42
" We didn’t evolve to be healthy, but instead we were selected to have as many offspring as possible under diverse, challenging conditions. As a consequence, we never evolved to make rational choices about what to eat or how to exercise in conditions of abundance and comfort. What’s more, interactions between the bodies we inherited, the environments we create, and the decisions we sometimes make have set in motion an insidious feedback loop. We get sick from chronic diseases by doing what we evolved to do but under conditions for which our bodies are poorly adapted, and we then pass on those same conditions to our children, who also then get sick. If we wish to halt this vicious circle then we need to figure out how to respectfully and sensibly nudge, push, and sometimes oblige ourselves to eat foods that promote health and to be more physically active. That, "
― Daniel E. Lieberman , The Story of the Human Body: Evolution, Health, and Disease
43
" Remember, “Nothing in biology makes sense except in the light of evolution.” Our evolutionary history thus accounts for how and why our skeletons, hearts, intestines, and brains work the way they do. Evolution also explains how and why in the course of a mere 6 million years we changed from being apes in an African forest to being upright, striding bipeds who peer through telescopes into distant galaxies searching for other forms of life. It’s been an amazing 6 million years, but our species’ evolution occurred through just a few transformations. None of these shifts were drastic, all of them were chance events contingent on previous changes, and, more often than not, they were driven by climate change. In the grand scheme of things, if there is any one most transformative human adaptation that we evolved it must be our ability to evolve through culture rather than just natural selection. Today, cultural evolution is outpacing and sometimes outwitting natural selection. Many recent human inventions were adopted because they helped our ancestors produce more food, harness more energy, and have more children. Unintended by-products of these cultural innovations, however, were increased levels of infectious disease from larger, denser populations, inadequate sanitation, and less nutritious food. Civilization also brought extreme famines, dictatorships, war, slavery, and other modern misfortunes. In recent years we have made much progress to redress these man-made problems, and arguably people in the developed world are now better off than hunter-gatherers ever were. "
― Daniel E. Lieberman , The Story of the Human Body: Evolution, Health, and Disease
44
" More than six hundred generations ago, everybody everywhere was a hunter-gatherer. Until relatively recently—the blink of an eye in evolutionary time—your ancestors lived in small bands of fewer than fifty people. They moved regularly from one camp to the next, and they survived by foraging for plants as well as hunting and fishing. Even after agriculture was invented starting about 10,000 years ago, most farmers still lived in small villages, labored daily to produce enough food for themselves, and never imagined an existence now common in places like Tampa, Florida, where "
― Daniel E. Lieberman , The Story of the Human Body: Evolution, Health, and Disease
45
" Natural selection is a remarkably simple process that is essentially the outcome of three common phenomena. The first is variation: every organism differs from other members of its species. Your family, your neighbors, and other humans vary widely in weight, leg length, nose shape, personality, and so on. The second phenomenon is genetic heritability: some of the variations present in every population are inherited because parents pass their genes on to their offspring. Your height is much more heritable than your personality, and which language you speak has no genetically heritable basis at all. The third and final phenomenon is differential reproductive success: all organisms, including humans, differ in how many offspring they produce who, themselves, survive to reproduce. Often, differences in reproductive success seem small and inconsequential (my brother has one more child than I do), but these differences can be dramatic and significant when individuals have to struggle or compete to survive and reproduce. Every winter, about 30 to 40 percent of the squirrels in my neighborhood perish, as did similar proportions of humans during great famines and plagues. The Black Death wiped out at least a third of Europe’s population between 1348 and 1350. If you agree that variation, heritability, and differential reproductive success occur, then you must accept that natural selection occurs, because the inevitable outcome of these combined phenomena is natural selection. Like "
― Daniel E. Lieberman , The Story of the Human Body: Evolution, Health, and Disease
49
