Final answer:
A flavor enhancer is typically present at sub-threshold levels and does not impart its own flavor but enhances existing flavors. The umami taste is an evolutionary advantage because it helps identify foods rich in essential amino acids, indicating high protein content.
Step-by-step explanation:
A characteristic of a flavor enhancer is that it will be present at sub-threshold levels. Flavor enhancers, such as monosodium glutamate, are food additives that enhance the flavors already present in foods without providing their own separate flavor. These substances are based on amino acids and nucleotides and are often included in foods as sodium or calcium salts. An example of a flavor enhancer's effect is umami, which is attributed to the amino acid L-glutamate. Detecting umami can be an evolutionary advantage because it helps identify foods that are rich in essential amino acids and thus high in protein, which is vital for survival.
The ability to recognize the umami taste can be seen as an evolutionary advantage because it identifies foods that might contain essential amino acids (option c). Foods that are rich in these amino acids tend to be high in protein, which is essential for the human body. The recognition of umami enhances dietary choices by steering humans toward nutrient-rich foods which support growth and overall health.