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'''Lactase persistence'''
One of the best known examples is the prevalence of the genotype for adult lactose absorption in human populations, such as Northern Europeans and some African societies, with a long history of raising cattle for milk. Until around 7,500 years ago,<ref name="Itan Powell Beaumont et al Origins of Lactase Persistence">{{cite journal |last1=Itan |first1=Yuval |last2=Powell |first2=Adam |last3=Beaumont |first3=Mark A. |last4=Burger |first4=Joachim |last5=Thomas |first5=Mark G. |title=The Origins of Lactase Persistence in Europe |journal=
'''Food processing'''
Culture has driven changes to the human digestive systems making many digestive organs, such as teeth or stomach, smaller than expected for primates of a similar size,<ref name=":2">{{Cite journal|last1=Aiello|first1=Leslie C.|last2=Wheeler|first2=Peter|date=1995-01-01|title=The Expensive-Tissue Hypothesis: The Brain and the Digestive System in Human and Primate Evolution|jstor=2744104|journal=Current Anthropology|volume=36|issue=2|pages=199–221|doi=10.1086/204350|s2cid=144317407}}</ref> and has been attributed to one of the reasons why humans have such large brains compared to other great apes.<ref name="Fonseca-Azevedo 18571–18576">{{cite journal |last1=Fonseca-Azevedo |first1=Karina |last2=Herculano-Houzel |first2=Suzana |title=Metabolic constraint imposes tradeoff between body size and number of brain neurons in human evolution |journal=Proceedings of the National Academy of Sciences |date=6 November 2012 |volume=109 |issue=45 |pages=18571–18576 |doi=10.1073/pnas.1206390109 |doi-access=free |bibcode=2012PNAS..10918571F }}</ref><ref>{{Cite journal|last=Gorman|first=Rachael Moeller|title=Cooking Up Bigger Brains|journal=Scientific American|language=en|volume=298|issue=1|pages=102–105|doi=10.1038/scientificamerican0108-102|pmid=18225702|year=2008|bibcode=2008SciAm.298a.102G}}</ref> This is due to food processing. Early examples of food processing include pounding, marinating and most notably cooking. Pounding meat breaks down the muscle fibres, hence taking away some of the job from the mouth, teeth and jaw.<ref>{{cite journal |last1=Farrell |first1=J. H. |title=The effect on digestibility of methods commonly used to increase the tenderness of lean meat |journal=British Journal of Nutrition |date=May 1956 |volume=10 |issue=2 |pages=111–115 |doi=10.1079/bjn19560019 |pmid=13315930 |doi-access=free }}</ref><ref>{{cite book |last1=Henrich |first1=Joseph |title=The Secret of Our Success: How Culture Is Driving Human Evolution, Domesticating Our Species, and Making Us Smarter |date=2015 |publisher=Princeton University Press |isbn=978-1-4008-7329-6 |page=66 }}</ref> Marinating emulates the action of the stomach with high acid levels. Cooking partially breaks down food making it more easily digestible. Food enters the body effectively partly digested, and as such food processing reduces the work that the digestive system has to do. This means that there is selection for smaller digestive organs as the tissue is energetically expensive,<ref name=":2" /> those with smaller digestive organs can process their food but at a lower energetic cost than those with larger organs.{{sfn|Wrangham|2009|p=40}} Cooking is notable because the energy available from food increases when cooked and this also means less time is spent looking for food.<ref name="Fonseca-Azevedo 18571–18576" /><ref name="Carmody Wrangham energetic significance">{{cite journal |last1=Carmody |first1=Rachel N. |last2=Wrangham |first2=Richard W. |title=The energetic significance of cooking |journal=Journal of Human Evolution |date=October 2009 |volume=57 |issue=4 |pages=379–391 |doi=10.1016/j.jhevol.2009.02.011 |pmid=19732938 |bibcode=2009JHumE..57..379C |s2cid=15255649 |url=http://nrs.harvard.edu/urn-3:HUL.InstRepos:5283945 }}</ref><ref>{{cite journal |last1=Carmody |first1=Rachel N. |last2=Weintraub |first2=Gil S. |last3=Wrangham |first3=Richard W. |title=Energetic consequences of thermal and nonthermal food processing |journal=Proceedings of the National Academy of Sciences |date=29 November 2011 |volume=108 |issue=48 |pages=19199–19203 |doi=10.1073/pnas.1112128108 |pmc=3228431 |pmid=22065771 |bibcode=2011PNAS..10819199C |doi-access=free }}</ref>