" Like it or not, we are slightly fat, furless, bipedal primates who crave sugar, salt, fat, and starch, but we are still adapted to eating a diverse diet of fibrous fruits and vegetables, nuts, seeds, tubers, and lean meat. We enjoy rest and relaxation, but our bodies are still those of endurance athletes evolved to walk many miles a day and often run, as well as dig, climb and carry. "
― Daniel E. Lieberman , The Story of the Human Body: Evolution, Health, and Disease
51
" A first question to ask before considering how farming affected the human body is why did farming develop in so many places and in such a short span of time after millions of years of hunting and gathering? There is no single answer to this question, but one factor might have been global climate change. The Ice Age ended 11,700 years ago, ushering in the Holocene epoch, which has not only been warmer than the Ice Age, but also more stable, with fewer extreme fluctuations in temperature and rainfall.2 During the Ice Age, hunter-gatherers sometimes attempted to cultivate plants through trial and error, but their experiments didn’t take root, perhaps "
― Daniel E. Lieberman , The Story of the Human Body: Evolution, Health, and Disease
57
" Hunter-gatherers tend to be highly migratory, but incipient farmers benefit from settling down into permanent villages to tend and defend their crops, fields, and herds year-round. Pioneer farmers also domesticated certain plant species by selecting—either consciously or unconsciously—plants that were larger and more nutritious as well as easier to grow, harvest, and process. Within generations, such selection transformed the plants, making them dependent on humans to reproduce. For "
― Daniel E. Lieberman , The Story of the Human Body: Evolution, Health, and Disease
58
" the Mediterranean region’s climate started to warm and become wetter starting 18,000 years ago, archaeological sites become more numerous and widespread, creeping into areas now occupied by the desert. The culmination of this population boom was a period called the Natufian, dated to between 14,700 and 11,600 years ago.7 The early Natufian was a sort of golden era of hunting and gathering. Thanks to a benevolent climate and many natural resources, the Natufians were fabulously wealthy by the standards of most hunter-gatherers. They lived by harvesting the abundant wild cereals that naturally grow in this region, and they also hunted animals, especially gazelle. The Natufians evidently had so much to eat that they were able to settle permanently in large villages, with as many as 100 to 150 people, building small houses with stone foundations. They also made beautiful art objects, such as bead necklaces and bracelets and carved figurines, they exchanged with distant groups for exotic shells, and they buried their dead in elaborate graves. If there ever was a Garden of Eden for hunter-gatherers, this must have been it. But then crisis struck 12,800 years ago. All of a sudden, the world’s climate deteriorated abruptly, perhaps because an enormous glacial lake in North America emptied suddenly into the Atlantic, temporarily disrupting the Gulf Stream and wreaking havoc with global weather patterns.8 This event, called the Younger Dryas,9 effectively plunged the world back into Ice Age conditions for hundreds of years. Imagine "
― Daniel E. Lieberman , The Story of the Human Body: Evolution, Health, and Disease
60
" In short, the combined effects of lower infant mortality, higher longevity, and increased fertility have fueled an explosion in the world’s population, as figure 18 graphs. Since population growth is intrinsically exponential, even small increases in fertility or decreases in mortality spark rapid population growth. If an initial population of 1 million people grows at 3.5 percent per year, then it will roughly double every generation, growing to 2 million in twenty years, 4 million in forty years, and so on, reaching 32 million in a hundred years. In actual fact, the global growth rate peaked in 1963 at 2.2 percent per year and has since declined to about 1.1 percent per year,60 which translates into a doubling rate of every sixty-four years. In the fifty years between 1960 and 2010, the world’s population more than doubled, from 3 to 6.9 billion people. At current rates of growth, we can expect 14 billion people at the end of this century. FIGURE 21. The demographic transition model. Following economic development, death rates tend to fall before birth rates decrease, resulting in an initial population boom that eventually levels off. This controversial model, however, only applies to some countries. One major by-product of population growth plus the concentration of wealth in cities has been a shift to more urbanization. In 1800, only 25 million people lived in cities, about 3 percent of the world’s population. In 2010, about 3.3 billion people, half the world’s population, are city dwellers. "
― Daniel E. Lieberman , The Story of the Human Body: Evolution, Health, and Disease
