SPECIFICATION: Explanations for food preferences: The evolutionary explanation, including reference to neophobia and taste aversion.

The human capacity for taste is a complex and varied aspect of our sensory experiences, deeply intertwined with our survival, nutrition, and enjoyment of food. The ability to taste is not uniform across the population; individuals can be categorized into three primary groups based on the density of taste buds on their tongue: non-tasters, average tasters, and supertasters. This classification is determined by the number of papillae - the small bumps that house taste buds on the tongue and soft palate.

Each taste bud contains 30-100 receptor cells that respond to tastants; the chemicals in foods are perceived as five main taste sensations: sweet, salty, sour, bitter, and umami (savoury). This sensory information is then relayed to the brain, creating our perception of flavour. However, taste is just one flavour component; our food experience is also significantly influenced by other senses, especially smell and touch.

The distribution of tasters in the population is noteworthy, with about one in four people being non-tasters (having fewer than 15 papillae), one in two being average tasters (15-35 papillae), and another one in four being supertasters (more than 35 papillae). This variation in taste sensitivity can have significant implications, from food preferences to nutritional choices.

Interestingly, a substantial portion of taste disorders is smell disorders, given the critical role of olfaction in flavour perception. Loss of smell or taste can pose serious safety risks, such as the inability to detect smoke or spoiled food.

The evolution of taste perception, particularly the sensitivity to bitter tastes, is believed to have been a defence mechanism against consuming toxic substances in some plants. This is supported by the discovery that variations in the TAS2R38 bitter taste receptor allow for the detection of glucosinolates, compounds that can be harmful if consumed in large quantities.

Genetic factors are crucial in taste perception, influencing how individuals react to different flavours. For instance, a heightened sensitivity to sour tastes may make certain foods less appealing to some, while others may find them enjoyable. Each type of taste bud – sour, umami, and sweet – serves a specific function, from signalling the freshness of the food to identifying essential nutrients.

Understanding the intricacies of taste perception and its genetic underpinnings opens the door to potentially manipulating diets to encourage healthier eating habits. By catering to individual taste preferences, it may be possible to design more appealing and nutritionally balanced diets, promoting overall well-being and addressing dietary concerns at a personalized level.

CO EVOLUTION AND EATING PREFERENCES

Coevolution, in the context of human development and diet, encapsulates the intertwined evolution of human populations and their surrounding ecosystems, including the foods those environments offer. This dynamic process highlights the mutual adaptation of humans and their dietary sources over millennia, shaped by geographical, environmental, and societal factors. As human populations migrated and settled in diverse habitats around the globe, they encountered distinct challenges and opportunities in terms of available food sources. Over generations, these environmental pressures led to evolutionary changes, both in the humans adapting to make the most of their available diets and in the cultivation or domestication of plants and animals that best suited human needs

Dairy Tolerance: In many Western societies, the consumption of dairy products is widespread, attributed to historical adaptations to livestock farming. The ability to digest lactose in adulthood, known as lactase persistence, provided a selective advantage in regions where milk from domesticated animals became a crucial part of the diet. This adaptation allowed individuals access to a nutritious and energy-rich food source during times of scarcity. In contrast, many Asian and African cultures lack this adaptation because dairy farming did not historically form the basis of their diets, resulting in a higher prevalence of lactose intolerance among these populations.

Testing for specific enzymes related to lactose intolerance and alcohol flushing can offer insights into an individual's genetic makeup and ancestral dietary adaptations. Research indicates that the ability to flush alcohol, often resulting in a red facial reaction, is linked to a deficiency in the ALDH2 allele, a genetic variant affecting alcohol metabolism.

Lactose tolerance varies significantly across global populations, largely influenced by their ancestors' dietary practices, particularly livestock agriculture. For instance, in Northern Europe, where dairy farming has a long history, about 95% of adults can digest lactose effectively. In contrast, regions of Asia, where livestock agriculture is a more recent development, show less than 10% lactose tolerance among adults.

