101
" Let’s first consider how farming led to natural selection. It bears repeating that the very first farmers lived about 600 to 500 generations ago, and in most parts of the world, farming has been practiced for less than 300 generations. From an evolutionary perspective, this is not much time for lots of major evolutionary change, such as a new species evolving, but it is enough time for genes with strong effects on survival and reproduction to change their frequencies appreciably within populations. In fact, because farming so profoundly altered people’s diets, the pathogens they encountered, the work they did, and the number of children they could have, the origins of agriculture probably intensified selection on certain genes. "
― Daniel E. Lieberman , The Story of the Human Body: Evolution, Health, and Disease
104
" Evolved to Run Walking long distances is fundamental to being a hunter-gatherer, but people sometimes have to run. One powerful motivation is to sprint to a tree or some other refuge when being chased by a predator. Although you only have to run faster than the next fellow when a lion chases you, bipedal humans are comparatively slow. The world’s fastest humans can run at 37 kilometers (23 miles) per hour for about ten to twenty seconds, whereas an average lion can run at least twice as fast for approximately four minutes. Like us, early Homo must have been pathetic sprinters whose terrified dashes were too often ineffective. However, there is plentiful evidence that by the time of H. erectus our ancestors had evolved exceptional abilities to run long distances at moderate speeds in hot conditions. The adaptations underlying these abilities helped transform the human body in crucial ways and explain why humans, even amateur athletes, are among the best long-distance runners in the mammalian world. Today, humans run long distances to stay fit, commute, or just have fun, but the struggle to get meat underlies the origins of endurance running. To appreciate this inference, try to imagine what it was like for the first humans to hunt or scavenge 2 million years ago. Most carnivores kill using a combination of speed and strength. Large predators, such as lions and leopards, either chase or pounce on their prey and then dispatch it with lethal force. These dangerous carnivores can run as fast as 70 kilometers (43 miles) per hour, and they have terrifying natural weapons: daggerlike fangs, razor-sharp claws, and heavy paws to help them maim and kill. Hunters "
― Daniel E. Lieberman , The Story of the Human Body: Evolution, Health, and Disease
105
" argued that the solution to this problem is an ancient method of hunting based on endurance running known as persistence hunting.36 Persistence hunting takes advantage of two basic characteristics of human running. First, humans can run long distances at speeds that require quadrupeds to switch from a trot to a gallop. Second, running humans cool by sweating, but four-legged animals cool by panting, which they cannot do while galloping.37 Therefore, even though zebras and wildebeest can gallop much faster than any sprinting human, we can hunt and kill these swifter creatures by forcing them to gallop in the heat for a long period of time, eventually causing them to overheat and collapse. This is just what persistence hunters do. Typically, "
― Daniel E. Lieberman , The Story of the Human Body: Evolution, Health, and Disease
106
" the case of arteries, oxidization of LDLs causes an inflammation in the cells that make up the arterial wall, which then triggers white blood cells to come and clean up the mess. Unfortunately, the white blood cells trigger a positive feedback loop because part of their response is to create a foam that traps more small LDLs, which then also get oxidized. Eventually, this foamy mixture coagulates into a stiffened accumulation of crud on the artery wall, known as a plaque. Your body fights plaques primarily with HDLs, which scavenge cholesterol from the plaque and return it to the liver. Plaques thus develop not just when LDL levels (again, mostly the small ones) are high but also when HDL levels are low. If "
― Daniel E. Lieberman , The Story of the Human Body: Evolution, Health, and Disease
115
" Looking more closely, there are two pathways that link energy and estrogen to higher rates of reproductive cancers among women in developed countries. The first is how many menstrual cycles women experience. The average woman in countries such as the United States, England, and Japan starts menstruating when she is twelve or thirteen years old, and she continues to menstruate until her early fifties. Because she has access to birth control, she gets pregnant only once or twice over her lifetime. Further, after she gives birth, she probably breast-feeds her babies for less than a year. All told, she can expect to experience approximately 350 to 400 menstrual cycles during her life. In contrast, a typical hunter-gatherer woman starts menstruating when she is sixteen, and she spends the majority of her adult life either pregnant or nursing, often struggling to get enough energy to do so. She thus experiences a total of only about 150 menstrual cycles. Since each cycle floods a woman’s body with powerful hormones, it is not surprising that reproductive cancer rates have multiplied in recent generations as birth control and affluence has spread. The other key pathway that links chronic positive energy balances with reproductive cancers among women is through fat. Earlier, "
― Daniel E. Lieberman , The Story of the Human Body: Evolution, Health, and Disease
118
" In short, an evolutionary perspective explains why the embarrassment of riches many people now enjoy elevates their levels of reproductive hormones, which, along with birth control, then increases the likelihood that cancers will evolve in their breasts, ovaries, uteruses, and prostates. Many reproductive cancers are thus mismatch diseases that are ultimately linked to having lots of energy to spare. As economic development and processed food diets sweep "
― Daniel E. Lieberman , The Story of the Human Body: Evolution, Health, and Disease
119
" Many of the traits benefit both walking and running, but some, such as a large gluteus maximus, the nuchal ligament, big semicircular canals, and short toes don’t affect how well we walk and are primarily useful when we run, which means they are adaptations to running. These traits suggest that there was strong selection in the genus Homo not just for walking but also for running, presumably for scavenging and hunting. Consider also that a few of these adaptations, especially long legs and short toes, compromise our ability to climb trees. Selection for running may have caused the human genus to become the first primates that are clumsy in trees. In short, the benefits of acquiring meat through scavenging and hunting account for many transformations of the human body first evident in early Homo that enabled early hunter-gatherers not only to walk but also to run long distances. Whether "
― Daniel E. Lieberman , The Story of the Human Body: Evolution, Health, and Disease
