In this video, I'm going to introduce the concept of ancient instincts and give you some examples that do not involve water or sanitation. In the next video, I will move to water and sanitation related ancient instincts. I'll be the first to admit that my narrative is speculative. Evolutionary biologists estimate that a group of perhaps 100 to 150 individuals left east Africa about 60,000 years ago. Almost everyone alive today is a descendant of that small group. That is only about 3,000 generations ago, so we really are all one human family. As I read the literature, this out of Africa hypothesis has strong support based on the genetic evidence. Our ancestors left Africa with language and clothing and a simple tool kit. In addition, our ancestors left Africa with bodies built for running. Members of our species are great endurance runners. Anthropologists have speculated that we became long distance runners to chase down large mammals. My own brother is one of these crazy long distance runners. So this is surely part of my own genetic makeup. I believe that we also left with a set of ancient instincts. These are shared with human beings today. I'm not an evolutionary biologist or a psychologist so I'm not going to try to precisely define this concept of ancient instincts, but let me begin by describing some of their attributes. First, ancient instincts must have conferred an evolutionary advantage on humans for a very long time. Second, some influence our preferences and behavior subconsciously. Others we are conscious of but they still exert a powerful influence on our preferences and behavior. Third, in some cases it's possible to overcome the influences of ancient instincts. But for some people it is very hard to make behavioral changes that move against these influences. Fourth, it seems possible that some ancient instincts are malleable and can change. But sometimes this change may be very difficult and slow. To make this concept more concrete, let me give you four examples of what I mean by ancient instincts. The first of these ancient instincts is our fear of snakes. Lynne Isbell has argued the primate's ability to see colors and detect patterns has evolved in an arms race with snakes. She calls this snake detection theory. Interestingly for chimpanzees, this instinctual fear of snakes has to be triggered in infants. If a rubber snake is placed in a cage with baby chimpanzees and there are no adults, the baby chimpanzees are not afraid of the snake. But if the adults come into the cage and see the snake, there's screams of alarm about the snake trigger and instinctual response in the baby chimpanzees who instantly seem to understand that snakes pose a danger. I'm not making this stuff up. There's a series of scientific articles and serious journals on chimps, phobias and snakes. This concept of triggering is interesting and seems to apply to at least some other ancient instincts as well. This concept of triggering is different than learning. The baby chimpanzees do not need to be trained to think rationally about the risks snakes pose. We're not talking about an education intervention here. But an intervention is needed to start the triggering and the trigger is hearing an emotional response from the mother. The second ancient extinct that we all seem to share is a love of a particular kind of landscape. We all find landscape with some large trees, water and open grass land or pasture aesthetically pleasing. You see this ancient instinct mirrored here in this landscape of an English estate. The key elements, again, are water, pasture and large trees. Jay Appleton, a British geographer at the University of Hull, has proposed a theory to explain our response to different habitats. It's called prospect refuge theory. His book, The Experience of Landscape, was published in 1975. Water is a central feature in prospect refuge theory. We want a landscape that offers good prospects for food and water and a place to sleep as a refuge from danger. Land near water sources providing a good prospect for game, a refuge in times of scarcity, and water for relaxation and recreation. Interestingly, the geographers refer to innate mechanisms that influence our response to environmental habitats. Innate mechanisms seems to me very close to my understanding of ancient instincts. A closely related idea to prospect refuge theory is the savannah hypothesis, first proposed by Gordon Orians at the University of Washington. The savannah hypothesis argues that evolution shaped our love of a particular landscape. There were trees for sleeping, grasslands for game and water for drinking and relaxation. Orians did a series of experiments. He showed small children from all over the world different landscapes and they almost always picked the savannah landscape as the one they preferred. The savannah hypothesis also closely related to E.O. Wilson's Biophilia Hypothesis that people feel happy when they are in nature and surrounded by plants and animals. Again, this ancient instinct is most readily seen in children. Children love to go to zoos. A third ancient instinct is our love of sugar. Sugar gives us a quick energy boost and access to sugar would have had an evolutionary advantage. But for most of human history, sugar was hard to find. There is archaeological evidence that our love of sugar is very old. On the right is a cave drawing showing a