Bloom and Sherman further elaborate on this topic by exploring how the prevalence of lactose intolerance correlates with the historical spread of contagious diseases among cattle. Diseases affected the viability of cattle herding as a sustainable food source, which, in turn, impacted the evolutionary pressure on human populations to adapt their digestive systems to process lactose. Herding was less common in areas where cattle diseases were rampant, reducing the selection pressure for lactose tolerance. This evolutionary perspective highlights how historical, environmental, and genetic factors intertwine to shape human dietary capabilities and intolerances.

Alcohol Adaptation: The development of alcohol tolerance can also be seen as an adaptive response to environmental conditions. In crowded urban environments where water contamination was a significant risk, consuming fermented beverages offered a safer alternative to potentially infected water sources. The alcohol in these beverages helped prevent the spread of diseases, offering a survival advantage. However, the alcohol flush reaction, characterized by severe physiological responses to alcohol consumption, is prevalent in many Asian cultures. This condition suggests a genetic predisposition that affects alcohol metabolism, illustrating how genetic variations can influence dietary tolerances and preferences across different populations

Evolutionary Explanations for food preference.

Evolutionary origins of the human diet and our preference for: meat (including its influence on brain size, societal change, and gender division); fat, sugar/carbohydrates and salt.

 

Evolutionary theory says that organisms (humans are included in this description!) need to maximise the survival of their genes so they maximise the chance of having offspring that survive. Behaviour should have survival value. This is very applicable to our diet/food. What we evolved to eat in the EEA should have increased our chance of survival.

 

·      The “ultimate explanation”

·      Eating behaviour that might not make sense today may have an evolutionary basis...

·      Our ancestors lived in an Environment of Evolutionary Adaptation (EEA)

·      Natural selection favoured adaptations geared towards survival

·      Interactionist approach (nature + nurture): genes are shaped by the environment or  also known co-evolution

What do we Like (and not like)?

·      Sweet – identify foods rich in carbohydrates to provide us with energy

·      Sour – associated with food that has gone off and therefore, should be avoided

·      Salt – critical for functioning of the cells and therefore need to identify

·      Bitter – associated with poisonous plants, should be avoided

• Umami – a recent discovery which is highly savoury – a meaty taste

Preference for High-Fat Foods

Fat contains twice as many calories per gram than do proteins or carbohydrates. Thus it is easy to see how humans (and other animals) would learn at an early age to prefer high-fat foods. Such foods were not easy to find in the environment in which humans evolved so finding it would have been a rare treat that had survival value, e.g., calorie dense. Fat would have come from animals. Wild animals are nor fat. Any fat eaten would have been shared amongst family members so no danger of being able to over do eating fat.

A02 commentary

However, these foods are now easily and cheaply available in industrialized countries such as the United States. Thus, in our current environment, our preferences for high-calorie food make it very difficult to keep fat consumption low, as recommended by the Surgeon General (U. S. Department of Health and Human Services, 1988). With regard to calorie consumption, humans are adapted to a different environment than the one in which we live. It is this mismatch that results in our behaving in seemingly unadaptive ways.

A01 research:

Starved chimpanzees will go straight for the brain or bone marrow of an animal. These parts are the fattiest. Obviously monkeys may not be directly comparable to humans.

The increased levels of obesity in the developed world would suggest that people as predicted by EP find it hard to ignore high fat food offerings when they are readily and cheaply available.

Why the preference for sweet foods?

In some ways the answer to this is obvious.  Sweet indicates presence of sugar which indicates calories needed for energy.  Sweetness would be associated with foods that are ripe and foods that are ripe are going to contain more sugar. In addition to sugar, fruit provides many vitamins and minerals necessary for body function and growth. A preference for sweet foods and drinks that would encourage consumption of ripe fruit was probably advantageous to our early ancestors (Konner, 1988). Thus it would have been adaptive for humans and other omnivores to have evolved with a preference for the taste of sweet. In fact, there is much evidence suggesting that this is the case.  Rozin (1982) thinks this preference for sweetness is innate.  Moreover, sweet foods and carbohydrates add weight and weight is necessary for survival. The EEA was harsh and dying from famine was common. This applies to our love of fat too.

