View source for Biology:Dual inheritance theory

{{Short description|Theory of human behavior}}

'''Dual inheritance theory''' ('''DIT'''), also known as '''gene–culture coevolution''' or '''biocultural evolution''',<ref>{{cite web|last=O'Neil|first=Dennis|title=Glossary of Terms|url=http://anthro.palomar.edu/synthetic/glossary.htm#sectB|work=Modern Theories of Evolution|access-date=28 October 2012}}</ref> was developed in the 1960s through early 1980s to explain how human behavior is a product of two different and interacting [[Biology:Evolution|evolution]]ary processes: genetic evolution and cultural evolution. Genes and culture continually interact in a feedback loop:<ref>{{Cite journal|last=Laland|first=Kevin N.|date=2008-11-12|title=Exploring gene–culture interactions: insights from handedness, sexual selection and niche-construction case studies|journal=Philosophical Transactions of the Royal Society B: Biological Sciences|language=en|volume=363|issue=1509|pages=3577–3589|doi=10.1098/rstb.2008.0132|issn=0962-8436|pmc=2607340|pmid=18799415}}</ref> changes in genes can lead to changes in culture which can then influence genetic selection, and vice versa. One of the theory's central claims is that culture evolves partly through a Darwinian selection process, which dual inheritance theorists often describe by analogy to genetic evolution.<ref>{{cite book|last1=Richerson|first1= Peter J.|last2=Boyd|first2= Robert|title=Not By Genes Alone: How Culture Transformed Human Evolution|publisher=University of Chicago Press|year=2005|url=http://www.press.uchicago.edu/ucp/books/book/chicago/N/bo3615170.html}}</ref>

'Culture', in this context is defined as 'socially learned behavior', and 'social learning' is defined as copying behaviors observed in others or acquiring behaviors through being taught by others. Most of the modelling done in the field relies on the first dynamic (copying) though it can be extended to teaching. Social learning at its simplest involves blind copying of behaviors from a model (someone observed behaving), though it is also understood to have many potential biases, including success bias (copying from those who are perceived to be better off), status bias (copying from those with higher status), homophily (copying from those most like ourselves), conformist bias (disproportionately picking up behaviors that more people are performing), etc.  Understanding social learning is a system of pattern replication, and understanding that there are different rates of survival for different socially learned cultural variants, this sets up, by definition, an evolutionary structure: cultural evolution.<ref>{{cite journal|last1=Campbell|first1=D. T.|title=Variation and selective retention in socio-cultural evolution|journal=Social Change in Developing Areas, A Reinterpretation of Evolutionary Theory|date=1965}}</ref>

Because genetic evolution is relatively well understood, most of DIT examines cultural evolution and the interactions between cultural evolution and genetic evolution.

==Theoretical basis==

DIT holds that genetic and cultural evolution interacted in the evolution of ''Homo sapiens''.  DIT recognizes that the natural selection of genotypes is an important component of the evolution of human behavior and that cultural traits can be constrained by genetic imperatives. However, DIT also recognizes that genetic evolution has endowed the human species with a parallel evolutionary process of cultural evolution. DIT makes three main claims:<ref name="McElreath">{{cite book |author1=McElreath, R. |author2=Henrich, J. |year=2007 |chapter-url=http://arbeit.ucdavis.edu/mcelreath/files/Henrich%20and%20McElreath%20final.pdf |chapter=Dual inheritance theory: the evolution of human cultural capacities and cultural evolution |editor=R. Dunbar and L. Barrett |title=Oxford Handbook of Evolutionary Psychology |location=Oxford |publisher=Oxford University Press |url-status=dead |archive-url=https://web.archive.org/web/20070811175148/http://arbeit.ucdavis.edu/mcelreath/files/Henrich%20and%20McElreath%20final.pdf |archive-date=2007-08-11 }}</ref>

===Culture capacities are adaptations===

The human capacity to store and transmit culture arose from genetically evolved psychological mechanisms.  This implies that at some point during the evolution of the human species a type of [[Philosophy:Observational learning|social learning]] leading to cumulative cultural evolution was evolutionarily advantageous.

===Culture evolves===

Social learning processes give rise to cultural evolution.  Cultural traits are transmitted differently from genetic traits and, therefore, result in different population-level effects on behavioral variation.

===Genes and culture co-evolve===

Cultural traits alter the social and physical environments under which genetic selection operates.  For example, the cultural adoptions of agriculture and dairying have, in humans, caused genetic selection for the traits to digest starch and [[Chemistry:Lactose|lactose]], respectively.<ref>{{cite journal | last1 = Simoons | first1 = F | year = 1969 | title = Primary adult lactose intolerance and the milking habit: A problem in biologic and cultural interrelations: I. Review of the medical research | journal = The American Journal of Digestive Diseases | volume = 14 | issue = 12| pages = 819–836 | doi=10.1007/bf02233204 | pmid=4902756| s2cid = 22597839 }}</ref><ref>{{cite journal | last1 = Simoons | first1 = F | year = 1970 | title = Primary adult lactose intolerance and the milking habit: A problem in biologic and cultural interrelations: II. A culture historical hypothesis | journal = The American Journal of Digestive Diseases | volume = 15 | issue = 8| pages = 695–710 | doi=10.1007/bf02235991| pmid = 5468838 | s2cid = 2140863 }}</ref><ref>Cavalli-Sforza, L., P. Menozzi and A. Piazza.  1994. ''The history and geography of human genes''  Princeton: Princeton University Press</ref><ref>{{cite journal | last1 = Holden | first1 = C. | last2 = Mace | first2 = R. | year = 1997 | title = Phylogenetic analysis of the evolution of lactose digestion in adults | journal = Human Biology | volume = 69 | issue = 5| pages = 605–628 | pmid = 9299882 }}</ref><ref>Durham, W.  1991.  '' Coevolution: Genes, culture and human diversity''.  Stanford: Stanford University Press.  Chapter 5</ref><ref>Perry, G., N. Dominy, K. Claw, A. Lee, H> Fiegler, R. Redon, J. Werner, F. Villanea, J. Mountain, R. Misra, N. Carter, C. Lee, A. Stone. Diet and the evolution of human amylase gene copy number variation.  ''Nature Genetics'' 39:1256-1260.</ref>  As another example, it is likely that once culture became adaptive, genetic selection caused a refinement of the cognitive architecture that stores and transmits cultural information.  This refinement may have further influenced the way culture is stored and the biases that govern its transmission.

