might be coming.
Give it some thousands of years, and we may well evolve to deal with too much food.
Humans didn’t evolve in an environment where abundant food was a threat to reproduction. So long as humans are able to reproduce before the storage of excess fat becomes a problem, there isn’t really any evolutionary advantage to not storing fat. Even after the rise of agriculture, famine and nutritional scarcity have been relatively common until about 200 years ago.
There are a few reasons.
The main one is that there was no evolutionary advantage to having an upper limit on fat storage until very recently, and evolution is not survival of the “fittest”, it is survival of the “good enough to pump out at least one round of kids.”
Secondly, the cells that make up fat tissue have their own survival drive. A human is just a collection of single cellular colonies. Each one of those colonies has a survival drive of its own.
The body overrides those survival drives with chemical signals and occasionally direct intervention from the immune system, but if resources are abundant cells will do what cells do and replicate.
Just very, *very* basic evolutionary biology here.
Evolution doesn’t choose anything. Natural selection is a dumb phrase.
Instead, it’s better to think of it as “if a mutation causes an individual to be worse at surviving, the mutation won’t carry on to future generations.”
Except that’s not true either. Cardiac disease, dementia, and liver failure tend to be fairly common, so shouldn’t they go away?
Well, no. Because the important bit is “carry on to future generations.”
If your family has Alzheimer’s, it’s likely not going to impact how many kids you have (and thus how common it can be in society) because it doesn’t make it harder to reproduce.
As humans live longer, as medicine solves other problems, cancer increasingly becomes a common cause of death. Cancers we don’t have much experience treating, because they don’t really happen in young and healthy people. And there’s no genetic pressure *not* to get these cancers, because they’re typically not happening early enough to interfere with reproduction.
Any disease that causes reproductive issues (physical ailment, sterility, or obviously death) before an individual can reproduce doesn’t carry forward.
So onto body fat.
Excess body fat has no biological “stopper” since it doesn’t (biologically, ignore social aspects) impact reproduction. It’s *possible* for a person to be extremely obese through childhood which causes reproductive difficulty into adulthood, but the last few decades have been the only time in the development of our species where there was enough surplus food for that even to be possible. The majority of people that get very obese won’t have severe complications until after childbearing age.
Because evolution doesn’t have sentience and isn’t for our benefit. We can intervene, but ultimately, the traits we develop will happen whether or not they’re good for our species, and they’ll either survive or they won’t. We don’t have opposable thumbs because they help us build tools – we were able to build tools because we have opposable thumbs. I find it interesting how evolution is typically described through a creationist lens.
Edit to answer your actual question instead of just my reaction to pop-evolution:
The traits species develop can be pretty random. If individuals of a species survive long enough to reproduce, then they can pass their traits along. If there’s a genetic mutation that stops one from reproducing, it can’t be passed along. It’s not as simple as “good trait gets passed along” and “bad trait is bred out”, but the point is that evolution is more about genetic mutation than it is about what helps us.
We focus on our beneficial traits because they helped us survive, but there are infinite species that couldn’t make it.
We happened to have traits that allowed us to survive on earth. But we’re not actually the main character. There’s no omnipotent force, and we’re not entitled to survival.
The fat storage example is just how our genes react to this new environment. If some humans have genes that allow them to optimize fat storage, then it’s available to be passed along, but how would you even know who has those genes? Obesity doesn’t typically become a health problem until older age, so there’s plenty of opportunity to reproduce before the fat storage is a problem. Most people are going to reproduce with who they want to share a life with instead of for their genetic makeup.
With scientific advances, we can edit genetics, but we still have to work with what’s already available. We can’t yet just decide what would be best for us. We can add blue eye genes to a designer baby, but we can’t give it teleportation abilities.
We can only pass on genes that we have access to, and seeing as there’s no designer, there’s no one to give our feedback about our bodies to.
the body has homeostasis which adjusts all the systems to accomodate problems until a fatal meltdown, like a heart attack. The computer in your car does the same thing. Evolution in animals takes a very long time because a generation is so long. Plants have evolved to have lower and lower saturated fats. Palm oils are high in sat fat and have existed since just after the dinos, things like canola oil are low in sat fat and are much more modern. Plants have realized that fat saturation causes more plant damage (because it tastes good to the animals) so they evolved to not taste as good. Humanity evolution will slowly kill off the bodies that suffer most from obesity and leave the ones that tolerate it better.
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