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Chapter 3

CHAPTER 3 NOTES - Evolutionary Psych

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York University
PSYC 3420
Irwin Silverman

COMBATING THE HOSTILE FORCES OF NATURE HUMAN SURVIVAL PROBLEMS • Differential production is the "bottom line" of the evolutionary process, the engine that drives natural selection • Darwin summed it up as: "As more individuals are produced than can possibly survive, there must in every case be a struggle for existence, either one individual with another of the same species, or with the physical conditions of life" • Everyone has at some point encountered forces that endanger survival, Darwin called these the "hostile forces of nature", and they include: climate, weather, food shortages, toxins, diseases, parasites, predators, and hostile conspecifics (members of the same species) • Each of these hostile forces has created adaptive problems for humans • Scientific work over the past decade has indeed shown that humans universally appear to have a fairly sophisticated "folk biology" • The core of this folk biology is the intuition that living things come in discrete packets that correspond to distinct species and that each distinct species has an internal "essence" that produces its growth, bodily functions, external form, and special powers o Ex. Nettles have an internal essence that produces thorns that can sting you o Ex. Lions have an internal essence that produces canine teeth and specialized claws to kill • Folk biology appears to emerge early in life and is universal across cultures o Ex. Young children show beliefs about the internal essence of species. They believe, if you remove the insides of a dog, it loses its "essence" and is no longer a dog, because it can't bark or bite. But if you remove its outsides or change its external appearances so that it doesn’t look like a dog, children still believe that it has retained its essential "dogness" • It's likely that the universal folk biology, with the core belief that different members of the same species share hidden causal essences, is an evolved cognitive adaptation o Emerges early in life without any given instructions from parents o Universal across all cultures o Central to solving many of the survival problems FOOD ACQUISITION AND SELECTION • Diet is the primary factor allowing or constraining the rest of a species' system of adaptations • Most animals spend more waking hours searching, capturing, and intaking food than any other activity • Finding food is necessary for survival as finding a mate is for reproduction • The most pressing general problem in food selection is how to obtain adequate amounts of calories and specific nutrients (ex. sodium, calcium) without at the same time consuming dangerous toxins that could rapidly lead to death; this requires: o Searching for food o Recognizing, capturing, handling, and consuming it o Digesting to absorb its nutrients • The problem of food selection become especially crucial for omnivores (eat plants AND animals) CHAPTER 3 page 1 o Ex. Rats and humans o Eating a wide range of foods, increases one's odds of being poisoned because toxins are widespread throughout the plant world • Evolutionary insight: plants toxin themselves are adaptations that reduce the offs of the plant being eaten • Toxins, thus help plants defend themselves from predators, but they hurt humans and other animals that rely on the plans for survival SOCIALAND CULTURALASPECTS OF FOOD • The sharing of food is a major social activity for humans • Sharing food is also a strategy of courtship, a sign of closeness of relationships, and a means for reconciling after a conflict • Fishermen tell tales about the fish they catch, farmers about the size of their vegetables, hunters about their prowess in taking down large animals • Failure to provide food can lead a man to lose status in the group • It's not uncommon for women in some tribes to divorce husbands who fail to provide food • Even the myths and religions of cultures about with stories of food and drink • Food and its consumption have become frequently used metaphors (ex. A good juicy book) • Food permeates our psychological preoccupations, verbal discourse, social interaction, and religious beliefs on a daily basis FOOD PREFERENCE • All over the world, people spend more money on food than anything else • People in western countries spend 21% of their income on food, second only to income spend on leisure activities • In less wealthy countries 50% of all income is spent on food • Worldwide, however, food takes center stage in parent-infant interactions • Humans have an evolved taste preferences for sweet foods, which provide rich sources of calories • We also dislike bitter and sour foods, which tend to contain toxins • Experiments show that rats display an immediate liking for salt the first time they experience a salt deficiency • They likewise increase their intake of sweets and water when their energy and fluids become depleted • These appear to be specific evolved mechanisms, designed to deal with the adaptive problem of food selection, and coordinate consumption patterns with physical needs • Both humans and rats have an adaptation called xenophobia, defined as a strong aversion to new foods • Rats typically, sample new and unfamiliar food only in very small do so, they eat the new foods separately - never together CHAPTER 3 page 2 • When a rat eats both a familiar food and a new food at the same meal and gets sick, it avoids only the new food • It seems to "assume" that the familiar food is safe and the new food is the source of the sickness DISGUST: THE DISEASE-AVOIDANCE HYPOTHESIS • The emotion of disgust is a hypothesized adaptation that serves as a defense against microbial attack, protecting people from the risk of disease • Disgust is an emotion that involves feelings of revulsion and sometimes nausea • It motivates strong withdrawal from the disgust-producing stimulus • If the emotion of disgust is an evolved defense against disease, several predictions follow: a. Disgust should be evoked most strongly by disease-carrying substances b. These disgust elicitors should be universal across cultures • A cross-cultural study asked Americans and Japanese to list the things they found most disgusting o Feces and other body wastes were the most frequently mentioned items, at 25% of the written responses • Another study found that students refuse to drink from a glass that has been thoroughly cleaned and sterilized when told that it had once held dog feces • Other evidence of the universality of disgust comes from studies that find that the facial expression of disgust is universally recognized; it's expressed by people who are blind from birth; and it is interpreted correctly by people who are born deaf • Another prediction from the disease-avoidance hypothesis of disgust is a gender difference: o Since women typically care for their infants/children, they need to protect them from disease, as well as themselves o And indeed women find images depicting disease-carrying objects to be more disgusting than mend do, and also perceive that the risk of disease is greater from those objects than men do • A direct evidence of the protective function of disgust: o Individuals who have specially heightened sensitivity to contamination and who were most easily disgusted have significantly fewer infections • Potential contact with people who have poor hygiene, who appear diseased witnessing body boundary violations such as a gaping wound, and who have certain sex practices such as anal sex, often provoke disgust • It is an emotion that evolved to avoid predictable classes of disease conduits that jeopardized survival • There are some situations in which it would be advantageous to turn off or supress the disgust reaction to solve other adaptive problems, such as caring for a wounded ally or a close kin member • In an experiment, mothers asked to smell feces from different infants, mothers rated feces from their own infants as considerably less disgusting that feces from other infants, even when the feces samples were intentionally mislabelled CHAPTER 3 page 3 SICKNESS IN PREGNANT WOMEN: THE EMBRYO PROTECTION HYPOTHESIS •During the first 3 months of pregnancy, some women develop pregnancy sickness - heightened sensitivity and morning sickness •About 75-89 % of women experience nauseous reactions to foods •About 55% of women vomit • If food aversions are added to the definitions of pregnancy sickness, then close to 100% of all pregnant women would report pregnancy sickness during the 1st trimester •Profet hypothesizes that pregnancy sickness is an adaptation that prevents mothers from consuming and absorbing teratogens - toxins that might be harmful to the developing baby •The black pepper that we use to spice up our food contains safrole, which is both carcinogenic (causes cancer) and mutagenic (causes mutations) •The special problem that humans face, which becomes more pronounced during pregnancy, is how to get the valuable nutrients from plants without at the same time incurring the costs of their toxins •Plants and predators that consume them seem to have coevolved •Plants signal their toxicity with chemicals •Humans find these chemical bitter and unpleasant - an adaptation that helps them avoid consuming toxins •The specific foods pregnant women report finding distasteful include: coffee, meat, alcohol, and vegetables •In contrast, only 3 women reported aversions to bread, and not a single women reported aversions to cereals •In another experiment: of the 100 women, 32 described having aversions to coffee, tea, and cocoa; 18 to vegetables, 16 to meat and eggs •Vomiting prevents the toxins from entering the mother's bloodstream and passing through the placenta to developing