13 Nutritional Evolution

Mr. Vijit Deepani and Prof. A.K. Kapoor

epgp books

 

Contents:

  • Human nutrition: Basics
  • Evolution in human nutritional pattern: Dietary transition
  • Evidences and implications of Nutritional evolution
  • Summary

 

Learning Objectives:

  • To develop an understanding about dietary transition in course of human evolution.
  • To gain insight about evidences indicating nutritional evolution
  • To understand the implications of nutritional evolution.

 

Human nutrition: Basics

 

The study of diet and nutrition is one of the central and crucial themes in the discipline of human biology as it exhibits a critical interface between cultural, biological and environmental component. Nutritionally, food serves dual purposes for human beings – it provides energy for body processes and physical activity and helps to build the protein and mineral components of the body. These dual motives vary at individual level and also with age, activity and environment.

All human beings must include five major types of nutrients – carbohydrates, lipids (mainly fats and oils), proteins, minerals (including trace elements) and vitamins – in their diet to maintain health and promote growth. These nutrients can be ramified into six principle categories, namely, carbohydrates, fats, protein, vitamins, minerals, and water. The first three nutrients – Carbohydrates, protein and fats – are termed as macronutrients or proximate principles of food as they are needed in relatively large amounts to provide energy to the body. Vitamins and minerals are termed as micronutrients or protective principles of food as they are needed in much smaller amounts and govern several aspects of metabolism. Thus each nutrient performs a distinctive role but their body-building and body-maintaining functions intermingle in several aspects.

 

Bogin (1998) listed and arranged nine universal features of human food and nutrition systems in three broad domains – Biological, Technological and Social (Table I).

 

Table I: Universal attributes of Human food and nutrition system clustered in biological, technological and social domains

 

 

Humans, along the course of evolution, developed the ability to subsist on remarkable diversity of diets so as to sustain life and this dietary plasticity evolved, in part, because of cultural and technological innovations for processing resources, and it allowed human populations to expand into newer and more marginal ecosystems (Leonard, 2012). Further, Leonard and Ulijaszek (2002) emphasized that the nutritional dynamic between human and their environments – the relationship between the intake and expenditure of energy – has crucial adaptive consequences for both survival and reproduction.

 

The pattern of human evolution is significantly influenced by the ecological variation in food availability. In general, humans follow omnivorous diet and have particular nutritional requirements that exhibit dietary adaptation characterized with large amounts of fruit and vegetable material. Omnivorous diet helps humans to select from the many available food resources in order to formulate a cuisine. With regard to nutritional pattern, humans differ from apes in following aspects: (Isaac and Sept, 1988)

  • Former consume higher proportion of animal food than latter
  • Unlike apes, humans lay major emphasis on starchy plant food
  • Humans prefer cooking and preparation tactics to reduce fibrous bulk of these foods and make them palatable.

 

Shukla and Rastogi (2011) opined that nutritional adaptation depends upon the availability of resources and also the mode and degree of their utilization. Various selective pressures, in the course of human evolution, came into play, which led to development of crucial nutritional and physiological differences between human and other primates. Our primate ancestry has led to incorporation of omnivory and several essential nutrients needed in the diet.

 

The following sections throw light upon the evolution of human nutritional pattern and implications of this nutritional evolution.

 

Evolution in human nutritional pattern: Dietary transition

 

The evolutionary history of hominins has been characterized by significant dietary changes, which include the introduction of meat eating, cooking, and the changes associated with plant and animal domestication. Fig I provides glimpse of major stages in relation to dietary transition that probably defined human past.

 

Fig I: Tracing dietary pattern from past to present

(Source: Isaac and Sept, 1988)

Fig II: Timeline indicating major dietary shifts during evolution of hominin forms.

(Source: Luca et al., 2010)

 

The coloured boxes reveal following:

 

Gray boxes: approximate dates of existence for human and chimpanzee/ bonobo-lineage genera. Orange boxes: important dietary transitions in hominin evolution which are supported by strong evidence.

 

Blue boxes: important dietary transitions in hominin evolution which are supported by suggestive inference.

 

Hladik (1981) emphasized that ancestral mammals were insectivores and the invertebrate predation was the basis from which primate dietary pattern evolved. The dietary intake of our early tree dwelling ancestors exhibited resemblance to that of extant arboreal species. Frugivory appeared to be prominent dietary pattern among hominids in Miocene era (Kay, 1977). Their diet comprised of leaf, stalks, fruit twigs and some plant roots. Although the ancestors of modern man possessed the ability to digest animal protein but they subsisted mainly on vegetarian diet.

