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Eating Behaviour Unit PSYA3 Miss Bird
What will we cover in this topic? Where we are now What we have covered
The goal of any evolutionary explanation is to discover the adaptive function of a particular behaviour i.e. what is the purpose of that particular behaviour? The mechanisms that make up human nature were designed by natural selection millions of years ago. Therefore we need to consider the problems faced by our distant ancestors to discover why behaviours, such as food preferences, evolved in the first place. Evolutionary explanations of food preference
Individuals will behave in such a way as to maximize their survival and their reproductive potential. Individuals that survive maturity are more likely to produce offspring and be able to ensure the long-term survival of their young. Therefore, in terms of evolutionary theory, it pays to be healthy in terms of what we eat in order to survive and pass on our genes to our offspring. Darwin: Natural selection
The environment of evolutionary adaptation (EEA) • Early diets were dependent on the environment that humans found themselves in. • Preferences for fatty/high calorie food would have been adaptive for early humans as a source of energy. • Conditions in the EEA at this time meant that energy resources were not only vital to stay alive but were needed to provide the human with enough energy to find their next meal. The evolution of food preferences
Unlikely that humans would get enough nutrients from a vegetative diet alone. • Therefore began to include meat in their diets. • Evidence from fossils suggests that their daily diet consisted primarily of animal-based foods, in particular organs, which are a rich source of energy. Continued…
A meat diet full of densely packed nutrients provided the catalyst for the growth of the brain. • Meat supplied early humans with all the essential amino acids, minerals and nutrients they required, allowing them to supplement their diet with plant-based food that have few nutrients but lots of calories for energy (e.g. wheat). Continued…
Our modern preferences for calorie-rich/fatty food can therefore be traced back to the adaptive problems faced by our ancestors. I.e. we prefer foods that are high in calories so that we can supply our brains and bodies with the energy that we need to survive and reproduce. To summarise…
Read the study by Gibson and Wardle (2001) and answer the questions in your booklet. You have 10 minutes. Independent task
Who can identify some different tastes? • Sweet – identify foods rich in carbs 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. What do we like (and not like)?
There is evidence that we are born with genetic predispositions for basic tastes and that these influence our food preferences. • One suggestion is that we are predisposed to prefer sweet and salty foods and to reject bitter and sour foods. • Support comes from neophobia in young children Are we predisposed to food preferences?
Neophobic infants are more likely to reject new foods in favour of those that are already familiar to them. • This suggests that we are predisposed to be conservative in our food preferences (stick with what we know is safe). What is neophobia?
We have an innate preference for sweet things (Rozin, 1982). Why? • Sweetness indicates the presence of sugar which in turn indicates calories needed for energy. • Evidence from human biology that we are sensitive to sugar. • The nerve that runs from our tongue to our brain carries more fibres that are sensitive to sweetness than any other flavour sensation (i.e. bitterness, sourness or saltiness). Why do we like chocolate?
Desor et al (1973) • Investigated babies food preferences based on facial expressions and sucking behaviour. • New-born babies (only 1-3 days old) demonstrated innate preference for sweet-tasting food. • Rejected bitter tasting substances. Support for innate sweet preference
These taste receptors help us to identify food that has gone off. • Leads to the facial expression of ‘disgust.’ • This natural reaction is seen in human infants and other primates. • Suggests innate. • This feeling leads to avoidance of bitter and sour tasting foods. Why don’t we like bitter and sour?
Meiselman et al (1989) – all cultures seem to prefer sweet tastes to any other suggesting innate preference. Bell et al (1973)– Eskimos in Alaska lack sweet foods in their diet. However they are quick to accept sweet foods into their diets when they come into contact with them, even though they have no experience of them. Supports the idea of an underlying human preference for sweet foods. Research
“We are predisposed to learning preferences by associating foods with the context and consequences of eating them.” (Birch, 1999). • More inclined to avoid foods that made us ill in the past. • Prefer flavours that have been previously paired with a preferred sweet taste or with nutrients that supply us with energy e.g. sugar. These predispositions are highly adaptive as they reduce the likelihood that young children will eat harmful substances (often indicated by sour or bitter tastes), therefore increasing the probability of their survival. Associative learning
First found by farmers trying to rid themselves of rats. • Difficult to kill rats using poisoned bait as they would only take a small amount of any new food, and if they became ill, would rapidly learn to avoid it. • Learnt to associate taste of certain food with symptoms (e.g. vomiting) caused by poisonous substance, therefore developed an aversion to it and would avoid it in the future. Taste aversion
Garcia et al (1955) – first to study taste aversion in lab Rats were given saccharin- flavoured water and shortly after were exposed to radiation(which made them feel ill e.g. nausea). When given the saccharin-flavoured water again, they avoided it. Therefore had developed an aversion to saccharin as they now associated it with illness. Taste aversion
The development of taste aversions would have helped our ancestors to survive because, if they were lucky enough to survive eating poisoned food, they would not make the same mistake again. Such aversions are very hard to shift – an adaptive quality designed for survival. How might smell/taste aversion play a role in morning sickness? Often results in avoidance of particular foods from taste/smell associated with nausea/vomit Evaluation of taste aversion
Could early humans have been vegetarian? Cordain et al (2006) Argued that early humans consumed most of their calories from sources other than saturated animal fats i.e. plant-based foods. This has led to the suggestion that our distant ancestors were healthy eaters and may even have been vegetarian. However, evidence shows that all societies display a preference for animal foods and fats (Abrams, 1987). Also, if early humans were completely vegetarian would they have been able to get sufficient calories from plants and grains in order to survive? Evaluation
It has been argued that not all food preferences are a product of evolution. A trait that is beneficial today (e.g. consumption of low cholesterol foods) would not have evolved because of its beneficial effects for our ancestors. Our ancestors viewed saturated animal fats as important for energy (and survival!) whereas today we view them as harmful and try to avoid them in order to survive and stay healthy. Evaluation
Cultural differences: Innate responses do not account for the broad range of food likes and dislikes that develop beyond infancy. Evolved factors important in food selection but these are modified by our experience with different foods in our culture. Real-world applications: Research on taste aversion has been helpful in understanding the food avoidance that can sometimes occur during the treatment of cancer. Some cancer treatments can cause gastrointestinal illness. When this illness is paired with food consumption, taste aversions can result. Evaluation: IDA
In pairs, apply relevant IDA to the evolutionary explanations of food preference. Write your ideas down in the box on your worksheet. Methodological issues Ethical issues Reductionism Nature vs. Nurture Pair task: IDA
For each term or name in the table, colour code whether it is linked to neural mechanisms in eating behaviour or evolutionary explanations of food preference. Plenary (K&U)
Quiz. • Brief run through of evolutionary explanations for eating behaviour as a class. • Test (24 marks) – on all of topic so far. Next lesson…