A01 research:

This would seem to be supported by the number of sweet receptors on the human tongue, far more than for the other flavours such as bitter, sour, salt and umami.  People of all ages and of all cultures seem to prefer sweet taste to any other, suggesting it is an inherited preference: Meiselman et al (1989)

Bell et al (1973) gave sweet foods to Eskimos in Alaska. Under normal conditions Eskimos have nothing sweet in their diet.  However, the foods were readily accepted despite their novel nature, again suggesting an underlying human preference for sweet foods.  Human babies also love things that are sweet and will eat them the first time they are encountered.

First, people of any age are likely to pick sweet foods over others (Einstein & Hornstein, 1970).This is also frequently true of many other species, such as, horses, bears, and ants (Capaldi).

Many pieces of data suggest that early exposure to the taste of sweet is not necessary for there to be a preference for the taste of sweet. For example, 1- to 3-day-old human infants prefer sweet over nonsweet fluids (Desor, Maller, 1973).

Further, newborn infants, without any prior breast or bottle feeding, show an acceptance response the first time that they taste sweet. This response involves what appears to be a slight smile, licking of the upper lip, and sucking. This acceptance response is apparently an innate, reflexive response that is designed in such a way that whatever substance elicits the response will tend to be ingested. Rats also show this response when they taste sweet (Grill & Norgren, 1978; Steiner, 1977).

Desor et al (1975) investigated babies’ food preferences based on facial expressions and sucking behaviour. Newborn babies demonstrate innate preference for sweet tasting food. Babies reject bitter tasting substances.

A02 for Desor (1975)

• Lab (controlled) observations – controlled but may lack ecological validity

• Questionnaires and food diaries – insight into PPs real life BUT may be inaccurate + recording eating might actually change eating behaviour in PPs

• Naturalistic observation – risk of Hawthorne effect + difference between public and private eating behaviour

• Reductionist and determinist (eating is caused by events happened years ago)

• Can explain innate food preferences

• Gives an explanation that can account for both nature and nurture

• Difficult to falsify, so questionable validity

• Focuses on ultimate rather than proximate causes could provide more effective intervention strategies-has human evolution stopped or are we still adapting?

Finally, rats can be selectively bred to have a greater or lesser preference for sweet (Nachman, 1959). The fact that this is possible shows clearly that genes can play a role in the preference for sweet in rats. However, this does not, of course, necessarily mean that genes make a significant contribution to the preference for sweet in humans.

Preference for Salty Foods. Similar to calories, salt is essential for the body to function properly. This is true for humans as well as for other species. Many physiological functions depend on the presence of salt, and even on a particular concentration of salt (Bloch, 1978; Denton, 1982). For example, the concentration of salt in the blood must be kept at a specific level as it is essential for the functioning of muscles and nerve cells (action potentials and all that).  Homeostasis keeps salt levels reasonably constant. In humans, small amounts of salt are lost continually through sweat and through the action of the kidneys. If someone ceased to ingest salt, the body would excrete water in an attempt to keep the concentration of salt in the blood at the optimal level. Eventually that person would die of dehydration (Block, 1978).

Although salt is necessary for the body to function properly, it is not easily available in the wild so like fat when it was found by our ancestors it would have been much prized, hence the reason for us liking it so much.  Some have suggested that our desire for salt is innate, we do after all have salt receptors on the tongue. 

However, unlike sweet, our taste for salt doesn’t seem to evolve until we’re a few months old, suggesting a predisposition but with a learned component.  Not until the age of about 4 months does the taste seem to develop and by the age of two years children will reject food that they’re expecting to be salty that isn’t. 

Food producers have been accused of taking advantage of our ancient desire for salt by adding it in overly liberal quantities in processed foods.

A01 Research:

The evidence strongly supports this hypothesis, although the situation is somewhat different from that of the preference for sweet. Unlike the preference for sweet, human infants are not born preferring salt. This is because humans cannot taste salt well until approximately 4 months of age, at which point they demonstrate a preference for salty over non-salty solutions. Then, by around 24 months of age, children have learned which foods are supposed to be salty, and they reject foods that do not contain the customary degree of saltiness.

