1. Learning Objectives
To briefly revise the neural mechanisms for controlling satiation and hunger
To outline research into the evolutionary explanations of food preference.

2. Recap - what do the following words mean?
Ghrelin
Insulin
Glucagon
VMH LH
CCK

3. Ghrelin Hormone released from the stomach.
The less food in the stomach - the higher the level of ghrelin released
Gastric bands lower levels of ghrelin
It works directly on the hypothalamus and ‘switches on’ feeding behaviour.

4. Insulin Released from the pancreas
Enables the body to convert glucose in the blood to glycogen for storage.
The pancreas may become unable to release either enough insulin or become damaged. These problems will lead to diabetes.

5. Glucagon
This is the hormone released from the pancreas that will turn stored glycogen back to glucose.
The glucose is then released into the blood for use.

6. VMH Ventro-Medial Hypothalamus.
This area of the brain inhibits feeding.
Research in rats quite conclusive.
If the rat’s VMH is damaged you will end up with obese rats – the ‘stop’ signal no longer works

7. LH - ‘GO GO GO’
An area of the hypothalamus called the Lateral Hypothalamus.
This area stimulates feeding.
Research on rats confirmed that if the LH is damaged the rat stops eating (aphagia) as the ‘on switch’ no longer works

8. CCK – STOP! Cholecystokinin is a hormone released from the duodenum.
It is released once the food has passed from the stomach to the small intestine.
It acts on the hypothalamus as a satiety signal when there is food present.

9. Review: neural explanations for eating & satiation

10. Hunger, Eating and Satiation: the process
Increase in blood glucose
Ventromedial hypothalamus activated
Satiety
reached
Hunger develops
Lateral hypothalamus activated
Blood glucose levels drop
Eating stops

11. Evolutionary explanations for food preferences
Next…
Evolutionary explanations for food preferences 11

12. 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) era
Natural selection favoured
adaptations geared
towards survival

13. The EEA EEA=environment of evolutionary adaptation.
This is the environment our ancestors lived and evolved in.
We evolved from the African savannah some 2 million years ago.
We survived because of our ability to adapt to our environment.
Our ancestors passed these adaptive genes to us, hence the reason the human species survived.

14. Evolutionary explanations of food preferences
Evolutionary theory suggests that organisms should behave so as to maximise survival and successfully reproduce to pass on their genes (Barash, 1977).
Survival depends on number of things, one of which involves remaining healthy by managing to obtain sufficient nutrients to meet demands of the body 14

15. Why do we eat some foods but not others?

16. FOOD PREFERENCES
Nature Nurture

17. Preference for high-calorie food
It was adaptive for humans to learn which foods have high nutritional value (high-calorie), since calories are essential to provide energy for the body to function
Those humans who learnt quickest which foods would provide the most nutrition were the most likely to survive and reproduce. 17
Evolutionary explanations

18. Early diets
Originally hunters and gatherers who ate animals and plants.
We had a preference for fatty foods because fat was a vital energy resource for survival
This is the reason why we still prefer high calorie foods, although it isn’t necessary for our life styles nor our survival.

19. Problems with studying this area
Have to rely on fossil evidence.
Also have to look at primates and extrapolate evidence.
Cannot use conventional scientific methodology.
Can observe living hunter-gatherer societies/tribes.
Food shopping behaviour shows gender differences!!

20. Testing evolutionary explanations for food preferences
We can’t go back in time to see for sure how our ancestors ate.
So we compare preferences with those of monkeys who face similar adaptive problems today that we did 2 million years ago.
Craig Stanford observed Chimps in an African national park:
Chimps had similar problems to us 2 million years ago in that meat is also scarce and where they’re starved for meat.
Therefore when they do manage a kill, they go straight for the fattiest part: The brain and bone marrow rather than nutritious flesh.

21. What is gustation? This is our sense of taste.
Which tastes can humans detect?
We can detect sweet, sour, salt and bitter tastes.
Recently we have discovered that Umami is a taste quality of food that we can detect - it is a meat or savoury taste. (good source of protein foods)

22. Lesson 2: Taste Aversion
Why are these little cuties pulling faces?
Why survival benefit does disliking sour tastes confer?
What survival benefit does disliking bitter tastes confer?
Sour suggests food is off, i.e. milk, meat etc. Play BBC Horizon: The truth about taste from 10 minutes to 14 mins.

23. 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

24. Preference for sweet foods
A sweet taste is often associated with ripeness, a high concentration of sugar and a quick fix of calories
A preference for sweet food/drinks that would encourage consumption of ripe fruit was probably advantageous to our early ancestors (Rozin, 1982) 24
Evolutionary explanations

25. Preference for salty foods
Salt is essential for the body to function properly
Infants about four months old seem to show a marked preference for salty foods over non-salty
At the age of two years, children reject foods that do not contain the expected amount of saltiness (Beauchamp, 1987) 25
Evolutionary explanations

26. Sweet food = fruit = natural fructose content = energy
Bitter = poison
Neophobia = fear of new foods (unknown =>possibly dangerous)

27. Davis (1928,1939) observed choices of children living in a paediatric unit
Found that young children had an innate , regulatory mechanism and make healthy food choices
BUT they could only do so if healthy food was actually available!!!
So food choice changed over time based on the environment

28. Why don’t we like bitter and sour?
These receptor help us 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

29. Evidence supporting evolution of bitter taste aversion
Sandell and Breslin (2006) screened 35 adults for the hTAS2R38 bitter taste receptor gene. The participants were given a diet that contained vegetables with Glucosinolates. Glucosinilates, are found in broccoli and Brussels sprouts and when taken at really high doses can be toxic. Glucosinolate also gives these vegetables their bitter taste.
Participants with the sensitive form of the gene found the vegetable 60% more bitter then the insensitive form of the gene.
They can say just a specific gene that codes for a bitter taste receptor.

