What is the debate?
It is questionable whether evolutionary explanations are sufficient in themselves to explain taste preferences and aversions.
Outline the role of evolution
Arguing for the sufficiency of evolutionary factors, we have evolved taste preferences for a mixed diet (including sweet foods, salt and umami) and evolved taste aversions towards bitter and sour foods. Evolutionary psychologists suggest that these preferences developed in our evolutionary history and are now genetically pre-disposed (innate) because they were naturally selective. For example sweet foods provide energy, salt is necessary for cell hydration, and umami indicated the presence of protein and saturated fat (for growth and development). Conversely, aversions to bitter and sour foods were adaptive as these flavours often indicate the presence of toxins. We also have an innate aversion to new flavours, called neophobia (as unfamiliar foods may have been harmful), which is overcome by familiarity (as it is adaptive to learn to like a flavour once we are sure that it is not harmful). Similarly, adding to the evolutionary debate, morning sickness causes mother to avoid certain foods (e.g. eggs), which is naturally selective as these foods may damage the developing baby. Finally, it is argued that we have a specialised learning mechanism (Associative Learning in Taste Aversion) that causes us to quickly learn to avoid flavours associated with illness, even after just one presentation. Therefore, by developing taste preferences, our ancestors were more likely to survive and pass on their 'selfish genes' (Dawkins), including the genetic predisposition to like or dislike these foods.
Evidence supporting sweet foods
Limited evidence to support an evolved taste preference towards sweet foods comes from Steiner, who found that Neonates show distinct facial responses to sweet foods even before any eating experiences. This suggests that an innate preference towards sweet foods, which supports a genetic predisposition for sugar as it provides us with energy to aid survival. However, this evidence can be criticised for experimenter bias, this is when the experimenter shows unintentional bias in recording and interpreting data in an effort to support their alternative hypothesis. This is due to a subjective evaluation of baby's facial expressions and at that age they do not show exact emotions as they are yet to learn them and therefore the facial expressions shown could have been negative when he interpreted them as positive.
Evidence supporting umami
Compelling evidence to support taste preferences toward umami comes from Buss, who found that meat makes up between 20-90% of the diet in all cultures and in some tribes it is acceptable for a woman to divorce a man who is not successful at hunting (the 'Sex for Meat' hypothesis). This suggests a preference towards umami which provides protein for cell growth and repair to aid survival. It also suggests that inter-sexual deselection can occur if a man is not showing signs of provision.
Evidence for aversion to sour/bitter food
Adding further weighting to the argument, strong evidence to support an evolved taste aversion towards bitter and sour foods comes from Nesse and Williams, who found that young children show taste aversions to vegetables such as broccoli and Brussels sprouts. This suggests an aversion to bitter foots for adaptive, evolutionary reasons as these vegetables can contain chemicals that can be toxic to the very young.
Why are evolutionary factors culturally absolute?
A strength of evolutionary explanations for taste preference is that they are culturally absolute because all cultures are likely to have evolved in similar ways to show the same taste aversions and preferences. This argument is convincingly supported by Buss's cross cultural research to show universal preference for meat (umami).
Are evolutionary factors considered parsimonious
For similar reasons, a further strength of evolutionary explanations for taste preference is that they are parsimonious, because they are justifiably simplistic in their explanation of eating preferences. Not only are the theories justified by research (e.g. Buss) but they are also justified by the presence of endogenous opioids, which are natural opiates produced in the pleasure centre of the mid-brain that provide feelings of euphoria when we eat sweet foods. The presence and function of endogenous opioids suggests that a preference for sweet flavours may be genetically predisposed (as suggested by the theory). Furthermore, Richard Wrangham's recent evolutionary arguments provides a justifiably simplistic explanation for our superior intelligence compare to other species, in which he suggests that the role of umami in our brain development became more significant with the advent of cooking. This is because cooked meat contains even more saturated fat than raw meat (meaning our brains developed even more than other mammals).
What is the conclusion?
However, being evolutionary, a final criticism of these theories is that they are unfalsifiable, speculative and unscientific because they are impossible to test using an I.V and D.V, as our period of evolution occurred millions of years ago. Therefore, whilst it is clear that we have preferences and aversions to certain flavours, evolutionary explanations will always ultimately be unfalsifiable.