A02 conclusion salt

As people get older, it is possible to decrease their need-free preference for salt to some extent by giving them weeks of experience only with foods with relatively low salt content (Beauchamp, 1987).

Thus, as for the preference for sweet, the preference for salt appears to be virtually universal and to have a substantial genetic component. However, it is possible to influence the preference for salt by experience. Also similar to the preference for sweet, although the preference for salt was probably adaptive in the environment in which we evolved, it is no longer adaptive.

Preference for meat

·      Humans split from the great apes about 6 million years ago.  Modern apes live on nuts, fruit and plants.  Therefore likely our early ancestors were vegetarian.

·      However, we rapidly became omnivores and this is evident in modern hunter-gatherer societies.

·      Our digestive system is different from monkeys and apes as theirs is specialised for the digestion of plant material.

Evolutionary psychologists (and many other researchers) believe that our ancestors also started eating meat in substantial quantities between 1.9 and 1.6 million years ago. Considerable debate revolves around the hypothesis that a shift to meat eating played a role in the evolution of brain size. It is not clear whether the increased brain size led to demands that were met by meat eating or that a shift to meat eating permitted the increase in brain size. It's also possible that meat eating and brain size are not directly causally related, but there is strong evidence that the two are associated with each other.

Primates, especially humans, have large brain size relative to body size when compared with other placental mammals. In humans this dramatic increase in brain size has occurred in the last 4.5 million years. What was the evolutionary factor that led to this increase?

What we know is two requirements had to be met in order to achieve this large brain:

·      The brains chemical requirement for Polyunsaturated Fatty Acids, had to be met

·      Increased metabolic demand

The fatty acids mentioned are the major structurally significant and biochemically active components of the grey matter of all mammalian species. The availability of these may have provided the ingredients necessary to increase brain size. Because little of these fatty acids are found in plants, in order to achieve large brain size, it would have required us to be eating meat! Could meat consumption have been the driving force for our large brains? More evidence follows.

The metabolic demand of the brain is nine times that of the whole human body.

Helped tools use

It was hard for a primate with a humanlike digestive system to satisfy its protein requirements from available plant resources. The Homo habilis had developed a requirement for protein and with their digestive system; they were not able to get that from the available plant resources. While leaves and legumes are high in protein, they contain substances that cause the proteins to pass through the body without being absorbed. Thus, in addition to plant resources available, the major new source was animal protein, which came from fatty marrow and whatever other edible leftover flesh remained in and on the bones of the dead animals (Havilland,). While the early humans developed the need for meat in their diet, they lacked the teeth necessary to rip and cut the flesh of animals. Thus, it was necessary to produce tools in order to obtain and prepare the meat needed for their diet. The use of tools allowed Homo Habilis to change slowly from scavenger to predator.

A01 research

• Dietary quality is correlated with brain size.

• Foley and Lee first consider brain size vs. primate feeding strategies, and note that folivorous diets (leaves) are correlated with smaller brains, while fruit and animal foods (insects, meat) are correlated with larger brains.

• Modern researchers have a pretty good idea of what our ancestors ate.  Cave drawings, like the ones found in Lascaux in France depict food of the day. 

• Ancient skulls bear clues in the form of patterns of wear and tear on the teeth.

• Nitrogen and carbon in bones show we ate meat enable us to judge the age of findings

• Canine teeth in humans

• Smaller digestive system geared towards meat.

• Correlation of anthropological evidence of eating meat and increase in human brain size.

• Human brain's metabolic budget significantly different from apes. They point out that anthropoid primates use ~8% of resting metabolism for the brain, other mammals (excluding humans) use 3-4%, but humans use an impressive 25% of resting metabolism for the brain. This indicates that the human "energy budget" is substantially different from all other animals, even our closest primate relatives--the anthropoid apes.

·      Even in human populations where meat consumption is low, IQ is still much higher than in other large-bodied primates because grains are much more calorically dense than foliage.

Other intellectual gains that Evolutionary theory see as being the result of a meat based diet. (hard to prove though).