fetus •Evidence supports Profet's hypothesis that pregnancy sickness is an adaptation to prevent ingestion of teratogens 1. The foods pregnant women find repugnant appear to correspond to those carrying the highest doses of toxins (ex. Meat) 2. Pregnancy sickness occurs precisely at the time when the fetus is most vulnerable to toxins, about 2-4 weeks of conception, which when many of the fetus's major organs are being formed 3. Pregnancy sickness decreases around the 8th week and generally disappears entirely by the 14th week, coinciding with the end of the sensitive period of organ development CHAPTER 3 page 4 • Women who don't have pregnancy sickens during the 1st trimester are roughly 3 times more likely to experience a spontaneous abortion than women who do experience such sickness • Most adaptations are expected to be universal, so cross-cultural is critical • Although pregnancy sickness has not been explored much in other cultures, the ethnographic record contains evidence of its existence among the Kung of Botswana, the Efe Pygmies of Zaire, and the Australian Aborigines • A recent study of 27 traditional societies revealed that pregnancy sickness was observed in 20, and not observed in 7 • The 20 societies which pregnancy sickness was observed were far more likely to use meat and other animal products, which typically contain pathogens and parasites at higher rates than do plants • More extensive cross-cultural research is clearly needed to test the embryo protection hypothesis • Profet's analysis of pregnancy sickness highlights one of the benefits of adaptations thinking FIRE AND COOKING • At least one aspect of food consumption is unique among modern humans - we build fires and cook our food • Richard Wrangham has advanced the hypothesis that cooking was one of the keys to the emergence of modern humans • According to the cooking hypothesis, the invention of fire and the ability to cook provided the key evolutionary impetus for the evolution of extraordinarily large human brains • Evidence supporting Wrangham's cooking hypothesis includes: 1. Cooking food provides a predictable increase in its net energy value 2. Cooking renders food more easily digestible 3. Cooking is a human universal 4. The human brain requires a tremendous number of calories to function, and fibrous fruits and other raw foods rarely can provide enough 5. On exclusively raw-food diets, humans fare poorly, and among women, many lose the ability to reproduce • The cooking hypothesis is controversial among scientists • One of the key issues hinges on when the intentional use of fire entered the human repertoire • For Wrangham's hypothesis that cooking was the key invention that led to large human brains to be correct, cooking had to be widely used 1.6 -1.9 million years ago, when our Homo Erectus ancestors appeared in the fossil record with substantially larger brains than their predecessors • The evidence for the controlled use of fire that long ago is thin WHY HUMANS LIKE SPECIES: THE ANTIMICROBIAL HYPOTHESIS • Humans have to eat, but eating poses dangers to survival • In today's environment we can minimize these dangers CHAPTER 3 page 5 •One solution is cooking, which kills off most microorganisms •Other solution is the use of spices •Spices emit unique smells and have specific tastes due to chemicals called "secondary compounds" •These compounds usually function in plants as defense mechanisms to prevent macroorganisms (herbivores, or plant-eating animals) and microorganisms (pathogens) from attacking them •According to the antimicrobial hypothesis, spices kill or inhibit the growth of microorganisms and prevent the production of toxins in the foods we eat and so help humans to solve a critical problem of survival: avoiding being made ill or poisoned by the foods we eat •Several sources of hypothesis support this: 1. Of the 30 spices for which we have solid data, all killed many of the spices of food-borne bacteria on which they were tested • Onion, garlic, allspice, and oregano are the most powerful in killing bacteria 2. More spices, and more potent spices, tend to be used in hotter climates, where unrefrigerated food spoils more quickly, promoting the rapid proliferation of dangerous microorganisms • Ex. In India, a typical meat dish uses up to 9 spices, whereas, in Norway, less than 2 3. More spices tend to be used in meat dishes than in vegetable dishes •It is more likely that eating certain spices was discovered by accident or experimentation; people discovered that they were less likely to feel sick after eating leftovers cooked with aromatic plant products WHY HUMANS LIKE TO DRINK ALCOHOL: AN EVOLUTIONARY HANGOVER? •Primates have been eating fruit for less than 24 million years •Most primates are primarily frugivorous - fruit is the mainstay of their diet •The ripest fruits, which are generally preferred, contain high amounts to two ingredients: o Sugar