EVOLUTIONARY EXPLANATIONS OF FOOD PREFERENCE

Taste receptors are located on the tongue. Saliva breaks down our food into basic molecules which are combined with the taste receptor sites. This combination then triggers activity in the gustatory nerve, which transmits taste information to the brain.

It used to be thought that these receptors were in specific places on the tongue, resulting in a 'tongue map'. However, now it is very clear that the receptors are all over the tongue. 

Another debate centres on how many different tastes we ca sense. It used to be thought that it was only bitter, sweet, salt and sour but most scientists now agree there is a fifth taste called umami, identified by a Japaneese scientist called Kikunae Ikedain in the early 1900s. This taste is most common in Japanese foods, particularly kombu, a type of sea vegetable similar to sea kelp; it's also in bacon and MSG.

There's also a debate about a sixth receptor for fat.

Why would taste receptors be important?

• Sweet - energy - rich in carbohydrates.
• Sour - identify food that's off and may contain bacteria.
• Salt - critical for normal cell functioning.
• Bitter - dangerous plants.
• Umami - meaty/saboury flavour - protein.

There is research that shows the bitter tase has evolved as a defence mechanism to detect potentially harmful toxins.

Sandell & Breslin screened 35 adults for the TAS2R bitter tast receptor gene. Pts rate the bitterness of various vegetables, some of which contained glucosinates and others did not. Glucosinates are well known for their toxic effects in high doses. Those with the sensitive form of the gene rated the glucosinate containing vegetables as 60% more bitter than those with the insensitive form of the gene.

How did we become hunters as well as gatherers?

Meat is a good source of protein and high in calories and fat - much more so than vegetables. One theory looks at the advantage to humans in having an excess of protein - perhaps the extra protein was needed to develop the extra brain functions.

Also, hunting itself meant that people would progressively get more intelligent, the occasionall kill, whilst more difficult to achieve, allowed humans to spend less overall time finding food and more time eating. The time saved could therefore be used for more productive things, like inventing.

As humans invented more things (tools/weapons etc.), more time was saved. They became super-efficient hunter-gatherers. Hunting also encouraged group participation, social co-operation, navigation etc - this then made 'higher order' skills, like language, a distinct evolutionary advantage.

Over time, larger brains also to cope with these new skills would develop and these, in turn, would require more protein to keep them runnning effectively.

• For out ancestors in the environment of evolutionary adaptation, meat was also an important source of saturated fat. Fat was vital for survival, yet not readily available in early human environments.
• Anthropologist Craig Stanford's observations of chimps in a nature part, shows that these animals face the same problems today as our ancestors did millions…