role did diet play in the evolution of hominids?
Importance of diet in the evolution of hominids
Introduction and overview prevalent theoretical stance used to explain the early processes of human evolution is that environment and bipedality are seen as primary factors in this process. “Modern theories of evolution consider the environment to be the directive force in the evolutionary process…” (Dobzhansky 122). However, this view is countered by those scholars who see diet as one of the primary and essential aspects in selection and early evolution. A study by Teaford and Ungar (2000), Diet and the evolution of the earliest human ancestors, states that,
Since the discovery of Australopithecus afarensis, many researchers have emphasized the importance of bipedality in scenarios of human origins… Surprisingly, less attention has been focused on the role played by diet in the ecology and evolution of the early hominids (Teaford and Ungar, 2000)
This study and others indicate that there is an increasing interest in the significance of the diets of early hominids in many fields, including paleoenvironmental studies and primatology. An important aspect that has fueled this interest is the fact that new fossil findings from the early Pliocene have raised intriguing questions about the importance of change in diet in the early evolution of the Hominidae. As Teaford and Ungar (2000) state, ” in short, we need to focus not just on how the earliest hominids moved between food patches, but also on what they ate when they got there” (Teaford and Ungar, 2000).
This emphasis on the role of diet in evolution is also related to dentistry studies of fossils. There is a strong indication of a radical change in diet in this area of research. It has been found that early hominids all had, “…small- to moderate-sized incisors; large, flat molars with little shear potential; a ratio of first to third molar area that was low compared with those of extant apes…”(Teaford and Ungar, 2000). As well as this, hominids had thick tooth enamel; and thick mandibular corpora, which suggest, “… A dietary shift at or near the stem of hominid evolution” (Teaford and Ungar, 2000).
A central finding is that the early hominids had the capability of grinding down both hard and soft foods. This has certain important evolutionary outcomes. As Teaford and Ungar, (2000), state,
The early hominids could also have eaten both abrasive and nonabrasive foods. This ability to eat both hard and soft foods, plus abrasive and nonabrasive foods, would have left the early hominids particularly well suited for life in a variety of habitats, ranging from gallery forest to open savanna. (Teaford and Ungar, 2000).
This viewpoint therefore suggests that the variety of diet and the ability to deal with both hard and soft foods allowed for a greater scope in evolutionary selection and a wider choice of selection possibilities. This in turn suggests rather obvious possibilities in terms social structure and the ability to choose various and different habitats instead of being restricted to one single type of habitat.
There are a number of compelling studies that assert that the diet of early hominids could have played a vital role in evolution and the process of selection. There is a certain consensus among many scholars that the hominids began to experiment with harder foods and to change their diet from softer foods. This change had the important result of allowing our earlier ancestors “… The flexibility to cope with short-term and long-term climatic variations and the resultant changes in resource availability” (Teaford and Ungar, 2000).
This view is also echoed in other journal articles. In the article Food for thought: Dietary Change was a Driving Force in Human Evolution by Leonard (2002), the author states that, growing body of evidence indicates that these miscellaneous quirks of humanity in fact have a common thread: they are largely the result of natural selection acting to maximize dietary quality and foraging efficiency. Changes in food availability over time, it seems, strongly in-uenced our hominid ancestors. Thus, in an evolutionary sense, we are very much what we ate. (Leonard 108)
This view is supported by studies of cranial and dental traits of the hominids, which indicate a dramatic change in dietary capabilities between 4 million and 2.3 million years ago. This reiterates the view that diet enabled the hominids to live in a variety of habitats and to adapt to resource availability and to any climate fluctuations that would produce different food possibilities. (Eaton et al., 2002)
This change in diet in hominid development is also stressed in a study by Sponheimer and Lee-Thorp (1999). This study suggests that the change in diet in fact led to an increase in protein rich foods and had an important effect on the evolutionary process. The study suggests that early hominids not only eat fruits and leaves but also carbon-13-enriched foods such as grasses and sedges or animals. This study also asserts that the adaptation to high qaulity foods is seen as possible precursors to development of stone tools and the origin of the genus Homo.
There are many other theoretical views about the effect of diet on the early evolutionary process. For examples, the view that bipedalism was influenced by the adaptation of a posture to obtain foods that had previously been out of reach. (Leonard 109) However, one of the most important aspects of the role of diet in the evolutionary and selection process is the possible way in which diet affected development of the brain.
2. Brain power and diet
There is substantial evidence of the link between increased brain capacity and power and evolution and diet.
Leonard notes that we use a.
A greater share of our daily energy budget to feed our voracious brains. In fact, at rest brain metabolism accounts for a whopping 20 to 25% of an adult human’s energy needs — far more than the 8 to 10% observed in nonhuman primates, and more still than the 3 to 5% allotted to the brain by other mammals.
Leonard also suggests that brain expansion could not have taken place without a diet which was sufficiently rich in calories and nutrients to meet the associated energy costs. (Leonard 111) This of course implies a radial change in diet in the lives of the early hominids – as has already been suggested in other studies discussed above.
This view is also supported by various comparative studies of living animals. “Across all primates, species with bigger brains dine on richer foods, and humans are the extreme example of this correlation, boasting the largest relative brain size and the choicest diet” (Leonard 111).