Humans living on cooked diets spend only a fraction of their day chewing compared to other extant primates living on raw diets. American girls and boys spent on average 7 to 8 percent of their day chewing respectively (1.68 to 1.92 hours per day), compared to chimpanzees, who spend more than 6 hours a day chewing.{{sfn|Wrangham|2009|p=140}} This frees up time which can be used for hunting. A raw diet means hunting is constrained since time spent hunting is time not spent eating and chewing plant material, but cooking reduces the time required to get the day's energy requirements, allowing for more subsistence activities.{{sfn|Wrangham|2009|p=142}} Digestibility of cooked carbohydrates is approximately on average 30% higher than digestibility of non-cooked carbohydrates.<ref name="Carmody Wrangham energetic significance"/><ref>{{Citation|last=University of California Television (UCTV)|title=CARTA: The Evolution of Human Nutrition -- Richard Wrangham: Fire Starch Meat and Honey|date=2013-03-21|url=https://www.youtube.com/watch?v=VnN-QeMgJ_U |archive-url=https://ghostarchive.org/varchive/youtube/20211219/VnN-QeMgJ_U |archive-date=2021-12-19 |url-status=live|access-date=2017-03-27}}{{cbignore}}</ref> This increased energy intake, more free time and savings made on tissue used in the digestive system allowed for the selection of genes for larger brain size.
Despite its benefits, brain tissue requires a large amount of calories, hence a main constraint in selection for larger brains is calorie intake. A greater calorie intake can support greater quantities of brain tissue. This is argued to explain why human brains can be much larger than other apes, since humans are the only ape to engage in food processing.<ref name="Fonseca-Azevedo 18571–18576"/> The cooking of food has influenced genes to the extent that, research suggests, humans cannot live without cooking.<ref name="Koebnick Strassner Hoffmann Leitzmann Consequences of a Long-Term Raw Food Diet">{{cite journal |last1=Koebnick |first1=C. |last2=Strassner |first2=C. |last3=Hoffmann |first3=I. |last4=Leitzmann |first4=C. |title=Consequences of a Long-Term Raw Food Diet on Body Weight and Menstruation: Results of a Questionnaire Survey |journal=Annals of Nutrition and Metabolism |date=1999 |volume=43 |issue=2 |pages=69–79 |doi=10.1159/000012770 |pmid=10436305 |s2cid=30125503 }}</ref><ref name="Fonseca-Azevedo 18571–18576" /> A study on 513 individuals consuming long-term raw diets found that as the percentage of their diet which was made up of raw food and/or the length they had been on a diet of raw food increased, their BMI decreased.<ref name="Koebnick Strassner Hoffmann Leitzmann Consequences of a Long-Term Raw Food Diet"/> This is despite access to many non-thermal processing, like grinding, pounding or heating to 48 °C. (118 °F).<ref name="Koebnick Strassner Hoffmann Leitzmann Consequences of a Long-Term Raw Food Diet"/> With approximately 86 billion neurons in the human brain and 60–70 kg body mass, an exclusively raw diet close to that of what extant primates have would be not viable as, when modelled, it is argued that it would require an infeasible level of more than nine hours of feeding every day.<ref name="Fonseca-Azevedo 18571–18576" /> However, this is contested, with alternative modelling showing enough calories could be obtained within 5–6 hours per day.