DIT also predicts that, under certain situations, cultural evolution may select for traits that are genetically maladaptive.  An example of this is the [[Finance:Demographic transition|demographic transition]], which describes the fall of birth rates within industrialized societies.  Dual inheritance theorists hypothesize that the demographic transition may be a result of a prestige bias, where individuals that forgo reproduction to gain more influence in industrial societies are more likely to be chosen as cultural models.<ref>Boyd, R. and P. J. Richerson.  1985. '' Culture and the Evolutionary Process''.  Chicago: University of Chicago Press. pp. 199-202.</ref><ref>Richerson, P. J. and R. Boyd.  2005. ''Not By Genes Alone: How Culture Transformed Human Evolution''.  Chicago: University of Chicago Press. pp. 169-182.</ref>

==View of culture==

People have defined the word "culture" to describe a large set of different phenomena.<ref>Kroeberm A. and C. Kluckhohn.  1952. ''Culture; A Critical Review of Concepts and Definitions.''  Cambridge, MA: Harvard University.</ref><ref>Fox, R. and B. King.  2002. ''Anthropology Beyond Culture'' Oxford: Berg.</ref>  A definition that sums up what is meant by "culture" in DIT is:

{{Quotation|Culture is socially learned information stored in individuals' brains that is capable of affecting behavior.<ref>Richerson, P. and R. Boyd.  2005. ''Not By Genes Alone: How Culture Transformed Human Evolution'' Chicago: University of Chicago Press. pg 6.</ref><ref>Boyd, R. and P. Richerson. 2000. Memes: Universal Acid or a Better Mouse Trap? In R. Aunger, Ed. ''Darwinizing Culture: The Status of Memetics as a Science.'' Oxford: Oxford University Press. pp. 143-162. [https://web.archive.org/web/20000817023031/http://www.sscnet.ucla.edu/anthro/faculty/boyd/CambMeme.PDF Full text]</ref>}}

This view of culture emphasizes population thinking by focusing on the process by which culture is generated and maintained.  It also views culture as a dynamic property of individuals, as opposed to a view of culture as a superorganic entity to which individuals must conform.<ref>Richerson, P.J. and R. Boyd. 2001. Culture is Part of Human Biology: Why the Superorganic Concept Serves the Human Sciences Badly. In ''Science Studies: Probing the Dynamics of Scientific Knowledge'', In S. Maasen and M. Winterhager, Ed. Bielefeld: Verlag.[http://xcelab.net/rm/wp-content/uploads/2008/08/cultureisbiology.pdf]</ref> This view's main advantage is that it connects individual-level processes to population-level outcomes.<ref>Richerson, P. and R. Boyd.  2005. ''Not By Genes Alone: How Culture Transformed Human Evolution'' Chicago: University of Chicago Press. pg 7.</ref>

==Genetic influence on cultural evolution==

Genes affect cultural evolution via psychological predispositions on cultural learning.<ref>{{cite journal |doi=10.1080/1047840X.2013.764814 | volume=24 | title=Promise and Challenges Surrounding Culture–Gene Coevolution and Gene–Culture Interactions | year=2013 | journal=Psychological Inquiry | pages=64–70 | last1 = Sasaki | first1 = Joni Y.| s2cid=144039856 }}</ref>  Genes encode much of the information needed to form the human brain.  Genes constrain the brain's structure and, hence, the ability of the brain to acquire and store culture.  Genes may also endow individuals with certain types of transmission bias (described below).

==Cultural influences on genetic evolution==

Culture can profoundly influence gene frequencies in a population.

'''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=":0">{{Cite journal|last1=Itan|first1=Yuval|last2=Powell|first2=Adam|last3=Beaumont|first3=Mark A.|last4=Burger|first4=Joachim|last5=Thomas|first5=Mark G.|date=2009-08-28|title=The Origins of Lactase Persistence in Europe|journal=PLOS Computational Biology|volume=5|issue=8|pages=e1000491|doi=10.1371/journal.pcbi.1000491|issn=1553-7358| pmc=2722739 |pmid=19714206|bibcode=2009PLSCB...5E0491I |doi-access=free }}</ref>  lactase production stopped shortly after weaning,<ref>{{Cite journal|last1=Malmström|first1=Helena|last2=Linderholm|first2=Anna|last3=Lidén|first3=Kerstin|last4=Storå|first4=Jan|last5=Molnar|first5=Petra|last6=Holmlund|first6=Gunilla|last7=Jakobsson|first7=Mattias|last8=Götherström|first8=Anders|date=2010-01-01|title=High frequency of lactose intolerance in a prehistoric hunter-gatherer population in northern Europe|journal=BMC Evolutionary Biology|volume=10|pages=89|doi=10.1186/1471-2148-10-89|issn=1471-2148| pmc=2862036 |pmid=20353605 |doi-access=free }}</ref> and in societies which did not develop dairying, such as East Asians and Amerindians, this is still true today.<ref>{{Cite web|url=http://www.ucl.ac.uk/mace-lab/resources/glad/LP_maps|title=Maps|website=www.ucl.ac.uk|language=en|access-date=2017-03-27|archive-url=https://web.archive.org/web/20170328105300/http://www.ucl.ac.uk/mace-lab/resources/glad/LP_maps|archive-date=2017-03-28|url-status=dead}}</ref><ref>{{Cite journal|last1=Gerbault|first1=Pascale|last2=Roffet-Salque|first2=Mélanie|last3=Evershed|first3=Richard P.|last4=Thomas|first4=Mark G.|date=2013-12-01|title=How long have adult humans been consuming milk?|journal=IUBMB Life|language=en|volume=65|issue=12|pages=983–990|doi=10.1002/iub.1227|pmid=24339181|s2cid=34564411|issn=1521-6551|doi-access=free}}</ref> In areas with lactase persistence, it is believed that by domesticating animals, a source of milk became available while an adult and thus strong selection for lactase persistence could occur,<ref name=":0" /><ref name=":1">{{Cite journal|last1=Bersaglieri|first1=Todd|last2=Sabeti|first2=Pardis C.|last3=Patterson|first3=Nick|last4=Vanderploeg|first4=Trisha|last5=Schaffner|first5=Steve F.|last6=Drake|first6=Jared A.|last7=Rhodes|first7=Matthew|last8=Reich|first8=David E.|last9=Hirschhorn|first9=Joel N.|date=2017-03-27|title=Genetic Signatures of Strong Recent Positive Selection at the Lactase Gene|journal=American Journal of Human Genetics|volume=74|issue=6|pages=1111–1120|doi=10.1086/421051|issn=0002-9297| pmc=1182075 |pmid=15114531}}</ref> in a Scandinavian population the estimated [[Biology:Selection coefficient|selection coefficient]] was 0.09-0.19.<ref name=":1" /> This implies that the cultural practice of raising cattle first for meat and later for milk led to selection for genetic traits for lactose digestion.<ref>Laland, K. N. and G. R. Brown.  2002.  ''Sense & Nonsense: Evolutionary Perspectives on Human Behavior.''  Oxford: Oxford University Press. p. 260</ref>  Recently, analysis of natural selection on the human genome suggests that civilization has accelerated genetic change in humans over the past 10,000 years.<ref>Cochran, G. and H. Harpending. 2009.  ''The 10,000 Year Explosion: How Civilization Accelerated Human Evolution.'' Basic Books.</ref>

