The Story of the Human Body

why do we as modern day humans do harmful things?

I think there are other, deeper evolutionary explanations for why humans sometimes do novel things that are potentially harmful. Chief among them is that we don't actually consider many novel behaviors to be potentially harmful because we don't consider them novel and we are psychologically disposed to consider the world around us to be normal, hence benign. • we humans (myself included) sometimes behave in ways that are not in our best interests because we lack sufficient information, we cannot control our environments, we are unfairly manipulated by others, and— crucially— because we are poorly adapted to control deep cravings for comforts and calories that used to be rare.

What was the 4th evolutionary transition?

As archaic human hunter-gatherers flourished and spread across much of the Old World, they evolved even bigger brains and larger, more slowly growing bodies. To be sure, the first hunter-gatherers 2 million years ago were not as cognitively advanced as people today, but they must have benefited from having bigger, better brains than australopiths. Then, once hunting and gathering became successful enough to make more energy available, this way of life permitted selection for the evolution of yet larger brains. It is not coincidental that major increases in brain size occurred after the origins of hunting and gathering. By 600,000 years ago, some of the descendants of H. erectus had evolved sufficiently from their ancestors to merit being classified in different species. The best known is Homo heidelbergensis, also shown in figure 11, which extended from southern Africa to England and Germany. However, around 500,000 years ago archaic Homo invented a new and ingenious method of fabricating very thin stone tools with predetermined shapes, including triangular points. This method takes great skill and much practice to master, but it revolutionized projectile technology because stone points made in this fashion are light and sharp enough to haft onto spears using pitch or sinew. Imagine what a difference these stone points made to hunters! Spears suddenly became much sharper: instead of bouncing off their prey, they could penetrate tough animal hides and even ribs, and once lodged inside, their jagged edges inflicted horrible, lacerating wounds. Armed with thin stone points, hunters could now kill prey from greater distances, decreasing a hunter's chances of getting injured while increasing the chances of success. Other tools made from this prepared-core technique were also better for skinning hides and performing other tasks.

What is one of the most important lessons to learn from our evolutionary history?

If there is any one most useful lesson to learn from our species' rich and complex evolutionary history, it is that culture does not allow us to transcend our biology. Human evolution never was a triumph of brains over brawn, and we should be skeptical of the science fiction that the future will be any different. Clever as we are, we cannot alter the bodies we inherited in more than superficial ways, and it is dangerously arrogant to think we can engineer feet, liver cells, brains, or other body parts any better than nature already does. 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.

Why do we sleep differently than we used to?

Many factors account for how and why we sleep so differently than we used to: 1) is that the Industrial Revolution transformed time and provided us with bright lights, radio, television shows, and other fun things to entertain and stimulate us well beyond an evolutionarily normal bedtime hour. 2) For the first time in millions of years, much of the world can now stay up late, encouraging sleep deprivation. 3) On top of that, many people today suffer from insomnia because they experience more stress from some mix of physical and psychological factors, such as too much alcohol, poor diet, lack of exercise, anxiety, depression, and various worries. It is also possible that the unusual, stimulus-free environments in which we now like to sleep further promote insomnia. Falling asleep is a gradual process in which the body goes through several stages of light sleep and the brain becomes progressively less aware of outside stimuli before entering a deep stage of sleep in which one is unaware of the outside world. Perhaps insomnia sometimes occurs because by isolating ourselves in insulated bedrooms we don't hear evolutionarily normal sounds such as the hearth crackling, people snoring, and hyenas barking far in the distance, reassuring subconscious parts of the brain that everything is okay.

What was the 5th evolutionary transition?