 

Consumption of animal protein

 

After the descent from the trees and arboreal lifestyle, the ancestors of modern man adopted terrestrial lifestyle, in which the hunting – gathering – scavenging niche helped them to exploit a wide array of nutrients (including both the vegetable and animal protein). The early hominin evolution favoured selection for large molars, thick enamel, and craniofacial robusticity because there is evidence of exploitation of tough foods which lead to rapid tooth wear.

 

On the basis of recent chemical and microwear analysis and examination it was opined that the australopithecines may have exploited cereals, grasses, and sedges more than was previously speculated. The emergence of early Homo is associated with a reduction in mandibular size, robusticity, enamel thickness, and buttressing of mastication. These changes suggest a shift in food use patterns and/or food processing. It has been suggested that our ancestral dietary pattern incorporated higher amount of animal protein after the divergence of human and ape evolutionary lines.

 

It has been established that Homo habilis started to develop stone tools about 2 million years ago and the succeeding species i.e. Homo erectus started to consume large amount of animal protein in 1.8 – 1.6 million years ago (Eaton and Konner, 1985). Afterwards, early humans consumed large amount of animal protein as evidenced by large accumulation of animal remains at their living sites, tools were efficient enough for game hunting and their living sites were located in areas characterized by substantial biomass of land grazing animals (Eaton and Konner, 1985).

 

Fire and cooking

 

As far as dietary transition is concerned, the control and, later, the making of fire was a crucial innovation and Homo erectus is credited with discovery of fire. Bogin (1998) suggested that fire, which may have been used as early as 1.4 million years ago, and was certainly controlled by 750 000 years ago, gave warmth, light, protection and a new technique to process foods.

 

Controlled use of fire led to cooking. The control of fire had a direct and significant effect on human dietary pattern by expanding the range of foods available. Cooking, with application of fire, either by roasting or boiling, enhances the nutritional benefit of several vegetable foods by disintegrating the cellulose component (which is indigestible by people). Fire can help to open large seeds and drive game towards a convenient killing site. Cooking, especially drying or smoking, helps to preserve foods for future storage purpose. Fire helps to burn vegetation to promote new growth to attract grazing and browsing herbivores and to improve the production of certain nuts and other seeds, improved the efficiency of hunting and gathering. All of these uses of fire did not appear at the same time. Many uses of fire seem to be the invention of H. sapiens rather than ancestral species H erectus

 

Goren-Inbar (2004) suggested that the oldest incontrovertible evidence for human-controlled fire dates to 800,000 years ago in Israel. It was emphasized that cooking food may have been part of hominin culture as early as ~1.9 Mya, based on the tooth size reduction observed in Homo erectus that suggests a shift to the processing of softer foods (Wrangham et al, 1999).

 

The increase in brain size was coincident with a decrease in gut size, and this exhibits an improvement in dietary quality (Aiello and Wheeler, Wrangham et al, 1999) but whether such a diet quality change was achieved with the help of cooking or simply by advancements in stone tool technology is a debatable issue.

 

Neolithic revolution: The advent of agriculture and animal domestication

 

The Neolithic era witnessed the phenomenon of domestication of plants and animals. Luca et al (2010) suggested that the origin and spread of agriculture and animal husbandry over the past ~12,000 years, with centers of domestication in Asia, Europe, South America, and Africa, indicate the most recent crucial transition in human dietary pattern. The nutritional shift to agriculture can be expressed as threshold on a gradient of increasing interaction of humans with floral and faunal forms. This involved a steady increment in input of human energy into food production.

 

The advent of agricultural, in Neolithic period, led to reduction in the diversity of foods and the ancestral agricultural population relied upon a less-varied range of floral and faunal forms in comparison to their hunter-gatherer predecessors. The transition from hunter-gatherer phase to agricultural phase resulted in a greater dependence of ancestral human populations upon plant sources or primary producers (particularly seed, root and tuber bearing plants).