'''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|date=2012-11-06|title=Metabolic constraint imposes tradeoff between body size and number of brain neurons in human evolution|journal=Proceedings of the National Academy of Sciences|language=en|volume=109|issue=45|pages=18571–18576|doi=10.1073/pnas.1206390109|issn=0027-8424| pmc=3494886 |pmid=23090991|bibcode=2012PNAS..10918571F|doi-access=free}}</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|last=Farrell|first=J. H.|date=1956-05-01|title=The effect on digestibility of methods commonly used to increase the tenderness of lean meat|journal=British Journal of Nutrition|volume=10|issue=2|pages=111–115|doi=10.1079/BJN19560019|pmid=13315930|issn=1475-2662|doi-access=free}}</ref><ref>{{Cite book|title=The Secret of Our Success: How Culture Is Driving Human Evolution, Domesticating Our Species, and Making Us Smarter|last=Henrich|first=Joseph|publisher=Princeton University Press|year=2015|isbn=9780691166858|location=Princeton|pages=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.<ref name=":3">{{Cite book|title=Catching Fire How Cooking Made Us Human|last=Wrangham|first=Richard|publisher=Profile Books|year=2009|isbn=9781846682865|location=London|pages=40}}</ref> 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=":8">{{Cite journal|last1=Carmody|first1=Rachel N.|last2=Wrangham|first2=Richard W.|date=2009-10-01|title=The energetic significance of cooking|journal=Journal of Human Evolution|volume=57|issue=4|pages=379–391|doi=10.1016/j.jhevol.2009.02.011|issn=1095-8606|pmid=19732938|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.|date=2011-11-29|title=Energetic consequences of thermal and nonthermal food processing|journal=Proceedings of the National Academy of Sciences of the United States of America|volume=108|issue=48|pages=19199–19203|doi=10.1073/pnas.1112128108|issn=1091-6490| 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.<ref>{{Cite book|url=https://www.amazon.co.uk/dp/B003F5NSVK/ref=dp-kindle-redirect?_encoding=UTF8&btkr=1|title=Catching Fire: How Cooking Made Us Human|last=Wrangham|first=Richard|date=2010-08-06|publisher=Profile Books|edition=Main|pages=140|language=en}}</ref> 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.<ref>{{Cite book|title=Catching Fire: How Cooking Made Us Human|last=Wrangham|first=Richard|date=2010-05-27|publisher=Profile Books|isbn=9781846682865|edition=Main|location=London|pages=142|language=en}}</ref> Digestibility of cooked carbohydrates is approximately on average 30% higher than digestibility of non-cooked carbohydrates.<ref name=":8" /><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=":5">{{Cite journal|last1=Koebnick|first1=C.|last2=Strassner|first2=C.|last3=Hoffmann|first3=I.|last4=Leitzmann|first4=C.|date=1999-01-01|title=Consequences of a long-term raw food diet on body weight and menstruation: results of a questionnaire survey|journal=Annals of Nutrition & Metabolism|volume=43|issue=2|pages=69–79|doi=10.1159/000012770|issn=0250-6807|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=":5" /> This is despite access to many non-thermal processing, like grinding, pounding or heating to 48&nbsp;°C. (118&nbsp;°F).<ref name=":5" /> With approximately 86 billion neurons in the human brain and 60–70&nbsp;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=":6" /> 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=":6">{{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.|date=2016-04-25|title=Human Brain Expansion during Evolution Is Independent of Fire Control and Cooking|journal=Frontiers in Neuroscience|volume=10|pages=167|doi=10.3389/fnins.2016.00167|issn=1662-4548| 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.|date=2016-03-24|title=Impact of meat and Lower Palaeolithic food processing techniques on chewing in humans|journal=Nature|language=en|volume=531|issue=7595|pages=500–503|doi=10.1038/nature16990|pmid=26958832|issn=0028-0836|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=":6" /> 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=":6" /><ref>{{Cite journal|last1=Roebroeks|first1=Wil|last2=Villa|first2=Paola|date=2011-03-29|title=On the earliest evidence for habitual use of fire in Europe|journal=Proceedings of the National Academy of Sciences of the United States of America|volume=108|issue=13|pages=5209–5214|doi=10.1073/pnas.1018116108|issn=0027-8424| pmc=3069174 |pmid=21402905|bibcode=2011PNAS..108.5209R|doi-access=free}}</ref> Wrangham argues that anatomical evidence around the time of the origin of ''[[Biology:Homo erectus|Homo erectus]]'' (1.8 million years ago), indicates that the control of fire and hence cooking occurred.<ref name=":8" /> 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.<ref>{{Cite book|title=Catching Fire: How Cooking Made Us Human|last=Wrangham|first=Richard|date=2010-05-27|publisher=Profile Books|isbn=9781846682865|edition=Main|location=London|pages=98–102|language=en}}</ref> 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.<ref>{{Cite book|url=https://www.amazon.co.uk/dp/B003F5NSVK/ref=dp-kindle-redirect?_encoding=UTF8&btkr=1|title=Catching Fire: How Cooking Made Us Human|last=Wrangham|first=Richard|date=2010-08-06|publisher=Profile Books|edition=Main|pages=127|language=en}}</ref> This positive feedback loop is argued to have led to the rapid brain size increases seen in the ''Homo'' lineage.<ref>{{Cite book|title=Catching Fire: How Cooking Made Us Human|last=Wrangham|first=Richard|date=2010-05-27|publisher=Profile Books|isbn=9781846682865|edition=Main|location=London|pages=127|language=en}}</ref><ref name=":6" />

==Mechanisms of cultural evolution==

In DIT, the evolution and maintenance of cultures is described by five major mechanisms: natural selection of cultural variants, random variation, cultural drift, guided variation and transmission bias.

===Natural selection===
Cultural differences among individuals can lead to differential survival of individuals. The patterns of this selective process depend on transmission biases and can result in behavior that is more adaptive to a given environment.

===Random variation===
Random variation arises from errors in the learning, display or recall of cultural information, and is roughly analogous to the process of [[Biology:Mutation|mutation]] in genetic evolution.