TRANSITION FIVE: Modern humans evolved special capacities for language, culture, and cooperation that allowed us to disperse rapidly across the globe and to become the sole surviving species of human on the planet. using multiple lines of evidence that we can state with a reasonable degree of confidence that modern humans evolved from archaic humans in Africa at least 200,000 years ago. Our recent divergence from a small population explains another important fact, one that every human ought to know: we are a genetically homogenous species. If you catalog all the genetic variations that exist throughout our species, you'd find that approximately 86 percent are found within any one population. To put this fact into perspective, you could wipe out the entire population of the world except for, say, Fiji or Lithuania and still retain almost every human genetic variation. Then, starting about 50,000 years ago, something extraordinary happened: Upper Paleolithic culture was invented. The exact time and place of this revolution is murky, but it may have begun in northern Africa and then spread rapidly northward into Eurasia and southward into the rest of Africa. One very obvious difference about the Upper Paleolithic was how people produced stone tools. In the Middle Paleolithic, complex tools were made in a very laborious and technically demanding way, but Upper Paleolithic toolmakers figured out how to mass manufacture long, thin blades of stone from the edges of prism-shaped cores. Another component of the Upper Paleolithic revolution is cultural change. Almost nothing ever changed in the Middle Paleolithic: sites from France, Israel, and Ethiopia are all basically the same regardless of whether they are 200,000, 100,000, or 60,000 years old. But as soon as the Upper Paleolithic begins around 50,000 years ago, one can use artifacts to identify distinctive cultures that have discrete distributions in time and space. In short, if there is anything most different about modern humans compared to our archaic cousins it is our remarkable capacity and proclivity to innovate through culture.

What was the first evolutionary transition?

TRANSITION ONE: The very earliest human ancestors diverged from the apes and evolved to be upright bipeds. regularly standing and walking upright was initially selected to help the first hominins forage and obtain food more effectively in the face of major climate change that was occurring when the human and chimpanzee lineages As we have seen, the first bipeds didn't get up on two feet in order to free their hands; instead they probably became upright in order to forage more efficiently and to reduce the cost of walking (if the LCA was a knuckle walker).

What was the 3rd evolutionary transition?

TRANSITION THREE: About 2 million years ago, the earliest members of the human genus evolved nearly (though not completely) modern human bodies and slightly bigger brains that enabled them to become the first hunter-gatherers. Our bodies and the way we behave evolved to be much more recognizably "human" at the dawn of the Ice Age, a truly pivotal period of change in the earth's climate that was initiated by continued global cooling between 3 and 2 million years ago. According to the best evidence currently available, H. erectus first evolved in Africa by 1.9 million years ago and then rapidly started to disperse from Africa into the rest of the Old World. H. erectus (or a closely related species) shows up in the Caucasus Mountains of Georgia by 1.8 million years ago and in both Indonesia and China by 1.6 million years ago. the evolution of humanlike bodies happened in at least two stages. First, in H. habilis, the brain expanded slightly and the face lost its snout. Then, in H. erectus, much more modern-shaped legs, feet, and arms evolved along with smaller teeth and modestly bigger brains. To be sure, H. erectus's body was not 100 percent like yours, but the evolution of this key species marks the origin of a largely humanlike body, as well as the modern ways we eat, cooperate, communicate, use tools, and otherwise behave. In essence, H. erectus was the first ancestor we can characterize as significantly human. Hunter-gatherers have been scavenging for millions of years, but there is archaeological evidence that by 1.9 million years ago early humans were hunting large animals like wildebeest and kudu. 34 If running was important for scavenging, imagine how important running was for the first hunters, who were slow and poorly armed.

What was the 2nd evolutionary transition?

TRANSITION TWO: The descendants of these first ancestors, the australopiths, evolved adaptations to forage for and eat a wide range of foods other than mostly fruit. The australopiths lived in Africa between about 4 and 1 million years ago, and we know much about them thanks to a rich fossil record of their remains. There are two good reasons to pay attention to the australopiths. 1. the genus Homo would not have evolved if Australopithecus had not become less arboreal, more habitually bipedal, and less dependent on fruit, setting the stage for subsequent evolution occasioned by yet more climate change. 2. Even more important, there is a lot of australopith in all of us. Humans are odd apes because we spend little to no time in trees (were you arboreal today?), we walk a lot, and we don't eat just fruit for breakfast, dinner, and lunch. These trends might have begun when we initially split from the apes, but they intensified remarkably over the millions of years during which various species of australopiths evolved. Nevertheless, you are not an australopith. Compared to Lucy and her kin, your brain is three times bigger, and you have long legs, short arms, and no snout. Instead of eating lots of low-quality food, you rely on very high quality food like meat, as well as tools, cooking, language, and culture. These and many other important differences evolved during the Ice Age, which began around two and a half million years ago.

