字幕表 動画を再生する 英語字幕をプリント Thank you, it's a pleasure to be here. I'm an archaeological scientist and I study the health and dietary histories of ancient peoples using bone biochemistry and ancient DNA. I'm here because I want to talk to you about the Paleo Diet. It's one of America's fastest growing diet fads. The main idea behind it is that the key to longevity and optimal health is to abandon our modern agricultural diets, which make us ill, and move far back in time to our Palaeolithic ancestors, more than 10,000 years ago, and eat like them. Now, I'm really interested in this idea because it purports to put archaeology in action, to take information we know about the past and use it in the present to help us today. Now, this idea was really started in the 1970s with this book, "The Stone Age Diet." It's diversified since then into several variants, including the Paleo Diet, the Primal Blueprint, the New Evolution Diet, and Neanderthin, and most of the language of these diets makes references to anthropology, nutrition science, and evolutionary medicine. The diet does seem primarily targeted at men, so if you look at advertisements and descriptions, they have virile, cavemen-like images, things like "live primal," lots of red meat. And basically, the idea behind it can be broken down into four parts. One is that our agricultural diets today make us chronically ill, that they are out of sync with our biology. And two, that we need to abandon these agricultural diets that started during the agricultural period, and move back in time to the Palaeolithic and eat more like our ancestors over 10,000 years ago. Third, that we know what these diets were like, and what they were like was they had a lot of meat, they were mainly meat based. That was supplemented with vegetables and fruits and some nuts and oils, but it definitely did not contain grains or legumes or dairy. And fourth, that if we emulate this ancient diet, it will improve our health and make us live longer. So what I want to talk to you about today is that this version of the Paleo Diet that's promoted in popular books, on TV, on self-help websites and in the overwhelming majority of press has no basis in archaeological reality. So, thank you! (Laughter) No, I'm not going to end there; I will explain. So what I want to do as an archaeologist is go through this, do a bit of myth-busting of some of these foundational archaeological concepts upon which it's based, and then I want to talk to you about what we really do know from the archaeological record and from scientific studies about what Palaeolithic people did eat. So, myth one is that humans are evolved to eat meat and that Palaeolithic peoples consumed large quantities of meat. Humans have no known anatomical, physiological, or genetic adaptations to meat consumption. Quite the opposite, we have many adaptations to plant consumption. Take, for example, vitamin C. Carnivores can make their own vitamin C, because vitamin C is found in plants. If you don't eat plants, you need to make it yourself. We can't make it, we have to consume it from plants. We have a longer digestive tract than carnivores. That's because our food needs to stay in our bodies longer, so we have more time to digest plant matter. We need more surface area, we need more microbes. We have generalist dentition, so we have big molars that are there to shred fibrous plant tissue. We do not have carnassials, which are the specialised teeth that carnivores have to shred meat, and we do actually have some genetic mutations in some populations that are adaptive to animal consumption, but it's to milk, not meat, and these arose in certain populations during agricultural periods primarily in Europe and Africa. I call this "The Meat Myth." The idea behind it is that we should eat all this red meat, but that's just really not true. The meats on this plate of meat here are from fattened cattle, these are domestic animals. Anything a Palaeolithic person would have eaten would have probably been very lean, probably small, and they wouldn't really have eaten that much meat. Of course there's also bone marrow and organs, these would have been very important. We see evidence of harvesting of bone marrow in faunal assembles where you see characteristic cutting open of the bones, like you see here, for marrow extraction. Now sure, people did eat meat, and especially in the Arctic and areas with long periods where plants were not available, they would have eaten a lot of meat. But people that lived in more temperate or tropical regions would have had a very large plant portion of their diet. So where does this Meat Myth come from? There's really two places, and one is the inherent bias in the archaeological record. Bone is 80% mineral by weight, it's going to preserve better and longer over thousands of years than delicate plant remains. But the other issue comes from some early bone biochemistry studies that were performed on Neanderthals and early people. This bone biochemistry study is based on something called nitrogen stable isotope analysis. It's complicated, but I'm going to try and break it down. The basic idea is that you are what you eat, and so we - there's nitrogen-15 and nitrogen-14, heavy and light versions of nitrogen - and we consume this nitrogen in our food. But there's one important difference, and that is, with each step that you go up the trophic hierarchy, the amount of the heavier isotope increases. So if you measure the amount of heavy isotope in the bone, you can infer where that individual was on a food chain. This is an example of a generalized isotopic model. I've plotted where plants generally fall, and above them are the herbivores, and then above them, the carnivores. But one of the problems is that not all ecosystems conform to this model. There's a lot of regional variability, so if you don't understand the region, you can come to erroneous conclusions. I'll give you some examples: we can take East Africa; if we measure animals and ancient humans, in East Africa, we see some very strange patterns. First of all, how can a human be higher than a lion? Lions only eat other animals. And then, how is this herbivore above a lion? Well, it turns out that the food that you eat is not is not the only contributor to these isotopic values. and that aridity can also have an impact. So what we're likely seeing here is differences in water access. So let's move out of the savannah and move into the tropical areas. Let's look at the ancient Maya; again we see something anomalous. We see the ancient Maya lining up with jaguars. Now, we know the ancient Maya had a diet heavily reliant on corn. So what's happening here? We don't exactly know, but we think this may have to do with the way they performed agriculture and how they fertilised their crops. Now let's go to the Pleistocene. We see some really interesting patterns here too. We see reindeer plotting very low, in the range of plants. We see wolves plotting normally where you would see herbivores, and we see mammoths spanning all three levels, at once plants, herbivores and carnivores. So what we think is happening here is that in very cold climates, animals eat unusual things. and in this case what we think is happening is these mammoths are eating lichens and bark and that's giving them very strange values. So if we now go to humans, ancient humans, Palaeolithic humans, and Neanderthals, we see that they plot in the same isotopic space as wolves and hyenas. Now that's true, but as I've shown, if you don't have good control over the regional isotopic ecology, you can come to an erroneous conclusion, and I think it's premature to say this is very strong evidence of meat consumption, given how very little we really know about the Palaeolithic ecosystems. So, myth two is that Palaeolithic peoples did not eat whole grains or legumes. Now, we have stone tool evidence from at least 30,000 years ago - that's 20,000 years before the invention of agriculture - of people using stone tools that look like mortars and pestles to grind up seeds and grain. More recently we've been developing techniques where we can actually measure this thing called "dental calculus." It's very interesting: it's fossilized dental plaque. We can go in the individual mouths of people, pull out that plaque and recover microfossils of plants and other remains. My team is working on developing methods to extract DNA and proteins, and other research groups are focussing on these microfossils like starch grains, pollen and phytoliths. Now, we're still in early days here, but even with the limited research we have, we can say that there is an abundance of plant remains inside the dental calculus of Paleolithic peoples. And these things include grains, including barley. We're finding barley inside Neanderthal teeth, or inside the plaque. We also have legumes and tubers. So, myth three is that Paleo Diet foods, in the fad diet, are what our Palaeolithic ancestors ate.