Our brains today are remarkably similar to those of our ancestors 100,000 years ago. We're not actually much smarter than them (if at all), but we stand on their shoulders in terms of accumulated human knowledge. Our brains and bodies are adapted to survive in the savannah, not the city.
When making it through the winter was by no means certain, some adaptations were key to surviving long enough to pass on your genes to the next generation. If you could immediately recognise calorie-dense food by some mechanism - let's call it taste! - you'd know that was the good stuff. If your body was good at storing fat as a long-term energy source, you'd have a better chance of making it to the spring. Dropping dead at 50 of a heart attack (even if that were possible on stone age diets) wouldn't bother evolution - had kids, genes passed on, job done.
Our physiology makes it very clear that we are herbivores. Check out Milton Mills for a full discussion, but in brief, actual omnivores are very rare in nature. Some carnivores adapted to eat small amounts of plants (for example bears and raccoons), while some herbivores did the opposite (gorillas and chimps sometimes eat small handfuls of insects). Carnivores have sharp claws and teeth, their jaws are structured to rip flesh, their stomachs are large [2], their esophaguses are wide to swallow bone and gristle without choking, their stomach acid is very strong to dissolve that bone and gristle and their digestive tracts are short to pass out the nastier undissolved bits of animal as soon as possible. Herbivores are basically the opposite. No claws, jaws and teeth grind rather than tear, smaller stomach, narrow esophagus, weaker stomach acid and longer digestive tract. By every one of those measures (and many more), we're herbivores.
Clever monkeys that we are though, at some point we figured out that while we struggle with raw meat, and can't eat rotting meat at all - unlike an actual carnivore which has no problem with rotting meat, that stomach acid again - cooked meat tastes great and stays down. Maybe someone came across a burned carcass from a forest fire and thought "mmm, barbecue". Technological innovations like fire and the stick (image below, Gary Larson of course) helped us to occasionally consume an excellent source of calories and saturated fat that could make the short-term difference between survival and extinction - for both the individual and the species.
I do say occasionally though, and that's what I mean. Our Hollywood picture of organised caveman hunts providing racks of mammoth ribs three times a day is off the mark. Even for true predators, hunting is an inefficient way to sustain yourself (hence the large stomachs and ability to eat rotted meat). Early men most likely couldn't do much more than pick off the occasional sick animal that predators didn't find first, and then had to face significant danger protecting their prize from those predators. Modern notions that hunters actually ran their prey down in marathon jogging sessions are rightly ridiculed by Dr Mills using the simple comparison of energy in and out.
I'm sure you can tell where this is going so I will, to use a hunting metaphor, cut to the chase. Even 300 years ago, most people ate very little meat. It simply wasn't in great supply, and such as there was ended up on the plates of the kings and aristocracy. So it was the kings and aristocracy who looked like Henry VIII and keeled over aged 45 after a lifetime of gout. The rank and file had shorter lifespans than we do now, but that's largely down to high infant mortality and deaths from infectious diseases and accidents.
When the Industrial Revolution kicked in, meat (and dairy) was soon much more readily available. Our brains, the same brains that lit up like pinball machines when tasting that calorie dense, fatty meat on the savannah, still lit up in exactly the same way. We wanted more, and we could have more. More and more and more. On top of that, we worked out how to add even more of these chemicals to our food, the ones that really hit the spot. Sugar and fat, with salt for taste. Evolution simply hasn't had time to catch up. The same foods that, in small amounts, helped us survive to 30 are, in large amounts, killing us by 60.
Next time I'll be looking at The V Word - why following this diet may or may not make you vegan, and who cares?
[1] Yes, grandparents who survived long enough to help with child care or pass on learned knowledge would help humanoid species to survive, but it's very much a secondary effect compared to the drive to reproduce.
[2] Lions and hyenas can eat up to 30% of body weight at one sitting, the equivalent of me necking 200 quarter-pound burgers.
Further Viewing :
Milton Mills, MD - Are Humans Designed To Eat Meat?
Alan Goldhamer - Escaping the Dietary Pleasure Trap
A couple of technical points.
ReplyDelete1) I think that meat-eating continued to exist beyond the era of hunter-gatherers because, in a world of refrigeration, an animal was "food on the hoof". It could often eat stuff indigestible to humans. Similarly, for stable "farming" communities there were certain efficiencies in keeping animals to eat, not least the spreading of risk (if a disaster caused your crops either to fail or to be lost after harvesting, your animals might see you through).
2) Meat and dairy were actually available in Europe far more widely (to ordinary people) in the 15th century. It became gradually more expensive (relatively) for the following 300 years. England survived this price-shift (basically a Malthusian event) better than much of western Europe. Even the Industrial Revolution didn't bring meat back down to the affordability of the early 15th century.
A look at the diets of "ordinary" western Europeans in the 15th and 16th centuries is really quite a surprise. Many small villages had more than one butcher's. I think that the existence of several "types" of butcher in France could be a function of the fact that much meat was available at a cheap price. "The "Fish on Friday" thing and other "sacrifices" were, I think, introduced as a response to meat becoming less affordable.