===Cultural drift===
Cultural drift is a process roughly analogous to [[Biology:Genetic drift|genetic drift]] in evolutionary biology.<ref>{{cite journal | last1 = Koerper | first1 = H. | last2 = Stickel | first2 = E. | year = 1980 | title = Cultural Drift: A Primary Process of Culture Change | journal = Journal of Anthropological Research | volume = 36 | issue = 4| pages = 463–469 | doi = 10.1086/jar.36.4.3629615 | s2cid = 163932368 }}</ref><ref name="CavalliSfornza">Cavalli-Sfornza, L. and M. Feldman. 1981.  ''Cultural Transmission and Evolution: A Quantitative Approach''.  Princeton, New Jersey: Princeton University Press.</ref><ref name="artsci.wustl">{{cite journal | last1 = Bentley | first1 = R.A. | last2 = Hahn | first2 = M.W. | last3 = Shennan | first3 = S.J. | year = 2004 | title = Random drift and culture change | url = http://artsci.wustl.edu/~pboyer/CEwebsite/Archive/ShennanRandomDrift.pdf | journal = Proceedings of the Royal Society B | volume = 271 | issue = 1547 | pages = 1443–1450 | doi = 10.1098/rspb.2004.2746 | pmid = 15306315 | pmc = 1691747 | access-date = 2008-05-05 | archive-url = https://web.archive.org/web/20110928021713/http://artsci.wustl.edu/~pboyer/CEwebsite/Archive/ShennanRandomDrift.pdf | archive-date = 2011-09-28 | url-status = dead }}</ref>  In cultural drift, the frequency of cultural traits in a population may be subject to random fluctuations due to chance variations in which traits are observed and transmitted (sometimes called "sampling error").<ref name="duke">{{cite journal | last1 = Hahn | first1 = M.W. | last2 = Bentley | first2 = R. A. | year = 2003 | title = Drift as a mechanism for cultural change: An example from baby names | url = http://www.duke.edu/~mwh3/BabyNames.pdf | journal = Proceedings of the Royal Society B | volume = 270 | issue = Suppl 1 | pages = S120–S123 |doi=10.1098/rsbl.2003.0045 | pmid=12952655 | pmc=1698036}}</ref> These fluctuations might cause cultural variants to disappear from a population.  This effect should be especially strong in small populations.<ref>Boyd, R. and P. J. Richerson.  1985. '' Culture and the Evolutionary Process''.  Chicago: University of Chicago Press. pp.9, 69</ref> A model by Hahn and Bentley shows that cultural drift gives a reasonably good approximation to changes in the popularity of American baby names.<ref name="duke" /> Drift processes have also been suggested to explain changes in archaeological pottery and technology patent applications.<ref name="artsci.wustl" />  Changes in the songs of song birds are also thought to arise from drift processes, where distinct dialects in different groups occur due to errors in songbird singing and acquisition by successive generations.<ref>P.J.B. Slater, V.M. Janik.  Vocal Learning.  In "Encyclopedia of Animal Behavior", 2010, Pages 551-557.  http://www.sciencedirect.com/science/referenceworks/9780080453378</ref>  Cultural drift is also observed in an early computer model of cultural evolution.<ref>Gabora, L. (1995). [http://www.vub.ac.be/CLEA/liane/papers/mav.htm Meme and variations: A computer model of cultural evolution]. In (L. Nadel & D. Stein, Eds.) ''1993 Lectures in Complex Systems'', Addison-Wesley, 471-486.</ref>

===Guided variation===

Cultural traits may be gained in a population through the process of individual learning.  Once an individual learns a novel trait, it can be transmitted to other members of the population.  The process of guided variation depends on an adaptive standard that determines what cultural variants are learned.

===Biased transmission===

Understanding the different ways that culture traits can be transmitted between individuals has been an important part of DIT research since the 1970s.<ref>{{cite journal | last1 = Feldman | first1 = M. |  last2 = Cavalli-Sforza | first2 = L. | year = 1976 | title = Cultural and biological evolutionary processes, selection for a trait under complex transmission | journal = Theoretical Population Biology | volume = 9 | issue = 2| pages = 238–259 | doi=10.1016/0040-5809(76)90047-2 | pmid=1273802}}</ref><ref>{{cite journal | last1 = Feldman | first1 = M | last2 = Cavalli-Sfornza | first2 = L. | year = 1977 | title = The evolution of continuous variation: II, complex transmission and assortive mating | journal = Theoretical Population Biology | volume = 11 | issue = 2| pages = 161–181 | doi=10.1016/0040-5809(77)90024-7| pmid = 867286 }}</ref>  Transmission biases occur when some cultural variants are favored over others during the process of cultural transmission.<ref name="Boyd">Boyd, R., and P. Richerson. 1985. ''Culture and the Evolutionary Process''. Chicago: The University of Chicago Press.</ref>  Boyd and Richerson (1985)<ref name="Boyd" /> defined and analytically modeled a number of possible transmission biases.  The list of biases has been refined over the years, especially by Henrich and McElreath.<ref>{{cite journal|last1=Henrich|first1=J.|last2=McElreath|first2=R.|year=2003|title=The Evolution of Cultural Evolution|journal=Evolutionary Anthropology|volume=12|issue=3|pages=123–135|url=http://www.anthro.ucdavis.edu/mcelreath/henrich%20mcelreath%20EA%202003.pdf#search='dual%20inheritance%20theorypdf'|doi=10.1002/evan.10110|s2cid=14302229|access-date=2009-09-08|archive-url=https://web.archive.org/web/20050528024700/http://www.anthro.ucdavis.edu/mcelreath/henrich%20mcelreath%20EA%202003.pdf#search='dual%20inheritance%20theorypdf'|archive-date=2005-05-28|url-status=dead}}</ref>

====Content bias====

Content biases result from situations where some aspect of a cultural variant's content makes them more likely to be adopted.<ref name="Henrich">Henrich, J. and R. McElreath. 2007. Dual inheritance theory: the evolution of human cultural capacities and cultural evolution. Oxford Handbook of Evolutionary Psychology, R. Dunbar and L. Barrett, eds., Ch. 38. Oxford: Oxford University Press.</ref>  Content biases can result from genetic preferences, preferences determined by existing cultural traits, or a combination of the two.  For example, food preferences can result from genetic preferences for sugary or fatty foods and socially-learned eating practices and taboos.<ref name="Henrich" />  Content biases are sometimes called "direct biases."<ref name="Boyd" />

====Context bias====

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=====

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 = J. | last2 = McElreath | first2 = R. | year = 2003 | title = The evolution of cultural evolution | url = http://arbeit.ucdavis.edu/mcelreath/files/henrich%20mcelreath%20EA%202003.pdf | journal = Evolutionary Anthropology | volume = 12 | issue = 3 | pages = 123–135 | doi = 10.1002/evan.10110 | s2cid = 14302229 | access-date = 2008-03-27 | archive-url = https://web.archive.org/web/20080407082050/http://arbeit.ucdavis.edu/mcelreath/files/henrich%20mcelreath%20EA%202003.pdf | archive-date = 2008-04-07 | url-status = dead }}</ref> A "prestige bias" results when individuals are more likely to imitate cultural models that are seen as having more 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=====

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.