and ethanol •"ethanol plumes" emitted by fruit might provide cues to its ripeness •Primates, including humans, have been consuming low levels of ethanol for millions of years through ripe fruit •The ethanol levels in fruit are typically only 0.6 % •On the basis of a reasonable set of assumptions, ingestion of fruit might yield a blood ethanol level of only 0.01%, far lower than the typical legal definition of drunk, which is 0.08% •According to the frugivory by-product hypothesis, the human penchant for drinking alcohol is not an adaptation, but rather is a by-product of adaptive fondness of ripe fruit •Alcoholism might be a currently maladaptive by-product of the overindulgence of these frugivorous mechanisms THE HUNTING HYPOTHESIS CHAPTER 3 page 6 • Ancestral methods of securing food have been linked to the rapid emergence of modern humans • The importance of hunting in human evolution, for example, has been a major source of controversy in anthropology and evolutionary psychology • One widely held view is the model of "man the hunter" • According to this view, the transition from mere foraging to large game hunting provided a major impetus for human evolution, with a cascading set of consequences including a rapid expansion of tool making and tool use, the development of a large human brain, and the evolution of complex language skills necessary for communication on cooperative hunts • The initial impetus for the human shift to a diet high in meat may have been spurred by an ecological change that took place in Africa associated with global cooling a few million years ago • It produced a dramatic increase in open grassland, making plant food scarce and animals increasingly attractive as a food resource • Human groups consume far more meat than any other primate species • It is difficult for humans to get all essential nutrients, such as cyanocobolamine, from an exclusively vegetarian diet • This suggests that meat has been a central feature of the human diet for thousands of generations • Modern tribal societies often hunt as a major method for food acquisition • Our bodies are walking archives that show a long history of eat eating • The fossil record of teeth of human provides another clue to diet • All these clues suggest a long evolutionary history in which meat was an essential part of the diet of human ancestors • The Provisioning Hypothesis o Proponents of the hunting hypothesis argue that it can explain a large number of unusual features of human evolution o Perhaps most important, it can explain the fact that human males are unique among primates in their heavy parental investment in children (aka the provisioning hypothesis) o It is often regarded as an adaptive explanation for the evolution of hunting • The hunting hypothesis can also explain several other aspects that characterize humans 1. Emergence of strong male coalitions, which appear to be characteristic of humans worldwide 2. Emergence in humans of strong reciprocal altruism 3. Emergence of social exchange 4. Provides explanation for the sexual division of labour • Men's larger size, upper body strength, and ability to throw projectiles accurately over long distances make them well suited for hunting 5. Provides explanation for the emergence of stone tool use • The show-off hypothesis: Status competition among men CHAPTER 3 page 7 o Hunting produces resources that are unique among the food groups in two aspects 1. Meat comes in large packages 2. The packages are unpredictable o These qualities establish the conditions for the sharing of meat beyond the confines of one's immediate family, and these periodic "bonanzas" would become known to everyone in the community o This hypothesis proposed by Kristen Hawkes, suggests that women would prefer to have neighbours who are show-offs - men who go for the rare but valuable bonanzas of meat - because they benefit by gaining a portion of it • Men pursuing the risky hunting strategies would benefit in several ways: o By gaining increased sexual access to women, they increase the odds of fathering more children o The favored treatment of their children from neighbours increases the survival and possible reproductive success of those children • The show-off hypothesis can be considered a rival of the provisioning hypothesis, at least in its pure form o Men have hunted to provide for their families and to gain the status, sexual, and alliance benefits from outside their families • The Gathering Hypothesis o In contrast to the view that men provided the critical evolutionary impetus for the emergence of modern humans through hunting, an opposing view suggests that women provided the critical impetus, through gathering o According to this hypothesis, stone tools were invented and used not for hunting, but rather for digging up and gathering various plants o This hypothesis would explain tr
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