hunter-gatherer collecting honey from a beehive. But how did he find the hive? He might have had help from the bird on the left, a greater honeyguide adult. The greater honeyguide and hunter-gatherers evolved in evolutionary bargain. The honeyguide finds the hive and then leads the hunter-gatherer to it, both issuing a series of calls. Then the hunter-gatherer breaks open the hive, which the honeyguide cannot do. And the hunter-gatherer and the honeyguide share the honey. Of course, the human takes most of the honey, not the bird. Our ancestors craved sugar and we still do. As an aside, interestingly, our taste buds are different for sugar and hunger and for thirst. Let's identify one more ancient instinct. How do you feel when a shadow passes overhead? Do you duck and cover your head? Do you feel a tingling on the back of your neck and look up quickly? What is the origin of this reaction? In 1924 a fossil was found in South Africa on the edge of the Kalahari Desert during a mining excavation. It was perhaps the most important hominid fossil ever found. It was an almost complete Australopithecus skull. It was child's skull about 2 million years old. The Taung child had a brain about the size of a chimpanzee, but walked upright. It was found in a cave with piles of other bones. These fossils were all boxed up and by chance sent to a South African neuroanthropologist named Raymond Dart, who immediately recognized the importance of this skull. He quickly published a paper in the journal, Nature, in 1925 describing the skull. This is a replica of the Taung child's skull. It's true to size. Here's a picture of Raymond Dart with the skull of the Taung child in the pages of Nature in 1925. Dart's assertion of the importance of the Taung child was largely dismissed by scientists in the 1920s and 30s because at the time it seemed impossible to Europeans that humans could have originated from Africa. It was the work of Louis and Mary Leakey in Ethiopia decades later that reasserted the claim of the African origins of our ancestors and laid out the foundations for the out of Africa hypothesis. After the Leakey's discoveries there was renewed interest in the Taung child's skull and the question of how the Taung child died. Dart thought that the child was killed by other hominids. Conventional wisdom in the latter part of the 20th century coalesced around a big cat like a lion or leopard. But in 2006, Lee Berger, a university researcher in South Africa, wrote this paper that proved that the Taung child was killed by a large raptor, probably an eagle. He found pinhole marks from the raptor's talons in the original Taung child's skull. And most tellingly, scratches in the sockets where the eagle dug out the eyes. The arrows in the slide are pointing toward the scratches in the eye sockets of the skull in the photo. This replica was made with a 3D printer, and you can't actually see the scratches, but you can in the original. So the answer to the question about why we react to shadows is that we have an ancient instinct inherited from our ancestors to watch for and react to danger from above, raptors. These are four examples of ancient instincts that we still carry with us today. I'm sure there are others. Is our love of dogs an ancient instinct? Many people care deeply about their dogs. I grew up with dogs and my parents own dogs and all my siblings have dogs. So I understand how passionately some people care about dogs but not everyone does. Our love of dogs is not that ancient. Our ancestors went through a genetic bottleneck about 20,000 years ago and most of them emerged from Central Asia. Dogs were only domesticated from wolves about 15,000 years ago, so it's not surprising that some of us do not feel as passionately about dogs as we do about snakes or sugar. Or as passionately as the woman in this picture. Some people sleep with dogs in their beds, but others are repulsed by the idea. For me, the love of dogs doesn't qualify as an ancient instinct because it is too new and not universal. Some of our ancient instincts still serve a useful purpose. For example, fear of snakes still serves an evolutionary purpose in many locations. In most cities, it is no longer useful but it does not cause us any great problem. And even urban residents may venture out into the wilderness occasionally, and an ancient fear of snakes may prove helpful. For the last ten years, I've had the privilege of working in Costa Rica for the Latin America and Caribbean Environmental Economics Program based in CATIE and Turrialba, Costa Rica. My wife and I make one or two trips a year and I look forward every year to going. But this is the snake I don't want to step on, the fer-de-lance, also known as the ultimate pit viper. It can be two meters long and hard to see. Recall Lynne Isbel's arms race. As they still pose a danger to me, I'm happy to have retained my ancient instinct to fear snakes. But other ancient instincts no longer serve an evolutionary purpose. Our love of sugar and inability to control our eating has led to an epidemic of obesity in many parts of the world, even among children. In summary, ancient instincts are hard to define but we tend to know one when we see it. In the next video, I will focus on ancient instincts that involve water and sanitation. But before you watch the next video, I'd like you to watch a short video simply entitled Water Holes.