<ref name="Cornélio de Bittencourt-Navarrete et al Human Brain Expansion"/> Some scientists and anthropologists point to evidence that brain size in the Homo lineage started to increase well before the advent of cooking due to increased consumption of meat<ref name=":2" /><ref name="Cornélio de Bittencourt-Navarrete et al Human Brain Expansion">{{cite journal |last1=Cornélio |first1=Alianda M. |last2=de Bittencourt-Navarrete |first2=Ruben E. |last3=de Bittencourt Brum |first3=Ricardo |last4=Queiroz |first4=Claudio M. |last5=Costa |first5=Marcos R. |title=Human Brain Expansion during Evolution Is Independent of Fire Control and Cooking |journal=Frontiers in Neuroscience |date=25 April 2016 |volume=10 |page=167 |doi=10.3389/fnins.2016.00167 |pmc=4842772 |pmid=27199631 |doi-access=free }}</ref><ref>{{Cite web|url=http://www.berkeley.edu/news/media/releases/99legacy/6-14-1999a.html|title=06.14.99 - Meat-eating was essential for human evolution, says UC Berkeley anthropologist specializing in diet|website=www.berkeley.edu|access-date=2017-03-27}}</ref> and that basic food processing (slicing) accounts for the size reduction in organs related to chewing.<ref>{{cite journal |last1=Zink |first1=Katherine D. |last2=Lieberman |first2=Daniel E. |title=Impact of meat and Lower Palaeolithic food processing techniques on chewing in humans |journal=Nature |date=24 March 2016 |volume=531 |issue=7595 |pages=500–503 |doi=10.1038/nature16990 |pmid=26958832 |bibcode=2016Natur.531..500Z |s2cid=4384345 }}</ref> Cornélio et al. argues that improving cooperative abilities and a varying of diet to more meat and seeds improved foraging and hunting efficiency. It is this that allowed for the brain expansion, independent of cooking which they argue came much later, a consequence from the complex cognition that developed.<ref name="Cornélio de Bittencourt-Navarrete et al Human Brain Expansion"/> Yet this is still an example of a cultural shift in diet and the resulting genetic evolution. Further criticism comes from the controversy of the archaeological evidence available. Some claim there is a lack of evidence of fire control when brain sizes first started expanding.<ref name="Cornélio de Bittencourt-Navarrete et al Human Brain Expansion"/><ref>{{cite journal |last1=Roebroeks |first1=Wil |last2=Villa |first2=Paola |title=On the earliest evidence for habitual use of fire in Europe |journal=Proceedings of the National Academy of Sciences |date=29 March 2011 |volume=108 |issue=13 |pages=5209–5214 |doi=10.1073/pnas.1018116108 |pmc=3069174 |pmid=21402905 |bibcode=2011PNAS..108.5209R |doi-access=free }}</ref> Wrangham argues that anatomical evidence around the time of the origin of ''[[Homo erectus]]'' (1.8 million years ago), indicates that the control of fire and hence cooking occurred.<ref name="Carmody Wrangham energetic significance"/> At this time, the largest reductions in tooth size in the entirety of human evolution occurred, indicating that softer foods became prevalent in the diet. Also at this time was a narrowing of the pelvis indicating a smaller gut and also there is evidence that there was a loss of the ability to climb which Wrangham argues indicates the control of fire, since sleeping on the ground needs fire to ward off predators.{{sfn|Wrangham|2009|pp=98–102}} The proposed increases in brain size from food processing will have led to a greater mental capacity for further cultural innovation in food processing which will have increased digestive efficiency further providing more energy for further gains in brain size.{{sfn|Wrangham|2009|p=127}} This positive feedback loop is argued to have led to the rapid brain size increases seen in the ''Homo'' lineage.{{sfn|Wrangham|2009|p=127}}<ref name="Cornélio de Bittencourt-Navarrete et al Human Brain Expansion"/>
==Mechanisms of cultural evolution==
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