1.     Social skills leading to language and high level skills

2.    Hunting required specialised skills

3.    Co-operation between group members (hunting, altruism, bartering) e.g. meat for sex hypothesis)

4.    Geographical skills

5.    Tool use, to enable eating meat or killing of an animal

6.    Divisions of gender roles

7.    These skills would mean larger brains would be selected

8.    Buss (2008) reports than in some modern hunter gatherer societies women will divorce men who do not provide food

A02

Determinism: We are determined to follow the diet of our ancestors, e.g., meat, carbohydrates, fats. ET suggests we are predestined to like especially fatty and sweet foods. Are we? People diet or follow different eating plans, low carbohydrates, macro diet, veganism; low calorie etc does not explain vegetarianism though (ironically it takes intelligence to consider the morality of eating animals and vegetarianism, something that probably would not have been possible without our ancestors eating meat and increasing our brain size)..

 

Reductionism: Reduces our food preference to evolutionary ideas of survival and adaption. Probably right in this instance however, not all people have the same food preferences: Eskimos don’t eat sugar, the Japenese eat a great deal of starchy food, Jains are vegetarian etc gain weight. Are genetic or cultural factors involved too? Maybe people have different constitutions because they evolved in different places. Human food preferences are remarkably varied, both within and between populations. This does not mean that variation is entirely cultural or learned, because genes and culture may co-evolve to determine variation in dietary habits.

 

This co-evolution has been well documented in some cases, such as lactose tolerance (inability to digest dairy products in adults - This is found in many Asian and African cultures, where industrialized and commercial dairy products are uncommon), but is less well understood in others, such as in Favism (a hereditary disorder involving an allergic-like reaction to the broad, or Fava, bean - haemolytic response) in the Mediterranean and other regions. The Japanese diet is very high in starch (a complex carbohydrate) due to their love of rice.  The Japanese genome seems to have adapted to this by producing extra copies of AMY1, a gene responsible for the production of amylase (enzyme that digests starch). The Yakut or the Arctic, have a low carb diet, preferring to indulge on the plentiful supplies of fish in the area.  These have fewer genes for the production of amylase. 

Culture, therefore may be having an impact on human biology, as we adapt to various diets due to the myriad of conditions in which we are capable of thriving.

Evolutionary explanations of human food preference is accepted by the scientific community as fact (with a few exceptions).

 

The evidence is clear and testable and supports the idea of slow change over long periods of time. The latest techniques for analysing carbon and nitrogen isotopes in hominid bone have confirmed that our ancestors were eating meat.

 

Changes in anatomy: shorter intestine, longer duodenum, defunct appendix, changes in teeth (e.g. canine for biting) bigger brain size have coincided with changes in diet, such as a move to eating more meat. Correlations don’t show cause and effect yet there is no other plausible theory on offer.

 

The way our senses are organised such as smell and taste receptors is logical and reasonable there are no other convincing theories that explain rationally why they exist. ET theory suggests they exist because it helps us recognise sweet foods which were good for us because of fruit/vitamins minerals and cbecause of Carbohydrates. Also tongue helps us recognise sour foods and bitter which can threaten health. Plus loads of evidence for preference of sweet foods (tongue, neonates (newborns) at 3 days like it. Even cultures that don’t have sweet food such as Eskimos will start preferring it when it is introduced.

 

Although it has not been conclusively proven that the preference for sweet in humans and other animals has a strong genetic as opposed to environmental component, there is a great deal of evidence that strongly suggests that this is the case. As with the tendency to learn a preference for high-calorie foods, the preference for sweet foods would have been adaptive in the environment in which humans evolved. However, it is not adaptive now, when so many sweet foods are easily and cheaply available. The result is that we tend to over eat sweet foods, as well as other high-calorie (especially high-fat) foods. The resulting obesity and related adult-onset diabetes are an increasing problem in industrialized countries such as the United States.

The world is has a very varied climate and as humans spread from Africa to colder climates, the ability of humans to cope with different diets has been critical to our success.

 

Supports how we became so intelligent. E.g. deception, language, strategy, altruism, hunting in groups

 

Supports how gender divisions could have originated, e.g. tough testosterone stronger male versus empathy driven, caring nurturing female although in other mammals such as Bull, Lions, rams etc. the male does not hunt for flesh and the division of labour is still clear with them.

