Now look at our history. For hundred of thousands of generations, our forebears ate opportunistically, and remained in almost the same state of advancement for millenium after millenium. They doubtless lived short lives, cut short by misadventure and predators, with a range of illnesses mostly caused by lack of nutrition, and relatively few diseases such as obesity, inflammatory illnesses, or cancers. This was a kind of Golden Age you could say, where not much changed, you knew where you fitted into the scheme of things, you foraged for your food, and that was it for the next couple of hundred generations. But also, of course, it wasn't like those ancestors could appreciate that they were in a Golden Age, because they were pretty much stupid animals. The ancestors of dolphins and octopuses must have been gleefully looking forward to dominating the Earth.
But things change. Somewhere, some pre-human a bit dumber than all the others ate something none of the others had tried to eat before. And okay - he died, because funny mushrooms are seldom funny. But if there's one thing history teaches us, it's that there are a lot of dumb ones in any given species. So another really dumb pre-human found itself strangely attracted to, and ate, some bird's eggs it found. And it discovered that it wasn't as hungry, could spend some time picking among the forage for "better" foods. Maybe one of the smarter ones noticed, or maybe this particular one just lived longer because of its habit of eating eggs, and so managed to still be alive to impregnate or be impregnated when its contemporaries had long succumbed to starvation. No matter - the point is that a particular trick of the genes had been captured in a new generation, and now found an attraction for eggs to be normal.
Now there's a generation of pre-humans who don;t need to spend the entire day foraging and scrambling for food, that leaves time for other things. Copulating and breeding can only remain attractive for so many hours a day... (And besides it was breeding all these freakish critturs that ate other animals, their eggs and young, and selectively higher-value forage plants!) What to do with the other few hours of the day? Well, once you'd dozed in the sun a while, pretty much you'd start talking about the weather...
BTW I don't know if it was chickens or eggs or minivelociraptor drumsticks, and I emphasise that this did not happen overnight, it happened over hundreds and perhaps even thousands of generations, and in only a small subsection of the whole species, maybe just one particular valley. The thing is that whatever powers evolution, whatever forces are at work there, it resulted in that particular population slowly becoming tolerant of the change in their diet, and finally, their bodies were adapted to it and required it as part of their normal functioning. That particular branch of the species didn't need to spend as much time hunting down food and could afford to spend more time - well, thinking might be a good term for it.
Eventually, out of all those different branches of pre-humanity that had adapted to different diets (and now you can see why it initially took so long) several emerged that also had a strange compulsion to hoard foods...
Also note that in each case, the evolutionary change that provided benefits was the one which prevailed. That's how evolution works - it doesn't "favour" chickens that flee and hide if they see a hawk-shape in the sky. It's just that those chickens that don't run and hide get eaten, and so don't pass on anything to future generations...
The most important thing for us to take home from the above is that our bodies are superbly adapted to the food we eat. Provided it is food that was introduced 7,000 years or longer ago. Any newer foods and ways of preparing food our bodies are still in the process of adapting to.
Let me give you a most brutal example: Our foods for the last 200 years have increasingly contained additives and extenders and modifiers. These may provide us with the benefit of more food being available more of the time, and thus allow us to breed more and more humans with more and more non-food-gathering time in their hands. But they are not suitable for our bodies, and cause disease and illness. Those that can tolerate this range of poisons will live longer, and pass on some of those traits. The rest will die of food-related illnesses and not pass on as many genes. Look around you at the number of obese people with diabetes, stomach bowel and colon cancers, heart diseases and so forth - do you really think this is the natural lot of people?
So - if you're one of the five people in the whole population whose bodies tolerate all those additives and want to pass on that to the next generation, go ahead. It will be a valuable thing for future generations, say in the next 1,000 years or so. For the rest of us, there are only two choices, either to become a statistic and one of the negative shapers of evolution, or else do the right thing by ourself and start really looking at every skerrick of food we put into our bodies.
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