==Social learning and cumulative cultural evolution==

In DIT, the evolution of culture is dependent on the evolution of social learning.  Analytic models show that social learning becomes evolutionarily beneficial when the environment changes with enough frequency that genetic inheritance can not track the changes, but not fast enough that individual learning is more efficient.<ref>Richerson, P.J. and R. Boyd. 2000. Climate, culture, and the evolution of cognition. In C.M. Heyes and L. Huber, (Eds), ''The Evolution of Cognition.'' Massachusetts: MIT Press.</ref> For environments that have very little variability, social learning is not needed since genes can adapt fast enough to the changes that occur, and innate behaviour is able to deal with the constant environment.<ref>{{Cite journal|title=Carving the Cognitive Niche: Optimal Learning Strategies in Homogeneous and Heterogeneous Environments - ScienceDirect|journal=Journal of Theoretical Biology|volume=220|issue=2|pages=169–188|language=en|doi=10.1006/jtbi.2003.3146|year=2003|last1=Kerr|first1=Benjamin|last2=Feldman|first2=Marcus W.|pmid=12468290}}</ref> In fast changing environments cultural learning would not be useful because what the previous generation knew is now outdated and will provide no benefit in the changed environment, and hence individual learning is more beneficial. It is only in the moderately changing environment where cultural learning becomes useful since each generation shares a mostly similar environment but genes have insufficient time to change to changes in the environment.<ref name=":7" /> While other species have social learning, and thus some level of culture, only humans, some birds and chimpanzees are known to have cumulative culture.<ref>Tomasello, M. 1999.  ''The Cultural Origins of Human Cognition.'' Cambridge, Massachusetts: Cambridge University Press.</ref>  Boyd and Richerson argue that the evolution of cumulative culture depends on observational learning and is uncommon in other species because it is ineffective when it is rare in a population.  They propose that the environmental changes occurring in the [[Earth:Pleistocene|Pleistocene]] may have provided the right environmental conditions.<ref name=":7">{{cite book | last1 = Richerson | first1 = P. J. | last2 = Boyd | first2 = R. | title = Perspectives in Ethology | chapter = Built for Speed: Pleistocene Climate Variation and the Origin of Human Culture | year = 2000 | volume = 13 | pages = 1–45 | doi=10.1007/978-1-4615-1221-9_1| isbn = 978-1-4613-5447-5 }}</ref>  Michael Tomasello argues that cumulative cultural evolution results from a [[Ratchet effect|ratchet effect]] that began when humans developed the cognitive architecture to understand others as mental agents.<ref>Tomasello, M. 1999. ''The Cultural Origins of Human Cognition''. Cambridge, MA: Harvard University Press.</ref> Furthermore, Tomasello proposed in the 80s that there are some disparities between the observational learning mechanisms found in humans and great apes - which go some way to explain the observable difference between great ape traditions and human types of culture (see [[Biology:Emulation (observational learning)|Emulation (observational learning)]]).

==Cultural group selection==
{{details|topic=cultural group selection|Cultural group selection}}

Although [[Biology:Group selection|group selection]] is commonly thought to be nonexistent or unimportant in genetic evolution,<ref>[[Biography:George C. Williams (biologist)|Williams, G.C.]] 1972. ''Adaptation and Natural Selection: A Critique of Some Current Evolutionary Thought''. Princeton: Princeton University Press. {{ISBN|0-691-02357-3}}</ref><ref>[[Biography:George C. Williams (biologist)|Williams, G.C.]] 1986. ''Evolution Through Group Selection.'' Blackwell. {{ISBN|0-632-01541-1}}</ref><ref>{{cite journal | last1 = Maynard Smith | first1 = J. |  year = 1964 | title = Group selection and kin selection  | journal = Nature | volume = 201 | issue = 4924| pages = 1145–1147 | doi=10.1038/2011145a0 | bibcode=1964Natur.201.1145S| s2cid = 4177102 }}</ref> DIT predicts that, due to the nature of cultural inheritance, it may be an important force in cultural evolution.  Group selection occurs in cultural evolution because conformist biases make it difficult for novel cultural traits to spread through a population (see above section on transmission biases). Conformist bias also helps maintain variation between groups.  These two properties, rare in genetic transmission, are necessary for group selection to operate.<ref>{{cite journal | last1 = Uyenoyama | first1 = M. | last2 = Feldman | first2 = M. W. | year = 1980 | title = Theories of kin and group selection: a population genetics perspective | journal = Theoretical Population Biology | volume = 17 | issue = 3| pages = 380–414 | doi=10.1016/0040-5809(80)90033-7| pmid = 7434256 }}</ref>  Based on an earlier model by Cavalli-Sforza and Feldman,<ref>{{cite journal | last1 = Cavalli-Sforza | first1 = L. L. | last2 = Feldman | first2 = M. W. | year = 1973 | title = Models for cultural inheritance. I. Group mean and within group variation | journal = Theoretical Population Biology | volume = 4 | issue = 1| pages = 42–44 | doi=10.1016/0040-5809(73)90005-1| pmid = 4726009 }}</ref> Boyd and Richerson show that conformist biases are almost inevitable when traits spread through social learning,<ref>Boyd, R. and P. J. Richerson.  1985. '' Culture and the Evolutionary Process''.  Chicago: University of Chicago Press. pg. 227–240.</ref> implying that group selection is common in cultural evolution.  Analysis of small groups in New Guinea imply that cultural group selection might be a good explanation for slowly changing aspects of social structure, but not for rapidly changing fads.<ref name="Soltis">{{cite journal | last1 = Soltis | first1 = J. | last2 = Boyd | first2 = R. | last3 = Richerson | first3 = P. J. | year = 1995 | title = Can group-functional behaviors evolve by cultural group selection? An empirical test | url = http://www.des.ucdavis.edu/faculty/richerson/SoltisBoydRichersonCA95.pdf | journal = Current Anthropology | volume = 36 | issue = 3| pages = 473–494 | doi=10.1086/204381| s2cid = 43998139 }}</ref>  The ability of cultural evolution to maintain intergroup diversity is what allows for the study of cultural phylogenetics.<ref>Mace, R., C. Holden, and S. Shennan (Eds.) 2005.  ''The evolution of cultural diversity: a phylogenetic approach. '' London:University College London Press.</ref>

==Historical development==

In 1876, [[Biography:Friedrich Engels|Friedrich Engels]] wrote a manuscript titled The Part Played by Labour in the Transition from Ape to Man, accredited as a founding document of DIH;<ref>{{Cite book |last=Foster |first=John |title=Marx’s Ecology: Materialism and Nature |publisher=Monthly Review Press |year=2000 |isbn=9781583670125 |location=New York |pages=203}}</ref> “The approach to gene-culture coevolution first developed by Engels and developed later on by anthropologists…” is described by [[Biography:Stephen Jay Gould|Stephen Jay Gould]] as “…the best nineteenth-century case for gene-culture coevolution.”<ref>{{Cite book |last=Gould |first=Stephen |title=An Urchin in the Storm |publisher=W.W. Norton |year=1987 |isbn=0-393-02492-X |location=New York |pages=111-112}}</ref> The idea that human cultures undergo a similar evolutionary process as genetic evolution also goes back to [[Biography:Charles Darwin|Darwin]].<ref>Darwin, C.  1874. ''The descent of man and selection in relation to sex.'' 2nd ed. 2 vols. New York: American Home Library.</ref> In the 1960s, Donald T. Campbell published some of the first theoretical work that adapted principles of evolutionary theory to the evolution of cultures.<ref>Campbell, D. 1965.  Variation and selective retention in socio-cultural evolution.  In ''Social change in developing areas: A reinterpretation of evolutionary theory'', ed. H. Barringer, G. Blanksten, and R. Mack, 19-49.  Cambridge, MA: Schenkman Publishing Company.</ref> In 1976, two developments in cultural evolutionary theory set the stage for DIT. In that year [[Biography:Richard Dawkins|Richard Dawkins's]] ''[[Biology:The Selfish Gene|The Selfish Gene]]'' introduced ideas of cultural evolution to a popular audience.  Although one of the best-selling science books of all time, because of its lack of mathematical rigor, it had little effect on the development of DIT. Also in 1976, geneticists [[Biography:Marcus Feldman|Marcus Feldman]] and [[Biography:Luigi Luca Cavalli-Sforza|Luigi Luca Cavalli-Sforza]] published the first dynamic models of gene–culture coevolution.<ref>{{cite journal | last1 = Feldman | first1 = M. | last2 = Cavalli-Sforna | first2 = L. | year = 1976 | title = Cultural and biological evolutionary processes, selection for a trait under complex transmission | journal = Theoretical Population Biology | volume = 9 | issue = 2| pages = 238–59 | doi=10.1016/0040-5809(76)90047-2 | pmid=1273802}}</ref>  These models were to form the basis for subsequent work on DIT, heralded by the publication of three seminal books in the 1980s.

