Taste of bitter compounds and dietary choice influences Man's life
advantageous" in human evolution, report European researchers.
Animals rely on chemical perception, including the senses of taste and smell, for protection against the harmful compounds found in nature.
It is widely believed that behavioral and dietary choices may have reduced the importance of such chemical perception in higher primates, and particularly in humans.
The human tongue has about 10,000 taste buds with five taste sensations: sweet, bitter, and umami, which work with a signal through a G-protein coupled receptor; salty and sour which work with ion channels.
Contrary to popular understanding, taste is not experienced on different parts of the tongue. Though there are small differences in sensation, which can be measured with highly specific instruments, all taste buds, essentially clusters of 50 to 100 cells, can respond to all types of taste.
Taste buds (or lingual papillae) are small structures on the upper surface of the tongue that provide information about the taste of food being eaten.
Researchers Nicole Soranzo of University College London and Bernd Bufe at the German Institute of Human Nutrition investigated the potential role natural selection played in forming present sensitivities and protecting Man from harmful natural chemicals.
The team analysed the nucleotide sequence of a human gene encoding a bitter-taste receptor that mediates recognition of a class of naturally ubiquitous, but toxic, cyanide-releasing compounds.
By analysing sequences from a large sample of individuals representing 60 human populations, researchers found evidence that specific variants of the receptor gene have been strongly favoured in the early stages of human evolution.
They showed that variants of the receptor, when expressed in individual cells, conferred an increased sensitivity toward several harmful compounds found in nature.
"The work strongly supports a pivotal role for bitter-taste perception in toxin avoidance in humans, an attribute that could have come into particular play during periods of expansion into new environments," the researchers report.
More broadly, the work contributes to the debate on the mechanisms governing the evolution of chemical sensory perception and on the role of diet as a selective force in human evolution.
Full findings are published in Current Biology, Vol. 15, pages 1257-1265, July 26, 2005. DOI 10.1016/j.cub.2005.06.042.
