Download Evolutionary explanations of food preferences File

LESSON TWO – ALL YOU NEED TO KNOW
BIOLOGICAL EXPLANATIONS OF EATING
BEHAVIOUR
Specification link: You will be able to outline and evaluate:
 Evolutionary explanations of food preference
Outline and description
Material for discussion, analysis and
commentary
Our feeding system is designed to
identify the things we need and to
reject things we either do not need or
that might be dangerous such as
toxins (poisons). During evolution we
have evolved a digestive system
suited to breaking down these
foodstuffs into the nutrients we need
so they can be absorbed into the
bloodstream and metabolised by the
body.
Babies and young children show a range of taste
preferences. In some cases this is very narrow.
Our taste sensitivities are still
influenced by our evolutionary past:
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Sweet – allows us to identify
foods rich in carbohydrates
such as sugars – a key source
of energy
Sour – identifies food that has
gone off and may contain
harmful bacteria
Salt – critical to the normal
functioning of cells in the body
Bitter – associated with plant
chemicals that might be
harmful
Umami – discovered relatively
recently and represents a
meaty or savoury quality
indicating a good source of
protein.
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The ability to distinguish between
these tastes is adaptive as it is
important for survival.
There is a clear preference for sweet
foods and these supply us with
energy.
Some of their dislikes are understandable; some
vegetables such as broccoli and Brussels sprouts
contain chemicals that can be toxic to the very
young (Nesse and Williams, 1994). In adults taste
preferences settle down and stay fairly constant
with the exception of women in the early stages of
pregnancy. Morning sickness is found in at least
75% of women and has a convincing evolutionary
explanation – the embryo protection hypothesis
(Profet, 1992).
Surveys show consistently that the foods most
avoided by pregnant women are coffee, tea, meat,
alcohol, eggs and vegetables (Buss, 2008). Morning
sickness is most severe in the early weeks of
pregnancy, when the baby’s major body organs are
developing and the baby is most vulnerable. Usually
it then eases off and disappears as the baby
becomes fully formed. Alcohol and coffee and tea
(which contain caffeine) can damage the baby’s
major organs. Meat and eggs are common sources
of toxins such as bacteria, while some vegetables
contain toxic chemicals harmful to the developing
foetus. The sickness reaction therefore helps the
mother to avoid foods that may be harmful, while
vomiting prevents any toxins entering the mother’s
bloodstream and affecting her baby.
Babies can identify and distinguish between foods
from an early age. They like sweet tastes.
Furthermore, sweet foods are effective in reducing
distress in babies (Benton, 2002). This suggests an
innate (genetic) preference, possibly with adaptive
purposes.
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Food neophobia is another
evolutionary aspect of food
preferences. Neophobia means ‘fear
of the new’.
Animals have a powerful tendency to
avoid foods they have not come
across before. Although this can lead
to a dull diet, it means that we always
eat food that we know is safe and
avoid new foods that may be harmful.
An aspect of neophobia is that we
tend to show greater liking for foods
as they become more familiar.
Food preferences in babies, children and nonhuman animals are evidence for neophobia and the
evolutionary advantage of eating food we know is
safe. As we develop we learn to prefer those
flavours that are associated with high energy foods.
As Birch (1999) notes, this tendency would have
been adaptive where high energy foods were in
short supply (a common situation).
Birch (1999) notes that at the point when a young
child is just starting to eat solid foods, this
neophobia response is minimal ant his may be
because their access to food is largely controlled by
adults. However, as they become increasingly
independent (and can find food for themselves)
increasing neophobia serves a protective function.
The readiness to make quick
This can be shown in humans, but has been
associations with taste and
dramatically demonstrated in animals. Garcia,
pleasure/pain is also an evolutionary
Rusiniak and Brett (1977) made wolves sick with
advantage for us. Associative learning lamb’s meat contaminated with a mild poison
means that unpleasant side effects of wrapped in a sheep’s skin. When allowed to
eating something that does not agree approach live sheep the wolves left them alone.
with us make it unlikely that we will
They had learnt to associate the poison with sheep.
eat that food again.
Rats also show powerful taste aversion learning. If
Associative learning makes us more
poisoned at the same time as they are fed with both
inclined to avoid foods that have
a familiar and an unfamiliar food, they will in future
made us ill in the past and also leads avoid the unfamiliar food, as their previous
us to prefer flavours that have been
experience tells them that the familiar food is safe.
previously paired with a preferred
taste. There is a clear preference for
sweet foods and these supply us with
energy.
Humans are omnivores and are
The shift to meat eating helps to explain the
specialised to eat meat as well as
selective pressure on brain evolution in order to
fruits, nuts and plants. Humans
cope with new technical and social skills.
developed to eat meat about 6 million
years ago (great apes such as chimps Fossil evidence on changes to our digestive system
are usually vegetarian, but eat meat if supports hypotheses on the evolution of meat
it is available).
eating and the shift to hunter-gatherer society.
Meat is a rich source of protein and
However, there is a limited amount of fossil
evidence, and evolutionary explanations are often
this change in diet allowed the
speculative.
development of a larger brain, basic
to the success of humans.
Through evolution, other distinctive
Biological explanations of eating behaviour
eating behaviours have emerged:
especially the evolutionary approach imply that
Spices such as onions and garlic are
much of our diet is driven by nature rather than
used in cooking, especially in hot
nurture (genetics rather than environment). This
countries where food goes off quickly. ignores the cultural and social changes in food
Spices contain chemicals that kill
availability and choice over the years of human
bacteria, so protect people from
evolution. Although eating behaviour has a
poisoning.
biological and therefore ‘nature’ element’ it is also
heavily influenced by environmental ‘nurture’
factors.
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Previous exam question
June 2011
Outline and evaluate evolutionary explanations of food preference.
(4 marks + 16 marks)
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AO1 = 4 marks Outline of evolutionary explanations of food preference
There is a range of material available in this area. Candidates are likely to focus on taste
preferences (preferences for sweet, salty and umami, avoidance of sour and bitter) and their
adaptive significance.
Other approaches might include the value of moving to an omnivorous diet and the
significance of meat eating for the development for brain size and intelligence.
Examiners must be alert to unfamiliar material that is in fact relevant to the question and
creditable.
Mark scheme
AO2/AO3 = 16 marks Evaluation of evolutionary explanations of food
preference
Research studies on food preferences in babies, children and non-human animals would be
a key source of AO2/AO3 credit.
Methodological evaluation of studies may also be creditworthy, but may only earn marks
beyond rudimentary if the implications for explanations are clear.
Areas such as taste aversion learning and changes in food preference associated with e.g.
pregnancy may be popular, but again can only earn credit if discussed in the context of
evolutionary explanations of food preference.
More general commentary may include changes in food preference with age and
experience, and the possible role of associative learning, modelling and social/cultural
factors. These must be discussed in the context of evolutionary explanations to earn
AO2/AO3 marks.
Generic evaluation of evolutionary explanations would also be relevant and creditable, while
evolutionary explanations of eating disorders can earn marks if explicitly shaped towards the
issue of food preference.
Indicative issues/debates/approaches in the context of evolutionary explanations of food
preference: evolutionary/biological approaches; behavioural approach (associative learning);
social/cultural aspects; use of non-human animals in research; reductionism; free
will/determinism. Such material must be used effectively to earn AO2/AO3 credit.
AO2/AO3 material should first be placed in the appropriate band according to the
descriptors.
However, not all the criteria need be satisfied for an answer to be placed in a particular
band.
Weak performance in one area may be compensated for by strong performance in others. In
order to access the top band, issues, debates and/or approaches need to be addressed
effectively.