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'''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 |pmid=23090991 |bibcode=2012PNAS..10918571F |pmc=3494886 }}</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 |url-access=subscription }}</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.
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Context biases result from individuals using clues about the social structure of their population to determine what cultural variants to adopt. This determination is made without reference to the content of the variant. There are two major categories of context biases: model-based biases, and frequency-dependent biases.
Model-based biases result when an individual is biased to choose a particular "cultural model" to imitate. There are four major categories of model-based biases: prestige bias, skill bias, success bias, and similarity bias.<ref name="McElreath" /><ref>{{cite journal |last1=Henrich |first1=Joseph |last2=McElreath |first2=Richard |title=The evolution of cultural evolution |journal=Evolutionary Anthropology: Issues, News, and Reviews |date=January 2003 |volume=12 |issue=3 |pages=123–135 |doi=10.1002/evan.10110 }}</ref> A "prestige bias" results when individuals are more likely to imitate cultural models that are seen as having more [[:wikt:prestige|prestige]]. A measure of prestige could be the amount of deference shown to a potential cultural model by other individuals. A "skill bias" results when individuals can directly observe different cultural models performing a learned skill and are more likely to imitate cultural models that perform better at the specific skill. A "success bias" results from individuals preferentially imitating cultural models that they determine are most generally successful (as opposed to successful at a specific skill as in the skill bias.) A "similarity bias" results when individuals are more likely to imitate cultural models that are perceived as being similar to the individual based on specific traits.
Frequency-dependent biases result when an individual is biased to choose particular cultural variants based on their perceived frequency in the population. The most explored frequency-dependent bias is the "conformity bias." Conformity biases result when individuals attempt to copy the mean or the mode cultural variant in the population. Another possible frequency dependent bias is the "rarity bias." The rarity bias results when individuals preferentially choose cultural variants that are less common in the population. The rarity bias is also sometimes called a "nonconformist" or "anti-conformist" bias.
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*{{cite book|last=Sterelny|first=Kim|others=Stephen Shennan|title=Review Genes, Memes and Human History|publisher=Thames and Hudson|___location=London|year=2002|pages=304|url=http://www.vuw.ac.nz/phil/staff/documents/sterelny-papers/tripod.pdf#search='dual%20inheritance%20theorypdf'}}
*{{cite journal | last1 = Laland | first1 = K.N. | last2 = Odling-Smee | first2 = J. | last3 = Myles | first3 = S. | year = 2010 | title = How culture shaped the human genome: bringing genetics and the human sciences together | journal = Nature Reviews Genetics | volume = 11 | issue = 2| pages = 137–148 | doi=10.1038/nrg2734 | pmid=20084086| s2cid = 10287878 }}
* {{cite journal |last1=Ovcharov |first1=Dmitry |title=The ideas of genetic and cultural evolution in the Philosophy of the 20th Century: a Historical and philosophical analytical review |journal=Bulletin of the Moscow State Pedagogical University. The "Philosophical Sciences"
===Journal articles===
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{{DEFAULTSORT:Dual Inheritance Theory}}
[[Category:1960s introductions]]
[[Category:Theories]]
[[Category:Anthropology]]
[[Category:Behavioural genetics]]
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