Food Intake and Choice PDF

Food Intake and Choice What does it have anything to do with Evolutionary Psychology? Why are we talking about Food, Ian? Does this look appetizing to you? How about this? The Importance of Food The defining feature of animals is that they must obtain food from living organisms in the external world...

Food Intake and Choice What does it have anything to do with Evolutionary Psychology? Why are we talking about Food, Ian? Does this look appetizing to you? How about this? The Importance of Food The defining feature of animals is that they must obtain food from living organisms in the external world Obtaining food is one of the six basic biological functions that engage behavior: – Breathing, excretion, sleeping, protection (avoiding harm), mating, and feeding – Eating Takes more time and thought than these other behaviors Plays a crucial role in biological and cultural evolution – Despite this, eating and food choice get little or not attention in Introduction to Psychology textbooks Aside from eating disorders, maybe The Importance of Food Food selection – Performed frequently in animals – Varies widely both across and within species (including humans) – Probably the most important psychologically relevant biological function regarding survival Food selection and accompanying changes in the environment – Generally cited as the most important forces in human biological and cultural evolution – Responsible for many facets of modern life Meat consumption and hunting The discovery and harnessing of fire for cooking The domestication of plants and animals The Importance of Food Two great problems that humans have faced – How to figure out, from an enormous number of options, what is toxic and what is nutritive This is termed “the omnivore’s dilemma” – How to coordinate the activities of multiple individuals to satisfy the needs of an omnivorous food-selection pattern Evolutionary biology and psychology have two explanatory components – First, to determine the adaptive value of a current behavior This is in terms of the ancestral environment in which it evolved – Second, tracing out over time how something came to appear in our species This is particularly tough for evolutionary psychology because behaviors leave few fossils Preadaptations, Co-Optations, and Exaptations Mayr (1960) proposed that the major source of evolutionary “novelties” is the co-opting of an existing system (preadaptation) for a new function (cooptation or exaptation) The co-optation can either replace an original function or add new functions to an existing system Preadaptations, Co-Optations, and Exaptations The food-relevant example is the human mouth – Teeth and tongue evolved for food handling They are now shared by the language expression system They are critical in pronunciation, but they did not (originally) evolve for that purpose Food itself has come to serve many functions – Originally only a nutritive function – Now serves aesthetic, social, and moral functions The Food Cycle The food cycle is a description of a sequence of activities that usually terminates in the consumption of food – – – – – Arousal Search Capture Preparation Consumption The Food Cycle Arousal – a motive for searching for an appropriate food item – Hunger is principally activated by a shortage (or anticipated shortage) of energy – Thirst is activated by a shortage of water, the most fundamental nutrient – A possible third system, sodium appetite, clearly exists in rats and some other animals May also exist in humans The Food Cycle Search (two components) – What to search for The identification of good candidates for ingestion Particularly important for a generalist (omnivore) animal – The pattern of search Where to look and when to shift from one foraging area to another The aim is to maximize energy input with respect to energy expenditure The Food Cycle Capture (once it is identified) – Could be trivially easy for some grazing animals – Could be difficult to access and require specific adaptations for others A giraffe has evolved a long neck Social hunting in wolves involves many highly honed social skills The Food Cycle Preparation of food for consumption – Again, for grazing animals or insect eaters, this is minimal – For other animals, it is a critical challenge Oyster drillers have to make holes in the oyster shell to obtain the meat inside Many mammals and some birds need to crack shells The Food Cycle Consumption – Vitally important, but usually less interesting For humans, it can be an elaborate and social activity The Food Cycle An animal’s adaptations to its food world will elaborate different phases of the food cycle – For the specialist (an animal that eats only one small class of foods) Identification can be innate (e.g., bamboo leaves for a panda) Preparation and consumption is straightforward – Carnivores eat a wider class of foods, but they can be encoded in a simple way e.g. for some species of frogs, if it is small and moving, it is food – There are adaptations needed for Capturing prey (e.g., the speed of a cheetah) Identifying vulnerable prey (e.g., the vision of an owl) Deciding where to forage The Omnivore’s Dilemma Omnivores consume both animal and plant foods – There is an enormous set of food possibilities – No way to prespecify What is edible from what is not What is toxic from what is not So, learning is required, but with some biological predispositions Omnivores have two additional problems – It is usually more challenging for them to find and capture their animal foods – Animal foods are more likely to harbor dangerous pathogens – The omnivore must Avoid plant poisons