The first was Charles Lumsden and [[Biography:E. O. Wilson|E.O. Wilson's]] ''Genes, Mind and Culture''.<ref>Lumsden C., and E. Wilson.  1981.  ''Genes, Mind and Culture: The Coevolutionary Process.''  Cambridge, MA: Harvard University Press.</ref>  This book outlined a series of mathematical models of how genetic evolution might favor the selection of cultural traits and how cultural traits might, in turn, affect the speed of genetic evolution.  While it was the first book published describing how genes and culture might coevolve, it had relatively little effect on the further development of DIT.<ref name="Laland">Laland K. and G. Brown. 2002. ''Sense and Nonsense: Evolutionary Perspectives on Human Behavior''. Oxford: Oxford University Press.</ref> Some critics felt that their models depended too heavily on genetic mechanisms at the expense of cultural mechanisms.<ref>{{cite journal | last1 = Boyd | first1 = R. | last2 = Richerson | first2 = P. | year = 1983 | title = The cultural transmission of acquired variation: effects on genetic fitness | journal = Journal of Theoretical Biology | volume = 100 | issue = 4| pages = 567–96 | doi=10.1016/0022-5193(83)90324-7| pmid = 6876815 | bibcode = 1983JThBi.100..567B }}</ref>  Controversy surrounding Wilson's [[Philosophy:Sociobiology#Controversy|sociobiological theories]] may also have decreased the lasting effect of this book.<ref name="Laland" />

The second 1981 book was [[Biography:Luigi Luca Cavalli-Sforza|Cavalli-Sforza]] and Feldman's ''Cultural Transmission and Evolution: A Quantitative Approach''.<ref name="CavalliSfornza" />  Borrowing heavily from [[Biology:Population genetics|population genetics]] and [[Social:Epidemiology|epidemiology]], this book built a mathematical theory concerning the spread of cultural traits. It describes the evolutionary implications of [[Biology:Vertical transmission|vertical transmission]], passing cultural traits from parents to offspring; oblique transmission, passing cultural traits from any member of an older generation to a younger generation; and [[Medicine:Horizontal transmission|horizontal transmission]], passing traits between members of the same population.

The next significant DIT publication was Robert Boyd and Peter Richerson's 1985 ''Culture and the Evolutionary Process''.<ref name="Boyd" /> This book presents the now-standard mathematical models of the evolution of social learning under different environmental conditions, the population effects of social learning, various forces of selection on cultural learning rules, different forms of biased transmission and their population-level effects, and conflicts between cultural and genetic evolution.  The book's conclusion also outlined areas for future research that are still relevant today.<ref>{{cite journal|last1=Marwick|first1=Ben|title=What Can Archaeology Do With Boyd and Richerson's Cultural Evolutionary Program?|journal=Review of Archaeology|date=2005|volume=26|issue=2|pages=30–40|hdl=1885/44496}}</ref>

==Current and future research==

In their 1985 book, Boyd and Richerson outlined an agenda for future DIT research. This agenda, outlined below, called for the development of both theoretical models and empirical research. DIT has since built a rich tradition of theoretical models over the past two decades.<ref>Boyd, R. and P. J. Richerson. 2005. ''The Origin and Evolution of Cultures''. Oxford: Oxford University Press. pp. 294-299.</ref> However, there has not been a comparable level of empirical work.

In a 2006 interview Harvard biologist [[Biography:E. O. Wilson|E. O. Wilson]] expressed disappointment at the little attention afforded to DIT:

{{Quotation|"...for some reason I haven't fully fathomed, this most promising frontier of scientific research has attracted very few people and very little effort."<ref>{{cite journal | last1 = Haag | first1 = Allison | year = 2006 | title = The synthesizer | url = http://seedmagazine.com/news/2007/01/the_synthesizer.php | archive-url = https://web.archive.org/web/20070210064034/http://www.seedmagazine.com/news/2007/01/the_synthesizer.php | url-status = unfit | archive-date = 2007-02-10 | journal = SEED | volume = 2 | issue = 7| page = 46 }}</ref>}}

[[Biography:Kevin Laland|Kevin Laland]] and [[Biography:Gillian Ruth Brown|Gillian Ruth Brown]] attribute this lack of attention to DIT's heavy reliance on formal modeling.

{{Quotation|"In many ways the most complex and potentially rewarding of all approaches, [DIT], with its multiple processes and cerebral onslaught of sigmas and deltas, may appear too abstract to all but the most enthusiastic reader. Until such a time as the theoretical hieroglyphics can be translated into a respectable empirical science most observers will remain immune to its message."<ref>Laland, K. N. and G. R. Brown. 2002. ''Sense & Nonsense: Evolutionary Perspectives on Human Behavior.'' Oxford: Oxford University Press. p. 290.</ref>}}

Economist [[Biography:Herbert Gintis|Herbert Gintis]] disagrees with this critique, citing empirical work as well as more recent work using techniques from [[Finance:Behavioral economics|behavioral economics]].<ref>Herb Gintis Amazon.com review: https://www.amazon.com/review/product/0198508840/</ref> These behavioral economic techniques have been adapted to test predictions of cultural evolutionary models in laboratory settings<ref>McElreath, R., M. Lubell, P. J. Richerson, T. M. Waring, W. Baum, E. Edsten, C. Efferson, and B. Paciotti. 2005. [http://www.des.ucdavis.edu/faculty/Richerson/WheatPotatoes.pdf Applying formal models to the laboratory study of social learning: The effect of task difficulty and environmental fluctuation.] Evolution and Human Behavior 26: 483-508.</ref><ref>{{cite journal |author=Efferson, C. |author2=R. Lalive |author3=P. J. Richerson |author4=R. McElreath |author5=M. Lubell |year=2008 |title=Conformists and mavericks: the empirics of frequency-dependent cultural transmission |journal=Evolution and Human Behavior |volume=29 |issue=1 |pages=56–64 |doi=10.1016/j.evolhumbehav.2007.08.003|citeseerx=10.1.1.606.1789 |s2cid=2107499 }}</ref><ref>{{cite journal | last1 = Baum | first1 = W. M. | last2 = Richerson | first2 = P. J. | last3 = Efferson | first3 = C. M. | last4 = Paciotti | first4 = B. M. | year = 2004 | title = Cultural evolution in laboratory micro-societies including traditions of rule-giving and rule-following | url = http://www.des.ucdavis.edu/faculty/Richerson/Baumetalprinted.pdf | journal = Evolution and Human Behavior | volume = 25 | issue = 5| pages = 305–326 | doi=10.1016/j.evolhumbehav.2004.05.003| citeseerx = 10.1.1.404.8710 }}</ref> as well as studying differences in cooperation in fifteen small-scale societies in the field.<ref name="Henrich_a">Henrich, J., R. Boyd, S. Bowles, C. Camerer, E. Fehr, H. Gintis (Eds). 2004. ''Foundations of Human Sociality: Economic Experiments and Ethnographic Evidence from Fifteen Small-Scale Societies'' Oxford: Oxford University Press.</ref>

