1. Evolutionary Explanations for Eating Behaviours

3. How might certain behaviours have been adaptive in the past?
Back in the Environment of Evolutionary Adaptiveness, in hunter-gatherer societies, it may have been better for certain tastes for food to have developed in humans. Such tastes may have been functional in some way in the past and have resulted in for example fewer deaths and the furtherance of the human race!

4. Key Terms
The EEA – The environment of evolutionary adaptiveness – this refers to the environment in which a species first evolved. Human beings first emerged as a separate species 2 million years ago in the African Savannah.
Natural selection – the process by which inherited traits that enhance an animal’s reproductive success and ability to survive are passed on to the next generation and thus are selected.
Natural selection favoured adaptations geared towards the African Savannah.

5. 3 groups using your text book, how can we explain the following?
Preference for fatty foods (Early Diets)
Preference for meat – How did this help human beings to evolve?
Taste aversion learning – we quickly learn to avoid anything that makes us sick.

6. Early diets
Human beings were hunter gatherers whose diets included the animals and plants that were part of their natural environment.
Preferences for fatty foods would have been adaptive for early humans, because conditions in the EEA meant that energy resources were vital in order to stay alive and to find the next meal.
Although modern humans are more concerned with nutritional value of food, instead what we actually eat is often rich in calories and not that nutritious. In the EEA it would have been more difficult to find calories, which explains why we are now hardwired to enjoy them!

7. Preference for Meat
Human beings began to include meat in their diets to compensate for a decline in the quality of plant foods caused by receding forests two million years ago.
Fossil evidence from groups of hunter-gatherers suggests that their daily diet was derived primarily from animal based foods, often organs such as liver, kidneys, brains – rich sources of energy.
According to Milton (2008) a meat diet full of nutrients, amino acids and minerals provided the catalyst for the growth of the brain.
It is likely that had they remained vegetarian they would not have evolved into intelligent creatures.

8. Taste Aversion
Bait shyness or taste aversion develops very quickly through classical conditioning – it was discovered that rats will learn very quickly not to eat bait since it makes them ill.
The development of taste aversions would have helped our ancestors to survive because if they were lucky enough to survive eating some poisoned food they would not make that mistake again.
Taste aversions can still be acquired up to 24 hours after eating a food as reaction to poison food is often delayed. Once learned such aversions are hard to shift.
Generally, a natural avoidance of bitter foods (often found in babies) is adaptive as this helped our ancestors to avoid foods that may be poisonous.

9. Embryo protection hypothesis
Morning sickness has evolved to help the mother avoid foods that may harm the growing foetus.
Foods that are avoided : coffee, tea, alcohol, veg, meat and eggs.
Many of these foods contain toxins that are harmful to the baby.

10. Real-world applications
Understanding the adaptive origins of taste aversion has been helpful in understanding the food avoidance that sometimes occurs in cancer treatment.
Chemotherapy and radiation can cause gastrointestinal upsets. When this is paired with food consumption, taste aversions can occur.
Webster (1980) gave patients a novel-tasting ice cream prior to their chemotherapy and the patients acquired an aversion to that ice cream. These findings have led to the scapegoat technique where cancer patients are given a novel food along with a familiar food prior to chemo. The patient forms an aversion to the novel food (which doesn’t matter) and not to the familiar food. This is consistent with our general adaptive avoidance of novel foods – neophobia.

11. AO2 Using your book write down one AO2 point for each of
Early diets – fat and carbs
Preference for meat
Taste aversion
Develop two IDA points related to Evolutionary Explanations of food preferences.

12. Preference for high calories
There is some evidence that human beings may be hardwired to enjoy high calorie foods.
Gibson and Wardle – The best way to predict which fruit and veg will be preferred by 4-5 yr olds is by how dense they are in calories. Bananas and potatoes were more likely to be chosen by children, demonstrating an evolved preference for calorie rich food.

13. We can test the evolutionary hypothesis through comparisons with related species such as chimpanzees who might face similar problems today. Stanford has observed chimps in Tanzania and notes that (as for our ancestors in the EEA) fat is vital for survival. These chimps face the same problems our ancestors did millions of years ago. When they do manage a kill they go straight for the fattiest parts – brain and bone marrow rather than nutritious flesh. We can perhaps relate these observations to our modern day preferences for fatty food.

14. Anthropological evidence indeed shows that all societies display a preference for animal foods and fats. It would not have been possible in fact for early humans to be vegetarian as they would not have been able to gain sufficient calories from the plants and grains available.

15. The evolutionary explanation of our food preferences is reductionist because…
The evolutionary explanation of our food preferences is determinist because it suggests we like certain foods because of evolutionary hard-wiring and have no free will. A problem with this is that it takes away our responsibility for eating healthily and suggests there is nothing we can do for example about obesity. It legitimates unhealthy eating patterns.

16. The explanation is reductionist because it simplifies what may be a complex set of reasons for our eating choices down to one thing. In fact there may be many proximate explanations for the human desire for fat and sugar – not least advertising, modern life styles and so on.
The evo explanation is an ultimate explanation and in fact this could however be useful in terms of developing therapies based on an acceptance that we are all attracted to fatty/sweet foods.

17. An ultimate explanation
Explaining our modern day food preferences for burgers and chips in terms of evolutionary hard-wiring back in the EEA is of course an ultimate explanation. In fact an ultimate explanation such as this could lead to more valid ways of treating obesity for example.
However, the explanation is reductionist because it simplifies what may be a complex set of reasons for our choices down to one thing. In fact there may be many proximate explanations for the human desire for fat and sugar – not least advertising, modern life styles and so on.

18. The vast majority of food preferences in fact appear not to be predetermined. The evolutionary explanation cannot very satisfactorily explain the cultural differences in food for example. However the strong desire for fatty and sweet food that children show and the general worldwide preference for fatty and salty food appear to be universal. Evolved factors in food selection are clearly important but these are modified by our experience with different food, with culture determining our experience.

19. Taste aversion has been explained by Seligman as part of biological preparedness. Different species he said, evolved different learning abilities. This natural selection of differential learning has occurred so that each species has the ability to learn certain associations more easily than others, particularly those associations that help individuals survive.

20. Scientists have long assumed that bitter taste evolved as a defence mechanism to detect potentially harmful toxins in plants. An American study provides the first direct evidence in support of this hypothesis.
Sandell and Breslin (2006) screened 35 adults for a bitter taste receptor gene. Pps rated the bitterness of various veg, some of which contained glucosinolates and others that did not. Glucosinates are well known for their toxic effects at high doses. Those with the sensitive form of the gene rated the glucosinolate containing veg as 60 per cent more bitter than those with the insensitive form of the gene. The ability to detect and avoid naturally occurring glucosinolates would confer a selective advantage to our ancestors which explains why such genes are widespread today.

21. And a couple of other points…
An evolutionary account of food preferences is of course determinist as it overlooks the fact that human eating behaviour is also controlled by thoughts and emotions – we have free will.
Evolutionary concepts such as adaptiveness can be applied to many behaviours, eating, sexuality, aggression, relationships. However we cannot prove or disprove empirically that our eating behaviour is an evolutionary adaptation. Evolutionary theory of eating cannot be falsified.