 

The process of domestication favored the selection of plants with larger caloric yields and as a result the starch rich food in the form of grains and legumes became the staple diet of ancestral human population at the time of agricultural revolution. Consequently, there was greater carbohydrate intake in diet of early agricultural populations compared with their hunter gatherers predecessors. This further led to nutritional imbalance and to protein and vitamin-deficiency diseases. The effects of nutritional imbalance and deficiencies are still manifest in their skeletal remains. The proportion of carbohydrates eventually increased in their diet, not only because of increasing amount of starch rich food being eaten but also because the domestication process itself selected for plants with larger caloric yields.

 

Thus the human nutritional pattern was significantly altered by shift from hunter-gatherer stage to agricultural stage. This shift led to manifestation of prominent morphological consequences. The Palaeo-indians were big game hunters 10000 years ago, but their descendants started to practice intensive food production, consumed little animal protein and as a result they were considerably shorter in stature (Nickens, 1976) and the skeletal remains exhibit crucial evidence of poor nutritional state. This gave indication of direct effects of protein-calorie deficiency and synergistic interaction between malnutrition and infection (Scrimshaw et al, 1959). But with arrival of industrial revolution, the western diet had started to incorporate adequate animal protein as exhibited by increased average height.

 

Evidences and implications linked with dietary transition

Fig III: Inferring prehistoric diet on basis of the available evidence: the fossil and archaeological record.(Source: Isaac and Sept, 1988)

 

Hominid skeletal evidence (in particular teeth) and archeological sites (yielding animal bones and stone tools) provide crucial evidence in relation to dietary pattern of ancestral population in course of human evolution. Fig III exhibits the time-line of the available fossil and archaeological evidence used to figure out prehistoric diet. The examination of dietary pattern of other primates and the analogy with the behaviour of modern hunter-gatherers also provides important information about the diet of early hominids.

 

Examination of fossil jaw and teeth of extinct hominin forms can offer crucial insight into nutritional evolution. Analysis and examination of various facets of dental evidence such as – the tooth shape, tooth size, enamel shape and dental micro wear along with dental biomechanics – indicate that there has been a transition in the dietary pattern of the australopithecines which has helped them survive in climatic variability (Emes et al., 2011). It was opined by several authorities that the australopithecines possessed smaller incisors in comparison to the molars. It was also speculated that this ratio could be due to terrestrial seed eating habit. The australopithecines were characterized by distinct ‘megadont’ dentition with large, thickly enameled cheek teeth and massive chewing musculature in relation to body size (Walker, 1981). The above statement emphasized that they relied upon heavily masticated diets which comprised of food that needed either strong crushing or long periods of sustained chewing. In contrast, early species of genus Homo, possessed larger incisors and much smaller cheek teeth in comparison to robust australopithecines and the later species Homo erectus and Homo sapiens continue the trend of allometrically reduced post-canine dentition (Walker, 1981) and this indicated that genus Homo had turned to a diet of foods requiring less oral preparations than the foods of australopithecines. It was indicated that genus Homo consumed food that was less fibrous or food that were prepared before ingestion by use of fire or other technology (Isaac and Sept, 1988).

 

The ancient tools (discovered by archaeologists) also provide crucial evidence related to dietary transition (linked with the changing subsistence technology). The earliest evidence of tool use is linked with Homo habilis and the latter used simple, but effective, sharp-edged stone flakes as cutting tools for meat and plant foods (Isaac and Sept, 1988). The diagnostic micro-wear “polish” preserved on the tool edges provided evidence for the use of above mentioned tool type (Keeley and Toth, 1981). The recent technological inventions (i.e. after the emergence of modern Homo sapiens) linked with acquisition and processing of food include bows and arrows, and spear throwers (atlatl); stone sickles used to harvest cereals; grindstones frequently used to grind seeds and storage and cooking devices such as pottery or ovens (Isaac and Sept, 1988).

 

As stated earlier, animal and plant fossil remains found in association with tools at archaeological sites also throw light upon prehistoric human diets. For instance, several bones of large ungulates discovered at the early archaeological sites in east Africa possessed cut marks which were inflicted on them by stone tools which were used to slice off meat (Bunn, 1981; Potts and Shipman, 1981).

 

Coprolite (fossilized faeces) analysis also provides crucial insight into human dietary transition as former reveals something about what people ate, how the food was prepared, the use of condiments to add flavour to food and the use of plants as medicine (Trigg et al, 1994). The odour and visual inspection of the reconstituted coprolite reveal crucial evidence of human food preparation. The H. erectus site of Terra Amata, located on the French Mediterranean, yielded the oldest verified coprolites of a hominid species (Bogin, 1998).