Since one of the goals of DIT is to explain the distribution of human cultural traits, [[Social:Ethnography|ethnographic]] and [[Social:Ethnology|ethnologic]] techniques may also be useful for testing hypothesis stemming from DIT. Although findings from traditional ethnologic studies have been used to buttress DIT arguments,<ref>Cavalli-Sfornza, L. L. and M. Feldman. 1981. ''Cultural Transmission and Evolution: A Quantitative Approach.'' Princeton, New Jersey: Princeton University Press.</ref><ref>Boyd, R. and P. J. Richerson. 1985. '' Culture and the Evolutionary Process''. Chicago: University of Chicago Press.</ref> thus far there have been little ethnographic fieldwork designed to explicitly test these hypotheses.<ref name="Soltis" /><ref name="Henrich_a" /><ref>{{cite journal | last1 = McElreath | first1 = R | year = 2004 | title = Social learning and the maintenance of cultural variation: An evolutionary model and data from East Africa | url = http://arbeit.ucdavis.edu/mcelreath/files/mcelreath%20AA%202004.pdf | journal = American Anthropologist | volume = 106 | issue = 2 | pages = 308–321 | doi = 10.1525/aa.2004.106.2.308 | access-date = 2008-03-27 | archive-url = https://web.archive.org/web/20070717022400/http://arbeit.ucdavis.edu/mcelreath/files/mcelreath%20AA%202004.pdf | archive-date = 2007-07-17 | url-status = dead }}</ref>

Herb Gintis has named DIT one of the two major conceptual theories with potential for unifying the behavioral sciences, including economics, biology, anthropology, sociology, psychology and political science. Because it addresses both the genetic and cultural components of human inheritance, Gintis sees DIT models as providing the best explanations for the ultimate cause of human behavior and the best paradigm for integrating those disciplines with evolutionary theory.<ref>{{cite journal | last1 = Gintis | first1 = H | year = 2006 | title = A framework for the integration of the behavioral sciences | url = http://www.umass.edu/preferen/gintis/Unity-BBS%20Print%20Version.pdf| journal = Behavioral and Brain Sciences | volume = 30 | issue = 1| pages = 1–61 | doi=10.1017/s0140525x07000581| pmid = 17475022 | s2cid = 18887154 }}</ref> In a review of competing evolutionary perspectives on human behavior, Laland and Brown see DIT as the best candidate for uniting the other evolutionary perspectives under one theoretical umbrella.<ref name="Laland_a">Laland, K. N. and G. R. Brown.  2002.  ''Sense & Nonsense: Evolutionary Perspectives on Human Behavior.''  Oxford: Oxford University Press. p. 287-319.</ref>

==Relation to other fields==

===Sociology and cultural anthropology===

Two major topics of study in both sociology and [[Social:Cultural anthropology|cultural anthropology]] are human cultures and cultural variation.
However, Dual Inheritance theorists charge that both disciplines too often treat culture as a static superorganic entity that dictates human behavior.<ref name="Richerson">Richerson, P. and R. Boyd. 2001. [http://www.des.ucdavis.edu/faculty/Richerson/CultureIsBiology.pdf Culture is part of human biology: Why the superorganic concept serves the human sciences badly]. In M. Goodman and A. S. Moffat(Eds.) ''Probing Human Origins.'' Cambridge, Massachusetts: The American Academy of Arts & Sciences.</ref><ref>{{cite journal | last1 = Gintis | first1 = H | year = 2007 | title = A framework for the unification of the behavioral sciences | url = http://www.umass.edu/preferen/gintis/Unity-BBS%20Print%20Version.pdf | journal = Behavioral and Brain Sciences | volume = 30 | issue = 1| pages = 1–61 | doi=10.1017/s0140525x07000581| pmid = 17475022 | s2cid = 18887154 }}</ref> Cultures are defined by a suite of common traits shared by a large group of people. DIT theorists argue that this doesn't sufficiently explain variation in cultural traits at the individual level.  By contrast, DIT models human culture at the individual level and views culture as the result of a dynamic evolutionary process at the population level.<ref name="Richerson" /><ref>Richerson, P. J. and R. Boyd.  2005. ''Not By Genes Alone: How Culture Transformed Human Evolution''.  Chicago: University of Chicago Press. pg. 5-8</ref>

===Human sociobiology and evolutionary psychology===

Evolutionary psychologists study the evolved architecture of the human mind. They see it as composed of many different programs that process information, each with assumptions and procedures that were specialized by natural selection to solve a different adaptive problem faced by our hunter-gatherer ancestors (e.g., choosing mates, hunting, avoiding predators, cooperating, using aggression).<ref>Barkow, J., Cosmides, L, & Tooby, J. (1992) The Adapted Mind: Evolutionary Psychology and the Generation of Culture. Oxford University Press.</ref> These evolved programs contain content-rich assumptions about how the world and other people work. When ideas are passed from mind to mind, they are changed by these evolved inference systems (much like messages get changed in a game of telephone). But the changes are not usually random. Evolved programs add and subtract information, reshaping the ideas in ways that make them more "intuitive", more memorable, and more attention-grabbing. In other words, "memes" (ideas) are not precisely like genes. Genes are normally copied faithfully as they are replicated, but ideas normally are not. It's not just that ideas mutate every once in a while, like genes do. Ideas are transformed every time they are passed from mind to mind, because the sender's message is being interpreted by evolved inference systems in the receiver.<ref>Boyer, P. (2001) Religion Explained: The Evolutionary Origins of Religious Thought. Basic Books.</ref><ref>Sperber, D. (1996). Explaining Culture: A Naturalistic Approach. Blackwell.</ref> It is useful for some applications to note, however, that there are ways to pass ideas which are more resilient and involve substantially less mutation, such as by mass distribution of printed media. 

There is no necessary contradiction between evolutionary psychology and DIT, but evolutionary psychologists argue that the psychology implicit in many DIT models is too simple; evolved programs have a rich inferential structure not captured by the idea of a "content bias". They also argue that some of the phenomena DIT models attribute to cultural evolution are cases of "evoked culture"—situations in which different evolved programs are activated in different places, in response to cues in the environment.<ref>Tooby, J. & Cosmides, L., (1992) Psychological foundations of culture. In The Adapted Mind.</ref>

[[Philosophy:Sociobiology|Sociobiologists]] try to understand how maximizing genetic fitness, in either the modern era or past environments, can explain human behavior. When faced with a trait that seems maladaptive, some sociobiologists try to determine how the trait actually increases genetic fitness (maybe through kin selection or by speculating about early evolutionary environments).  Dual inheritance theorists, in contrast, will consider a variety of genetic and cultural processes in addition to natural selection on genes.