What were Neanderthals like?

The most important facts about Neanderthals are that they were a species of archaic Homo that lived in Europe and western Asia between about 200,000 and 30,000 years ago. They were skilled and intelligent hunters, well adapted by natural selection and well supported by their wits to survive the cold, semi-arctic conditions of the Ice Age. However, they were bigger-brained, with average brain volumes of nearly 1,500 cubic centimeters. The Neanderthals were successful and talented hunter-gatherers who would probably still exist had it not been for H. sapiens. The Neanderthals made complex and sophisticated stone tools that they fashioned into a wide variety of tool types such as scrapers and points. They cooked their food and hunted big animals like wild aurochs, deer, and horses. But the Neanderthals, in spite of their accomplishments, were not entirely modern in their behavior. They made few tools out of bone, including needles, even though they must have made clothes from pelts. They buried their dead simply, and they left almost no traces of symbolic behavior such as art. They rarely ate fish or shellfish, even though these were abundant in some of the habitats in which Neanderthals lived. They seldom transported raw materials more than 25 kilometers (15.5 miles). As we will see, when modern humans did arrive in Europe starting about 40,000 years ago, they mostly replaced the Neanderthals. My guess is that Neanderthals were extremely smart, but that modern humans are more creative and communicative. Although archaic humans such as the Neanderthals surely had language, the uniquely short and retracted face of modern humans would have made us better at uttering clear, easy-to-interpret speech sounds at a very rapid rate.

Describe the theory of persistence hunting?

Typically, a hunter or a group of hunters will single out a large mammal (often the biggest possible) to chase in the middle of the day when it's hot. At the beginning of the chase, the animal gallops away to find a shady place to hide and cool by panting. But the hunters quickly follow by tracking, often at a walk, and then chase their prey again at a run, making the frightened creature gallop before it has had time to cool completely. Eventually, after many cycles of intermittent tracking and chasing— a combination of walking and running— the animal's body temperature rises to lethal levels, causing it to collapse from heatstroke. At this point, a hunter can dispatch the animal safely, easily, and without sophisticated weapons. 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 an H. erectus could outrun a human today is impossible to know, but there is no doubt these ancestors left a legacy of adaptations throughout our bodies that explain how and why humans are one of the few mammals that can and do run long distances with ease, and why we are the only mammal that can run marathons in the heat. Further, cooperation among hunter-gatherers occurs not just among kin but also among unrelated members of the same group. Everyone helps everybody. Mothers help one another forage, process food, and take care of one another's children. Fathers help one another hunt, share the spoils of their successes, and work together to build shelters, defend resources, and more. These and other forms of cooperation, however, require complex cognitive skills beyond those of apes. To cooperate effectively one needs a good theory of mind (to intuit what another person is thinking), the ability to communicate through language, the faculty to reason, and an ability to suppress one's urges.

How did our hunter-gatherer ancestors live?

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.

Why was control of fire such an important invention>

§ No one is quite sure when humans first managed to regularly create and use fire. Currently, the earliest evidence for the controlled use of fire by humans comes from a million-year-old site in South Africa and from a 790,000-year-old site in Israel. 18 Traces of fire, however, remain rare until 400,000 years ago, when fireplaces and burnt bones start showing up regularly in sites, suggesting that archaic Homo, unlike H. erectus, habitually cooked its food. Cooking, when it did catch on, was a transformative advance. For one, cooked food yields much more energy than uncooked food and is less likely to make you sick. Fire also allowed archaic humans to keep warm in cold habitats, to fend off dangerous predators, like cave bears, and to stay up late at night.

What was the agricultural revolution?