 

EP has big implications for present day modern societies. Our evolutionary heritage of food preferences and eating habits leaves us mismatched with the food environments we have created, which leads to problems such as obesity and type two diabetes (especially in individualistic societies were food is abundant) as we have a preference for high energy calorific foods (fatty, carbohydrates and sweet stuff) as they mean less time spending time foraging and yet do less activities exercise now. Plus humans have tendency to eat to excess so tide us over in times of famine or food scarcity. As the obesity epidemic has happened in the last thirty years it plausibly cannot be explained by anything else, e.g., mass low self-esteem, or genetic mutations.

An understanding of the diets of our ancestors can provide a unique perspective on our adaptations, and show how discordance between our diets and the foods we were "designed" to eat has led to many of the health problems faced by industrial societies today.

Our successful ancestors would have been the ones wired to eat as much as they could whenever they got the chance, literally not knowing when the next meal would come.  Today, we are in possession of those genes that predispose us to binge, but unlike our ancient forerunners we don’t need to go looking far for food, we don’t burn calories in our search and the next meal is guaranteed at a certain time. 

Other species that live where food is plentiful exert more self-control when it comes to food consumption.  Forzono and Logue (1992) found a positive correlation between food levels and self-control.  As food supply drops so does a species ability to exert self-control, causing them to binge.  We were “created” for a time of little so have would have benefited from little control.  Today we are not cut out for a World of plenty! 

Rather than binging in times of plenty, a better approach would be self-control.  As we grow ever more obese we are putting our health at greater risk.  As with so many human characteristics, the biology designed to preserve us is now putting us at risk. 

A01 in short for those who don’t like reading

v Darwin’s theory of natural selection states that individuals will behave in such a way as to maximize their survival and their reproductive potential.  Individuals that survive to maturity and beyond are more likely to produce offspring and be able to ensure the long term survival of their young.  In terms of evolutionary theory therefore, it pays to be healthy. 

v In present day Western society food is plentiful, but it hasn’t always been that way.  Modern examples include, the Irish potato famine when hundreds of thousands of people starved to death and millions of others were forced to flee Ireland to find food.  Stalin’s farming policy in the Soviet Union after WWII ensured the deaths from starvation of millions of Ukrainians and more recently there have been famines in Africa. Obviously famine has been part of the human condition since the EEA.

v In our not too distant past, food would often have been scarce.  Binge eating would therefore be adaptive.  It may be a while before the next meal.  As a result piling on extra pounds would have been a useful strategy for survival.  Genes that made this behaviour more likely would have made it to the next generation as their hosts (the humans with those genes) would have been more likely to survive and reproduce.  Those that didn’t binge would die out and their genes would die with them. 

v Why the preference for a high fat diet?

v Calories are essential for energy.  Every cell in the body produces energy by the process of respiration and respiration needs a constant supply of glucose.  A useful supply of sugars in times of hardship is the body’s fat reserve that can be converted to glucose.

v We seem to learn at a very young age which foods are high in calories and we develop a taste for these.  Fats are very useful for energy.  A given amount of fat contains about twice the calories of similar amounts of protein or carbohydrate. 

v In our historical past, fats would have been relatively rare.  As a result fat would have been relished and cherished!  Today, in contrast fat is everywhere, but unfortunately we have not lost that preference for it and as a result we consume it in huge and dangerous amounts.

v Eaton and Konner (1985) described what they called their ‘Paleolithic Diet’ that ancient man would have consumed.  This comprised some meat, fish, fatty oils, fruit and veg,

v Fatty foods would have provided the calories along with vitamins A and D whilst the fruit and veg would have provided a few carbohydrates and vitamins B and C.  Compared to modern diet however, carbohydrates would have been in short supply. 

v Some believe this move away from our ancient diet with a much greater reliance on Carbohydrates. Has led to increased incidence of hypertension, CHD and obesity.  Others however, such as Leonard (2002) believe that humans have evolved to be flexible eaters and as a result can live in most areas of the planet and vary what we eat. 

 

 

Please also see A02 for obesity and evolution as points there are also relevant