 

The chemical analyses of stable isotopes and trace elements in skeletal remains can provide important clues about broad signature of foods consumed at the time. One widely devised method is the determination of the ratio of delta 15nitrogen ( 15N) to delta 13carbon ( 13C). The amount of 13C reveals magnitude of plant-based foods in the diet whereas the amount of 15N indicates the magnitude of animal protein in the diet. The ratio of the trace element strontium to calcium (Sr/Ca) can also be employed in similar context (diet reconstruction) where a higher ratio represents that more plant food than animal food was consumed by the animal.

 

It was observed that, with time, Sr/Ca ratios in bone increased which indicated the dominance of plant food in the diet (Bogin, 1998). But the increase presented itself 20000 years after the modern human form appeared in the fossil record and it seems that the morphological shift from archaic to modern human form was not due to the utilization of new foods but due to advancement in the technology for both acquiring and processing existing foods and these improvements decreased human physical labour and resulted in a less muscular body and a more gracile skeleton (Bogin, 1998).

 

Implications

 

The table given below (Table II) throws light upon evolutionary modifications in hominin brain size (cubic centimetres), estimated adult male and female body mass (kilograms) and posterior tooth area (square millimetres) (data from McHenry, 1992,1994; Gabunia et al., 2000, 2001; McHenry and Coffing, 2000; AntÓn and Swisher, 2001). These modifications represent implications to dietary transition among hominin forms.

TABLE II: Variation in Brain Size (cm3), Post-canine Tooth Surface Areas (mm2) and Estimated Male and Female Body Weights (kg) for certain prominent fossil hominin Species in relation to Geological time period (Million years ago)

 

(Source: Leonard el al., 2007)

 

As emphasized by the table, over a time period between 4.0 and 1.5 million years ago (approx.), the australopithecines exhibited only moderate evolution of brain size but with the evolution of the genus Homo, there was substantial increment in brain size, with the average cranial capacities of Homo habilis being over 600 cm3, and representatives of Homo erectus being 850-1000 cm3. The modifications in the cranial and dental anatomy of Homo erectus indicate that these forms exhibited different dietary pattern than their australopithecine ancestors. There was dramatic increase in the total surface area of grinding teeth (molars and premolars) in course of evolution of the australopithecines from 460 mm2 (in Australopithecus afarensis) to 756 mm2 (in Australopithecus boisei). This indicates that australopithecines consumed a heavily masticated diet.

 

It was suggested that with the appearance of Homo erectus in East Africa (at 1.8 million years ago), there was: (Wolpoff, 1999; Wood and Collard, 1999; AntÓn et al., 2002)

 

(1) Significant increment in brain and body size

(2) Reductions of posterior tooth size and craniofacial robusticity

(3) The evolution of human-like limb proportions and

(4) Significant changes in foraging/ subsistence

 

Summary

 

The diet and nutrition of an individual is shaped by cultural, biological and environmental component. Nutritional evolution (in relation to humans) simply relates to dietary transition or variation at various evolutionary stages of man. At each stage of development, nutritional evolution represents interaction between man and his culture and environment accompanied with prominent morphological and anatomical consequences. Humans live in diverse environmental settings and utilize certain subsistence tactics which are linked with selective pressures on human metabolism and homeostasis. Prominent dietary changes in course of human evolution include the introduction of meat eating, discovery of fire and advent of cooking technique, and the changes associated with plant and animal domestication. The diet of early tree dwelling ancestors was comprised of leaf, stalks, fruit twigs and some plant roots (as commonly observed among extant monkey and apes). But after transition to terrestrial lifestyle (from arboreal lifestyle) they started to inculcate animal protein along with vegetable protein in their diet. Human ancestral forms, then for a very long time period, were characterized by varied diet which combined proportions of fibre and starch rich food, meats, nuts and fruits. This diverse diet was supported by the innovation of cooking strategy and controlled use of fire. But with advent of agriculture and animal domestication, and improvement in technology, humans began to incorporate less diverse (or less balanced) diet.

 

Examination of hominid skeletal evidence (especially teeth and jaw remains) and archeological sites (yielding animal bones and stone tools) provide crucial evidence which help to infer dietary pattern of ancestral population in course of human evolution. Thus the comprehensive understanding of nutritional evolution can be achieved with study of fossil evidences and archaeological records along with assessment of morphological consequences.

 

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