Download Eating Behaviour 4 – Evolutionary explanations of food preference

Eating Behaviour
PSYA3
Miss Bird
AQA A Specification
Factors influencing attitudes to food and eating behaviour. For example:
Eating behaviour cultural influences; psychological influences (mood); and social
influences (health concerns/media).
Explanations for the success and failure of dieting.
Neural mechanisms involved in controlling eating behaviour.
Biological
explanations of Evolutionary explanations of food preference.
eating behaviour
In relation to either anorexia nervosa or bulimia nervosa:
Eating disorders
Psychological explanations.
Biological explanations, including neural and evolutionary explanations.
Evolutionary explanations of food
preference
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
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 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.
The evolution of food
preferences (A01)
The environment of evolutionary adaptation (EEA)
 Early diets were dependent on the environment that
humans found themselves in.
 Early humans had a vegetative diet.
 However it is unlikely that they would get enough
nutrients from a vegetative diet alone.
 Therefore our human ancestors began to include meat in
their diets.
 Consequently our preferences for fatty food today (e.g.
meat) would have been adaptive for early humans as a
source of energy.
 They would need this energy (from fatty food) in order to
survive and to hunt for their next meal.
The evolution of food preferences
continued… (A01)
 Evidence from fossils suggests that our ancestors
daily diet consisted primarily of animal-based foods,
in particular organs, which are a rich source of
energy.
 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 plantbased food that have few nutrients but lots of
calories for energy (e.g. wheat).
A01: To summarise…
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.
Independent task (A02)
Read the study by Gibson and Wardle (2001)
and answer the questions in your booklet.
You have 10 minutes.
Gibson and Wardle (2001) provided evidence to support the
importance of calories in an ancestral diet. They showed that the
best way to predict which fruit and vegetables would be preferred by
four-to-five year old children was not in terms of sweetness, protein
content or familiarity, but in fact calorie content. Bananas and
potatoes (which are particularly calorie-rich) were more likely to be
chosen by the children, therefore demonstrating an evolved
preference for calorie-rich foods.
1.4-5 years old
2.Sweetness, protein content, familiarity and calorie content.
3.Children more likely to choose calorie-rich options.
4.Needed for energy in order to survive and reproduce.
5.This research supports the idea that there is an evolved
preference for calorie-rich foods that are essential for survival.
P.E.E.L (A02)
• P: There is research evidence to support the evolutionary
explanation of food preference, particularly for calorierich/fatty foods.
• E: Research by _____________ has shown...
• E: This suggests/shows...
• L: This supporting research evidence by _____________
suggests that the evolutionary explanation is a valid
explanation of food preference.
Pair taste test (OPTIONAL)
One of you will be the participant and the other will be the
experimenter.
The participant will be blind-folded and will take part in a taste
preference test. You will try 4 different food substances, and between
each food you will have a drink to cleanse your pallet.
The experimenter will provide the participant with the 4 different foods
and record the ratings/facial expression for each taste on A4 paper.
You will use a rating scale of 1-10 with 1 being ‘absolutely disgusting’
and 10 being ‘absolutely amazing’.
You have 10 minutes!
What do we like (and not
like)?
Who can identify some different tastes from the taste test?
1. Sweet – identify foods rich in carbs to provide us with
energy.
2. Sour – associated with food that has gone off and therefore
should be avoided.
3. Salt – critical for functioning of the cells and therefore need
to identify.
4. Bitter – associated with poisonous plants, should be
avoided.
A01: Predisposed to food preferences?
• There is evidence that we are born with innate 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
What is neophobia?
Unwilling / reluctant to try new foods.
• 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.
A01: Why do we like chocolate?
 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).
A02: Support for innate sweet preference
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.
• Why were newborn babies studied?
Why don’t we like bitter and
sour?
• These taste receptors help us to identify food that
has gone off.
• Leads to the facial expression of ‘disgust.’
• This is seen in human infants and other primates.
• Suggests innate.
• This feeling leads to avoidance of bitter and sour
tasting foods.
A02: Supporting research
evidence
Meiselman et al (1989) – all cultures seem to prefer sweet
tastes to any other suggesting inherited food 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
innate preference for sweet foods.
P.E.E.L (A02)
• P: There is research evidence to support the evolutionary
explanation of food preference, particularly for sweet
tastes.
• E: Research by _____________ has shown...
• E: This suggests/shows...
• L: This supporting research evidence by _____________
suggests that the evolutionary explanation is a valid
explanation of food preference.
A01: Associative learning
“We are predisposed to learning food preferences by associating
foods with the context and consequences of eating them.” (Birch,
1999).
1)More inclined to avoid foods that made us ill in the past.
2)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.
A01: What is taste aversion?
• LEARN TO AVOID CERTAIN TASTES TO ENSURE SURVIVAL.
• 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.
A02: Supporting evidence for
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.
 Suggests that they had learned to avoid certain tastes to ensure
survival supporting evolutionary explanation of eating behaviour.
A02: Evaluation of 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.
A02: Evaluation
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 today 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?
A02: 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.
Indicates a change in food preferences over the years.
A02: IDA
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.
Pair task: IDA
In pairs, apply relevant IDA to the evolutionary
explanations of food preference.
Write your ideas down in the box on your worksheet.
You have 5 minutes.
IDA
Methodological – studies in laboratory – controlled observations but
may lack ecological validity.
Ethical – research on taste aversion in rats – distressing? Can findings
be generalised?
Deterministic – food preferences due to evolutionary factors, ignores
social, cultural, psychological and cognitive influences.
Nature vs. Nurture – suggests food preferences are strongly
influenced by genetic factors passed down through the ages and
heavy emphasis on innate food preferences from ancestors to aid
survival.
Plenary: Consolidation
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.
You have 5 minutes.
Q&A on key terms.
Homework 
1. Complete the essay structure and gap-fill
IDA paragraph in your booklets.
2. Revision aid on evolutionary explanations
of food preference.