30. Bait Shyness : Association
Bait Shyness: Rats given poison were not being killed as they only took a small amount, got ill and then associated the illness with the bait.
Garcia (1955) gave saccharin to rats just before exposing them to radiation. They found after exposure the rats developed an aversion to saccharin.

31. Adaptive Advantage of Taste Aversion
Taste and odour can be linked to taste aversion.
The association can occur up to 24 hours after the consumption of food. If you ever got food poisoning from a restaurant, would you go back?
Why would this be advantageous to our ancestors?

32. Taste aversion: Why we prefer certain tastes to others.
Humans learnt that certain foods are better for health.
They therefore chose nutrient rich food and developed an aversion for foods that didn’t enhance their chances for survival.
This was confirmed in lab tests on rats. Farmers for example found that when they tried to poison rats, it wasn’t useful as they would only eat small amounts of poison, which would make them sick. They would therefore associate ill health with the poison and therefore developed an aversion for it.
Detecting toxins: Our bitter taste evolved as a way to detect poisons in plants = ensure survival.

33. Commentary on taste aversion
Seligman supported the idea that we avoided certain types of food because they didn’t enhance our chances of survival. He called this “biological preparedness”.
This was supported by research on cancer patients undergoing chemo and radio therapy (Bernstein & Webster)
When gave novel tasting ice cream prior to treatment, people developed an aversion to it.
The body associates that taste with illness and therefore creates an aversion so that it isn’t eaten again.

34. Medicine effect
If we associate a food with recovering from an illness we may have preference for that food.
Garcia et. al (1955) Rats who were given a distinctive flavour when given thiamine injections developed a preference for that
flavour.
Thaimine is an amino acid also known as vitamin B1. Helps convert carbohydrates to energy, so would perk the rats up!

35. Commentary: Supporting & opposing diet preferences
Gibson & Wardle confirmed the idea that our ancestors preferred calorie rich food.
In their research, they allowed children to choose fruit and veg.
Findings: Children chose potatoes & bananas which are very high in calories. This isn’t because they were sweet or nutritious, but because they had the most calories.
Cordain et al: Suggested the perhaps our ancestors were vegetarian as originally we consumed most of our calories from non-animal resources.
Abrams the anthropologist opposed this and said that evidence shows that all societies show a preference for animal foods and fats. Also, grains and plants available wouldn’t have been sufficient for our ancestors to survive from.

36. Morning Sickness
This is thought to be an evolutionary hang-over. It is thought that it developed to protect the early stages of foetal development (when all the organs were forming). It stopped potentially dangerous toxins from being ingested by the mother to be.
Caffeine is one thing that pregnant women can stop liking in the early stages.
Now with nutritional information and excellent healthcare (in UK) morning sickness is not useful!!

37. Preference for meat
Quality of plant foods declined (due to receding forests 2 mill years ago) = preference for meat
Fossil evidence: Ancestors ate mostly animal organs such a liver, kidneys & brain (extremely rich in nutrients).
This helped our brains to evolve according to our need to adapt to the environment.
Without meat, we wouldn’t have been able to grow our brains and therefore adapt to our environment and survive until today (Milton 2008)

38. We cannot look at this from just a biological viewpoint.
Cultural transmission of food preferences is very important.

39. Then technically, we should all have the same food preferences, no?
Yes, that’s true:
We know that all children love sweet foods and most of us have to control the amount of fatty foods we eat in order to maintain health
But culture and food experiences also play a part.
However, our innate preferences are universal, they are just refined by our experiences.

40. Avoidance of food poisoning
Cultural transmission of the use of spices is very important. Onion and garlic are excellent at killing bacteria in food.
We know what food smells/tastes like when it has gone off (detected by our sour and bitter taste buds).
We are also taught which foods are good/bad for us.
Food neophobia - fear of new food. Stops us eating anything dodgey!!

41. Summary:
A sweet taste is often associated with ripeness, a high concentration of sugar and a quick fix of calories
A preference for sweet food/drinks that would encourage consumption of ripe fruit was probably advantageous to our early ancestors (Rozin, 1982)
Salt is essential for the body to function properly and Infants about four months old seem to show a marked preference for salty foods over non-salty
At the age of two years, children reject foods that do not contain the expected amount of saltiness (Beauchamp, 1987)
Newborn babies demonstrate innate preference for sweet tasting food
Babies reject bitter tasting substances
Sweet food = fruit = natural fructose content = energy
Bitter = poison

42. Evaluation
Strengths
Weaknesses
gives an explanation that can account for both nature and nurture
Reductionist and determinist (eating is caused by events happened years ago)
can explain innate food preferences
difficult to falsify, so questionable validity
focus on ultimate rather than proximate causes could provide more effective intervention strategies
has human evolution stopped or are we still adapting?
Discuss two or more evolutionary explanations of food preference (24 marks)