An important theoretical view in this regard is the Expensive-Tissue Hypotheses. This theory suggests that there is a direct correlation between the size of the brain and the gut. It asserts that the larger the brain the smaller the gut. This theory is based on the finding that, ” Gut size is highly correlated with diet, and relatively small guts are compatible only with high-quality, easy-to-digest food ” (Aiello and Wheeler 199) This leads to the important conclusion that,
No matter what is selecting for relatively large brains in humans and other primates, they cannot be achieved without a shift to a high-quality diet unless there is a rise in the metabolic rate. Therefore the incorporation of increasingly greater amounts of animal products into the diet was essential in the evolution of the large human brain.
Aiello and Wheeler 199)
In other words, the correlation between brain size and gut size suggests a correlation with rich diets that include animal fats. These findings coincide with other findings from dentistry research. Therefore, it seems that diet played a major role in selecting for a large brain and its more powerful functioning.
Another study that adds to the research on the topic of diet and brain size suggests that larger brains have certain metabolic requirements and consequences. This refers to the view the larger the brain the greater will be the overall physical energy budget. Based on this assumption, the large brain has to be supported by a diet that is rich in nutrients. (Leonard et al., 2002)
Another more comprehsive study by Blumenberg et al. (1983) entitled the Evolution of the Advanced Hominid Brain, provides a clear and interesting analysis of the possible linkage between the ingestion of certain types of foods and their concomitant chemical and neurological consequences. This study notes that the eating of meat or the preferential feeding on the livers of carnivores would lead to the ingestion of important nutrients such as calcium. This change in diet could have had a dramatic effect on the size and composition of the brain.
An increase in certain foraging behaviors associated with carnivory would entail elevated exercise levels for those participating. C a L -concentration influences several processes at the synaptic terminal…Such effects on synaptic strength and plasticity may have accelerated the development of various components of learning and memory processes.
Blumenberg et al. 598)
The study concludes that, “These few observations provide a fascinating window into the way in which new dietary regimes can affect neurotransmitter synthesis and thereby influence broad-based activity patterns in the brain” (Blumenberg et al. 598).
There are many theories about the way that diet affected evolutionary selection in hominids. There is little doubt that diet played a significant role and that brain size is related to a radical change of diet in the distant past. However, what scholars are also at pains to point out is that diet should be seen in conjunction with and in relation to other factors, such as social structure. As Spuhler (1959) states,
The change to a partially carnivorous diet had extremely broad implications for the social organization of early hominoids” (Diet, Evolution, and Culture). Diet and other factors should be considered in the intricate and immensely complex task of attempting to understand our origins through the evolutionary selection process of hominids.
Dobzhansky, Theodosius. Evolution, Genetics, and Man. New York: John Wiley & Sons, 1955.
Aiello L. And Wheeler P. The Expensive-Tissue Hypothesis: the Brain and the Digestive System in Human and Primate Evolution. Current Anthropology, Vol. 36, No. 2. (Apr., 1995), pp. 199-221. December 2, 2007. http://links.jstor.org/sici?sici=0011-3204%28199504%2936%3A2%3C199%3ATEHTBA%3E2.0.CO%3B2-9
Blumenberg B. et al., the Evolution of the Advanced Hominid Brain
Current Anthropology, Vol. 24, No. 5. (Dec., 1983), pp. 589-623. December 1, 2007. http://links.jstor.org/sici?sici=0011-3204%28198312%2924%3A5%3C589%3ATEOTAH%3E2.0.CO%3B2-W
Diet, Evolution, and Culture. December 1, 2007. http://www.beyondveg.com/billings-t/comp-anat/comp-anat-3c.shtml
Eaton, S. Boyd, Stanley B. Eaton, and Loren Cordain. “Chapter 2 Evolution, Diet, and Health.” Human Diet: Its Origin and Evolution. Ed. Peter S. Ungar and Mark F. Teaford. Westport, CT: Bergin and Garvey, 2002. 7-17.
Howells, William. Mankind in the Making: The Story of Human Evolution. Revised ed. Garden City, NY: Doubleday, 1967..
Leonard W. Food for thought: Dietary Change was a Driving Force in Human
Evolution. SCIENTIFIC AMERICAN. 2002.
Leonard W. Robertson M. Snodgrass J. And Kuzawa C. Metabolic correlates of hominid brain evolution. Laboratory for Human Biology Research, Department of Anthropology, Northwestern University. http://web.ebscohost.com.libproxy2.usouthal.edu/ehost/detail?vid=5&hid=117&sid=99f5dc9d-c950-4b64-aef1-807528e43f21%40sessionmgr8
Sponheimer M. And Lee-Thorp J. Isotopic Evidence for the Diet of an Early Hominid, Australopithecus africanus. Science 15 January 1999: Vol. 283. no. 5400, pp. 368-370. November 30, 2007. http://www.sciencemag.org.libproxy2.usouthal.edu/cgi/content/full/283/5400/368?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=Diet+hominids&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT
Teaford M. And Ungar P. Diet and the evolution of the earliest human ancestors PNAS, December 5, 2000, vol. 97, no. 25. November 30, 2007. http://www.pnas.org.libproxy2.usouthal.edu/cgi/content/full/97/25/13506 www.questia.com/PM.qst?a=o&d=101313742
Ungar, Peter S., and Mark F. Teaford, eds. Human Diet: Its Origin and Evolution. Westport, CT: Bergin and Garvey, 2002.
Diet in the evolution of hominids
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