Avoid harmful micro-organisms contained in animal flesh The Omnivore’s Dilemma Omnivores face the greatest psychological food challenges – The return from this challenge, though, is the ability to live almost anywhere It’s no accident that three of the great omnivores are found all over the world – Humans, rats, and cockroaches Deciding What to Eat We have a variety of evolved mechanisms to assess edibility – Innate predispositions for identifying food – Neophobia and neophilia – Learning what is edible and what is not Innate Predispositions for Identifying Food Humans (and rats) at birth have an acceptance of sweet-tasting fluids – This is highly adaptive, since sweetness is most associated with fruit (a major source of nutrition) Human infants show an innate aversion to bitter and sour tastes – The bitter avoidance is adaptive since many common plant poisons are bitter There is a genetic preference for moderate levels of salt (sodium) that emerges well after birth – Salt is a vital nutrient that is in short supply in many environments There is a genetic positive response to fatty textures – Fat is one of three major macronutrients There is a genetic aversion to oral irritants, such as chili pepper – Not clear why humans have this, as many irritants in the environment are nutritive and have become major parts of human cuisines Each of these evolved taste biases have been demonstrated in rats and in a range of primates Neophobia and Neophilia Any new food has the potential to be an addition to the diet or toxic – For this reason, there is a clear conflict about sampling new foods Rats consume small amounts of new foods, allowing for the assessment of their effects Neophobia – the tendency to avoid new foods Neophilia – the tendency to approach new foods There is great variation in both neophobia and neophilia among humans – Both, are significantly heritable Learning What is Edible and What is Not Taste aversion doesn’t fit neatly within the confines of classical (Pavlovian) conditioning – This is because we get sick hours after we have consumed something – Behaviorists believed that the unconditioned and conditioned stimulus must be pair for learning to take place John Garcia discovered a way in which animals are far better learners than any classical behaviorist would expect Learning What is Edible and What is Not The “Garcia Effect” – Exposed rats to stimuli that have distinctive tastes and smells (like sweetened water) – Gave them toxins or radiation that made them sick hours later – As he predicted, these rats came to avoid the water with that flavor They developed an aversion to it – If Garcia tried to associate something other than a food with the sickness (e.g., a light or a tone), the rat developed no aversion This was unexpected from the standpoint of classical conditioning which – Requires multiple trials when the conditioned stimuli and unconditioned stimuli are presented at the same time – Found that the type of stimulus doesn’t matter This sort of learning makes perfect sense from an evolutionary perspective Learning What is Edible and What is Not Upper gastrointestinal events, particularly nausea, are critical consequences producing learned taste aversions Nausea following food ingestion results in a dislike for the relevant food – This is true even after a delay – Other negative visceral events (e.g., pain or allergy symptoms) don’t lead to dislike Sickness in Pregnant Women Pregnancy sickness – A heightened sensitivity and a nauseous reaction to particular foods Known as “morning sickness” – Reported in 75% to 89% of women – Actual vomiting occurs in 55% – If food aversions are included within the definition, it affects close to 100% of women during the first trimester The term “sickness” implies that something is malfunctioning… – Evidence suggests the opposite… Sickness in Pregnant Women The Embryo Protection Hypothesis (Profet, 1992) – States that pregnancy sickness is an adaptation that prevents mothers from consuming and absorbing teratogens Teratogens – toxins and other agents that might be harmful prenatally to her developing embryo Sickness in Pregnant Women Toxins occur in a variety of plants, many of which we consume regularly – e.g., apples, bananas, potatoes, oranges, and celery – The black pepper that we use to spice our food contains safrole Safrole is carcinogenic (causes cancer) and mutagenic (causes mutations) Primary problem faced by humans (and becomes more pronounced during pregnancy) – How to get the valuable nutrients from plants without incurring the costs of their toxins Sickness in Pregnant Women Plants and the predators that consume them seem to have coevolved – Plants signal their toxicity with chemicals Many get their strong taste from allyl isothiocyanate – These include cabbage, cauliflower, broccoli, and brussels sprouts Rhubarb leaves contain oxalate Humans find these chemicals bitter and unpleasant – These are adaptations that help them avoid consuming toxins Sickness in Pregnant Women Tierson, Olsen & Hook(1985) – Specific foods pregnant women report finding distasteful Coffee – 129 (out of a sample of 400) Meat – 124 Alcohol – 79 Vegetables – 44 – In contrast Only 3 women reported aversions to bread Not a single woman reported an aversion to cereals Sickness in Pregnant Women Dickens & Trethowan (1971) – Sample of 100 women 32 described aversions to coffee, tea, and cocoa 18 described aversions to vegetables 16 described aversions to meat and eggs Many became nauseated when smelling fried or barbecued food – These contain carcinogens Some nearly fainted when smelling spoiled meat – This was teeming with toxin-producing bacteria – If women consume these foods, they are likely to vomit Prevents the toxins from entering the mother’s bloodstream Prevents the toxins from passing through the placenta to the developing fetus Sickness in Pregnant Women Evidence supports Profet’s hypothesis that pregnancy sickness is an adaptation to prevent the ingestion of teratogens – The foods pregnant women find repugnant are those carrying the highest doses of toxins Meats, for example, often contain toxins due to fungal and bacterial decomposition Women seem to have a specialized meat-avoidance mechanism during the first trimester – Pregnancy sickness occurs precisely at the time when the fetus is most vulnerable to toxins This is roughly 2 to 4 weeks after conception, when many of the fetus’s major organs are being formed – Pregnancy sickness decreases around the eighth week and generally disappears entirely by the 14th week This coincides with the end of the sensitive period for organ development Sickness in Pregnant Women Perhaps the strongest piece of evidence for Profet’s hypothesis comes from the success of the pregnancy itself – Women who to not have pregnancy sickness during the first trimester Roughly three times more likely to experience a spontaneous abortion than women who do not experience such sickness – Yerushalmy & Milkovich (1965) Study of 3,853 pregnant women – Only 3.8 percent who experienced pregnancy sickness had spontaneous abortions – 10.4 percent who had not experienced pregnancy sickness had spontaneous abortions Fire and Cooking Carmody and Wrangham (2009); Wrangham et al. (1999) – Advanced the hypothesis that cooking was one of the keys to the emergence of modern humans – Most non-cooked foods Highly fibrous Provide relatively few calories compared to the effort needed to chew and digest them – Cooking Renders fibrous fruits, tubers, and raw meat more easily digestible Frees up energy Reduces the cost of digestion Kills off microorganisms that could be toxic to humans – 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 Fire and Cooking Evidence supporting Wrangham’s cooking hypothesis – Cooking food provides a predictable increase in its net energy value – Cooking renders food more easily digestible – Cooking is a human universal – The human brain requires a tremendous number of calories to function Fibrous fruits and other raw foods rarely can provide enough – On exclusively raw-food diets, humans fare poorly Among women, they may lose the ability to reproduce Why Humans Like Spices Humans must eat, but eating poses survival dangers – Ingesting things from outside the body provides an avenue for entry of dangerous microorganisms and toxins that can cause sickness or death – These hazards are present in almost everything we eat Most of us have experienced being – “Sick to my stomach” – Vomiting because of food poisoning Why Humans Like Spices We can minimize these dangers in today’s environment – But imagine the time of our ancestors… Before refrigerators Before artificial preservatives When food was scarce and sanitation standards were lower – One obvious solution is cooking This kills off most microorganisms – Another potential solution is the use of spices Why Humans Like Spices Spices come from plants – Flowers, roots, seeds, shrubs, and fruits Spices emit unique smells Spices have specific tastes due to “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 Why Humans Like Spices Sherman and Flaxman (2001) – The Antimicrobial Hypothesis states that spices help humans avoid becoming ill or poisoned by the foods we eat Spices kill or inhibit the growth of microorganisms Spices prevent the production of toxins in the foods Why Humans Like Spices Evidence for the Antimicrobial Hypothesis – Of the 30 spices for which we have solid data, all killed many of the species of foodborne bacteria on which they were tested The most powerful were onion, garlic, allspice, and oregano – More spices, and more potent spices, tend to be used in hotter climates Unrefrigerated foods spoil more quickly in hotter climates – This promotes the rapid proliferation of dangerous microorganisms – More spices tend to be used in meat dishes than vegetable dishes This is because dangerous microorganisms proliferate more on unrefrigerated meat Dead plants, in contrast, contain their own physical and chemical defenses and are thus better protected from bacterial invasion Why Humans Like to Drink Alcohol Primates have been eating fruit for at least 24 million years The ripest fruits, which are generally preferred, contain high amounts of – Sugar – Ethanol “Ethanol plums” emitted by fruit provide a cue to its ripeness Primates have been consuming low levels of ethanol for millions of years through ripe fruit Why Humans Like to Drink Alcohol Modern humans live in a world that is far removed from the low level of ethanol consumption of the past – Ethanol levels in fruit are typically only 0.6% – Ingestion of fruit might yield a blood ethanol level of only 0.01% This is far lower than the typical legal definition of drunk, which is 0.08% Our distant ancestors didn’t have the kegs of beer, bottles of wine, or flasks of whiskey that contain high concentrations of alcohol Why Humans Like to Drink Alcohol The Frugivory By-Product Hypothesis – States that the human penchant for drinking alcohol is not an adaptation, but rather is a byproduct of the adaptive fondness for ripe fruit “Alcohol not only has a distinct taste but it also has a unique odor and is often associated with the color and fragrance of ripe fruits… Utilizing the odor and taste of alcohol enables the animal to predict the caloric value of a food.” Singh (1985)