**4. Starting at the beginning: human evolution and food intake**

The need of water and food was stated as a key necessity in the Maslow Hierarchy of Needs [122]. As humanoids evolved, the feeding techniques and the human chewing capabilities have evolved and adapted through time. Paleoanthropologist Dr. Rick Potts is the founder of the Human Origins Program at the Smithsonian's National Museum of Natural History, Washington, DC [123]. Potts describes the evolution of the human cranium developing from a small brain case and slope-like face to our current species with the largest brain case and the smallest face. The mandibular bone (not shown on the video) would have also changed in shape and strength affecting the capacity to chew foods and prepare the food bolus for swallowing.

Ledogar and colleagues [124] studied the morphology and the facial biomechanics of cranium specimens from various regions around the globe. Using computational biology, the research group created a model (named ALL-HUM) incorporating several characteristics of crania to which they allocated human bone tissue and masticatory muscle force values in order to predict cranial mechanics and calculate strains and bites forces of our ancestors. The masticatory gracilization over time of the human face was less stiff than the chimpanzee comparatives but were efficient in bite force application. These findings support the hypothesis that consumption of less mechanically challenging foods or the origination of extraoral processing techniques (tools and cooking) accompanied these morphological changes. Humans adapted in several ways to evolved in various regions of the globe. One impressive adaptation was food preparation as well as feeding and chewing techniques as it is essential to survival of the species.

#### **4.1 Taste perception**

The biomechanics of human masticatory abilities are definitely important elements of feeding. However, feeding evolution is not only linked to our capacity to mechanically break down or process foods. It is associated to an array of sensations which also guide humans in accepting or refusing the ingestion of substances. It is believed that taste perception is an adaptive response [125] to assessing nutritional content or toxicity of foods. Initially believed to be spatially mapped on the tongue, it is now understood that taste receptors are found across the tongue [126]. In fact, located in the oropharyngeal region, the primary tastes of sweet, bitter, salty, sour and umami receptors could have helped humans in detecting acceptable foods sources. One type of taste receptor cell was identified for each of the sweet and umami tastes. For salt and sour tastes, possibly more than one are involved. However, bitter taste is detected by 25 different types of cell receptors [127, 128]. Therefore, primates and humans are capable to detect bitterness which prevents the consumption of possible toxic plants [129]. Animal studies have shown that, although specific taste buds regenerated at a high turnover rate, they maintain the capacity to reconnect to the central nervous system due to labeled line wiring. Essentially, labeled line wiring allows the bitter taste center to convey and perceive only bitter peripheral signal or the sweet center carry only sweet signal. The molecules responsible for directing these gustatory nerves are known as semaphorins and are proteins involved in neuronal axon guidance which permit high specificity [130–133]. Consequently in humans, taste perception is highly regulated and neurologically wired to allow innocuous ingestion of a wide array of substances.

New investigations pertaining to the microbiome have associated oral microbiota composition and with taste perception and reported food intake. Although providing exploratory results, it is proposed that the oral microbiota could also be affecting taste and smell perception as well as overall appetite [134–140].
