The wild great apes derive the majority of their daily protein intake from forest plants, especially young leaves . But early hominids as well as modern humans tended to eat somewhat more digestible forms of proteins, such as meats Current Biology Vol 23 No 9 R414 Gibbons Orangutans Gorillas Chimpanzees e m i t y r a n o i t u o v E l C l o d tr o p ic a l f o r e s t d i e t

[65,66]. Umami taste is not obvious in fresh meats, but aged or cooked meats have much stronger umami taste. Consequently, chimpanzees do not appear to have a taste subsystem devoted to processing glutamate or ribonucleotides taste, although they can taste these stimuli . Hydrolyzed protein has a characteristic umami taste carried predominantly by glutamate and ribonucleotides. Humans have developed a preference for glutamate, ribonucleotides and umami taste, perhaps as markers of easily digested protein in slightly aged or cooked meats. Note that many fossil records indicate that cooking predates the origin of modern humans. In addition, humans around the world enjoy a wide range of fermented plants and animal products. Our strong interest in the taste of free amino acids and ribonucleotides may arise from an inclination to ingest fermented foods, including slightly aged and/or cooked meat. This category of food would have multiple advantages to the survival of our species.

Fermentation not only provides more ready access to macroand micronutrients, but it also provides access to probiotic bacteria, which help maintain overall nutritional health, prevent diseases, and ght gastrointestinal infections [68,69]. Although the savory taste of glutamate and ribonucleotides has been hypothesized to be a marker of protein, many high-protein foods are not particularly savory or umami tasting when fresh. It is the fermentation or aging of these foods that releases glutamate and savory taste from protein. Thus, our attraction to amino acids, especially glutamate, and savory taste may be born of a desire for fermented foods and the advantages of the improved nutrition and probiotic bacteria for our species.

The advent of agriculture eight to ten thousand years ago signicantly changed our diet by greatly increasing the role that grains and starch played. Starch, a complex glucose polymer of varying forms principally amylose and amylopectin is digested by the pancreatic enzyme alphaamylase, which breaks starch down into intermediate glucose oligomers called maltooligosaccharides (MOS) and isomaltooligosaccharides (IMOS). These in turn are further cleaved into maltose (a glucose disaccharide). Maltase ultimately cleaves maltose into glucose, which then passes into the blood. All mammals produce pancreatic alphaamylase. But a few mammals, great apes and some rodents (rats, mice, voles), also produce commensal a rly h m i n i d x D i e t a r y e y fr o a w a i n t o s o y e b a Humans si o m f o r e n a n n