• Starting around 12,000 years ago, a few groups of people began to settle down in permanent communities, grow plants, and domesticate animals. These shifts were probably gradual at first, but over the next few thousand years they sparked a worldwide agricultural revolution whose effects are still rocking the planet, as well as our bodies. ○ At first, growing food through casual cultivation was a supplemental activity that helped provision big families, but the combination of more offspring to feed plus benign environmental conditions increased the benefits of growing plants relative to the costs. Over generations, cultivated plants evolved into domesticated crops, and occasional gardens turned into farms. Food became more predictable. ○ 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 how profoundly stressful this shift was for the Natufians, who were living at high population densities in permanent villages but who still relied on hunting and gathering. Within a decade or less, their entire region became severely colder and drier, causing food supplies to dwindle. ○ Other Natufians, however, evidently dug in their heels and intensified their efforts to maintain their settled way of life. In this case, necessity appears to have been the mother of invention, because some of them experimented successfully with cultivation, creating the first agricultural economy somewhere in the area now encompassing Turkey, Syria, ○ the ancient town of Jericho (famous for its walls) had about fifty houses and supported a population of five hundred people. PPNA farmers also made elaborate ground stone tools for grinding and pounding food, created exquisite figurines, and plastered the heads of their dead. ○ And the change kept on coming. At first, PPNA farmers supplemented their diet by hunting, mostly for gazelle, but within a thousand years, they had domesticated sheep, goats, pigs, and cattle. ○ Soon thereafter, these farmers invented pottery. As these and other innovations continued to accrue, their new, Neolithic way of life flourished and expanded rapidly throughout the Middle East and into Europe, Asia, and Africa. It's almost certain you ate something today that these people first domesticated, and if your ancestors came from Europe or the Mediterranean, there's a good chance you have some of their genes. ○ Man's best friend, the dog, was actually the first domesticated species. We bred dogs from wolves more than 12,000 years ago, but there is much debate over when, where, and how this domestication occurred (and to what extent dogs actually domesticated us). ○ farming began, and was sometimes even higher, but there is no question that it launched the first major population explosion in human history. ○ According to some estimates, the world probably had more than a thousand different languages by the end of the Neolithic. ○ If farming was "the biggest mistake in human history," which triggered lots of evolutionary mismatch diseases, then why did it spread so rapidly and thoroughly? The biggest reason is that farmers pump out babies much faster than hunter-gatherers. In today's economy, a higher reproductive ○ In fact, a large part of the success of farming is that farmers breed their own labor force more effectively than hunter-gatherers, which pumps energy back into the system, driving up fertility rates. 20 Farming therefore leads to exponential population growth, causing farming to spread. ○ The very first farmers certainly had to work hard, but we know from archaeological sites that they still hunted animals, did some gathering, and initially practiced cultivation on a modest scale. Farming pioneers surely had challenging lives, but the popular image of the incessant drudgery, filth, and misery of being a farmer probably applies more to later peasants in feudal systems than to early Neolithic farmers. ○ One of the biggest problems is a loss of nutritional variety and quality. Hunter-gatherers survive because they eat just about anything and everything that is edible. Hunter-gatherers therefore necessarily consume an extremely diverse diet, typically including many dozens of plant species in any given season. ○ even though the Agricultural Revolution led to selection that helped struggling farmers cope with novel diets and infectious diseases, it would be wrong to conclude that natural selection has been the dominant engine of evolutionary change over the last few thousand years. By any yardstick, recent genetic adaptations that have evolved independently in different parts of the New and Old Worlds are modest compared to the scale and degree of cultural innovation that humans have cooked up over the same time frame. Many of these cultural innovations— the wheel, plows, tractors, writing— have improved economic productivity, but quite a few were responses to mismatch diseases caused by the farming way of life. ○ Stated more precisely, many of these innovations have acted as cultural buffers that have insulated or even protected farmers from the dangers and drawbacks of agriculture, which would otherwise have resulted in even stronger selection than we can detect.

What did we evolve to do?

• 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.