Encephalisation and impact on our diet pattern: Anthropological perspective
Encephalisation and impact on our diet pattern: An anthropological perspective
The evolutionary instinct of over feeding exposes human body to a consistently higher concentration of energy nutrients (like glucose) which leads to energy storage as fats (predisposition to obesity) and relatively higher amounts of insulin (for glucose uptake) and leptin (for fat storage). When in excess (contrary to their normal function) these two hormones prompt the brain for increased appetite (signaling the brain about unavailability of ready energy).
Encephalization is the most important feature that distinguishes us from other primates having great impacts on human nutritional biology because energy requirements of nervous tissue (including brain) are approximately 16 times that of skeletal muscles. This indicates that large brain size is energetically extremely expensive
Primate brain is thrice as big as compared to other mammals of comparable size and human brain is three times bigger than that of other primates of similar size. This means that humans have nine times greater proportions of brain tissue than other non-primate mammals.
As a consequence of high energy needs, humans arguably consume food that is rich in energy. It is important to note that in order to meet the needs of higher energy to the brain; we consume much better quality diets in comparison to all other primates. Additionally, the staple food of all human communities, geographies, and ethnicities around the world is substantially denser in energy than that of all other primates
Most primates have large gut size (particularly colon which allows fermentation of plant fiber) for fibrous low quality diet but humans in comparison have radically smaller gut size. The human gut size reduction is an adaptation for high quality and easily digestible diet meaning that encephalization would have demanded high quality diet and reduced gut size. The size of brain in genus Homo has tripled (or more) in the past 4 million years. It has gone from 400 cm3 in australopithecines to 1300-1400 cm3 in humans. This manifest increase in brain size was highest in human lineage at about 2.0 to 1.7 million years ago (mya), the time when human ancestors learned the use of fire to cook food for increasing diet quality and when presumably considerable reduction in gut size might have taken place. This process was more prominent in Homo erectus in which the brain size increased noticeably on higher pace as against australopithecines.
Bipedal locomotion and encephalization appeared almost simultaneously in evolution suggesting some evolutionary affiliation between the two. It presumably occurred because our ancestors 4 mya had to look for alternative forms of food in drastically changing climates of African savanna. They needed free hands to break nuts and tubers and also handle tools for hunting in the next 2-3 million years.
Climatic shift in African savanna:
Human ancestors lived in African savanna some 4 mya. It is the time when the climate of this region was rapidly changing with environment turning extremely dry. This resulted in a decline in forest area and an increase in open woodlands and grasslands. Such climatic shift in the homeland of our ancestors would have resulted in great impact on food distribution patterns posing special challenges to our hominin ancestors. A key milestone was crossed at that time because animal food became more abundant and consequently was the food of choice. This is because savannas have a very low net primary energy productivity as against woodlands but the herbivore productivity in savannas is three times (10.2 kcal/m2/yr) as compared to woodlands . In addition to improvements in dietary quality by changing climates (a blessing in disguise), African savanna animal food repertoire provided higher proportions of fatty acids that might have been indispensible for hominin brain enlargement.
Thrifty and selfish genetics:
With the climatic shift and food resource redistribution in African savanna 4 mya, food stability must have been jeopardized in hominin lineages. Initiation of an evolutionary process for high energy food intake in greater proportions (thrift) and greater craving for higher energy foods (selfishness) in our ancestors living then would have set into play. With time, the hominin lineages, unto modern humans, developed a consistent sense of craving for high-calorie food fulfilling the objectives of evolutionary wisdom as abundant food was unavailable now. This established a genetic property in H. sapiens now referred to as thrifty gene hypothesis. Food scarcity in the past and redistribution of food pattern in changing climates must have set the instinct for higher food intake and storage and that is where we derive our first postulate “Evolutionary instinct” from. Even in the modern times, we live with these thrifty and selfish genes but our food quality and availability has sharply increased leading to extremely high energy intake and storage and, therefore, much higher propensity to diabetes and obesity.