===Human behavioral ecology===

[[Biology:Human behavioral ecology|Human behavioral ecology]] (HBE) and DIT have a similar relationship to what ecology and evolutionary biology have in the biological sciences.  HBE is more concerned about ecological process and DIT more focused on historical process.<ref>{{cite journal|last1=Marwick|first1=Ben|title=Three styles of Darwinian evolution in the analysis of stone artefacts: Which one to use in mainland Southeast Asia?|journal=Australian Archaeology|date=2008|volume=67|issue=1|pages=79–86|doi=10.1080/03122417.2008.11681880|jstor=40288025|s2cid=15023222}}</ref>  One difference is that human behavioral ecologists often assume that culture is a system that produces the most adaptive outcome in a given environment.  This implies that similar behavioral traditions should be found in similar environments.  However, this is not always the case.  A study of African cultures showed that cultural history was a better predictor of cultural traits than local ecological conditions.<ref>{{cite journal | last1 = Guglielmino | first1 = C. R. | last2 = Viganotti | first2 = C. | last3 = Hewlett | first3 = B. | last4 = Cavalli-Sforza | first4 = L.L. | year = 1995 | title = Cultural variation in Africa: role of mechanism of transmission and adaptation | journal = Proceedings of the National Academy of Sciences USA | volume = 92 | issue = 16| pages = 7585–7589 | doi=10.1073/pnas.92.16.7585| pmid = 11607569 | pmc = 41384 | bibcode = 1995PNAS...92.7585G | doi-access = free }}</ref>

===Memetics===

[[Philosophy:Memetics|Memetics]], which comes from the [[Philosophy:Meme|meme]] idea described in [[Biography:Richard Dawkins|Dawkins's]] ''[[Biology:The Selfish Gene|The Selfish Gene]]'', is similar to DIT in that it treats culture as an evolutionary process that is distinct from genetic transmission.  However, there are some philosophical differences between memetics and DIT.<ref>Boyd, R. and P.J. Richerson. 2000. [http://www.des.ucdavis.edu/faculty/Richerson/CambMeme.PDF Memes: universal acid or better mouse trap].  In R. Aunger (Ed), ''Darwinizing Culture: The Status of Memetics as a Science''. Oxford: Oxford University Press. pp. 143–162.</ref>   One difference is that memetics' focus is on the selection potential of discrete replicators (memes), where DIT allows for transmission of both non-replicators and non-discrete cultural variants.  DIT does not assume that replicators are necessary for cumulative adaptive evolution. DIT also more strongly emphasizes the role of genetic inheritance in shaping the capacity for cultural evolution.  But perhaps the biggest difference is a difference in academic lineage. [[Philosophy:Memetics|Memetics]] as a label is more influential in popular culture than in academia. Critics of memetics argue that it is lacking in empirical support or is conceptually ill-founded, and question whether there is hope for the memetic research program succeeding. Proponents point out that many cultural traits are discrete, and that many existing models of cultural inheritance assume discrete cultural units, and hence involve memes.<ref>Laland, K. N. and G. R. Brown.  2002.  ''Sense & Nonsense: Evolutionary Perspectives on Human Behavior.''  Oxford: Oxford University Press. pp. 289-290.</ref>

==Shortcomings and criticisms==

Psychologist Liane Gabora has criticised DIT.<ref>{{cite journal | last1 = Gabora | first1 = L | year = 2008 | title = The cultural evolution of socially situated cognition | url = http://www.vub.ac.be/CLEA/liane/papers/ssc.htm | journal = Cognitive Systems Research | volume = 9 | issue = 1–2| pages = 104–113 | doi=10.1016/j.cogsys.2007.05.004| arxiv = 0803.2568 | bibcode = 2008arXiv0803.2568G | hdl = 2429/64746 | s2cid = 13592511 }}</ref><ref>{{cite journal | last1 = Gabora | first1 = L | year = 2011 | title = Five clarifications about cultural evolution | url = https://people.ok.ubc.ca/lgabora/papers/gabora-five-JOCC2011.pdf | journal = Journal of Cognition and Culture | volume = 11 | issue = 1–2| pages = 61–83 | doi=10.1163/156853711x568699| arxiv = 1309.2622 | hdl = 2429/64743 | s2cid = 4468795 }}</ref><ref>Gabora, L. (2011).  [http://www.psychologytoday.com/blog/mindbloggling/201105/how-generation-was-misled-about-natural-selection How a generation was misled about natural selection]. ''Psychology Today'', Mindbloggling.</ref> She argues that use of the term ‘dual inheritance’ to refer to not just traits that are transmitted by way of a self-assembly code (as in genetic evolution) but also traits that are ''not'' transmitted by way of a self-assembly code (as in cultural evolution) is misleading, because this second use does not capture the algorithmic structure that makes an inheritance system require a particular kind of mathematical framework.<ref>{{cite journal | last1 = Gabora | first1 = L | year = 2013 | title = An evolutionary framework for culture: Selectionism versus communal exchange. | journal = Physics of Life Reviews | volume = 10 | issue = 2| pages = 117–145 | doi=10.1016/j.plrev.2013.03.006 | pmid = 23623043 | arxiv = 1206.4386 | s2cid = 11208336 }}</ref>

Other criticisms of the effort to frame culture in Darwinian terms have been leveled by [[Biography:Richard Lewontin|Richard Lewontin]],<ref>{{cite journal | last1 = Fracchia | first1 = J. | last2 = Lewontin | first2 = R. C. | year = 1999 | title = Does culture evolve? | journal = History and Theory | volume = 38 | issue = 4| pages = 52–78 | doi=10.1111/0018-2656.00104}}</ref> [[Biography:Niles Eldredge|Niles Eldredge]],<ref>{{cite journal | last1 = Temkin | first1 = I. | last2 = Eldredge | first2 = N. | year = 2007 | title = Phylogenetics and material cultural evolution | journal = Current Anthropology | volume = 48 | issue = 1| pages = 146–153 | doi=10.1086/510463| s2cid = 53466862 }}</ref> and [[Biography:Stuart Kauffman|Stuart Kauffman]].<ref>{{cite journal | last1 = Kauffman | first1 = S | year = 1999 | title = Darwinism, neoDarwinism, and the autocatalytic model of culture: Commentary on Origin of Culture | url = http://www.cogsci.ecs.soton.ac.uk/cgi/psyc/newpsy?10.022 | journal = Psycoloquy | volume = 10 | issue = 22| pages = 1–4 }}</ref>

==See also==
* {{annotated link|Philosophy:Nature versus nurture}}
* {{annotated link|Philosophy:Adaptive bias}}
* {{annotated link|Social:Cultural selection theory}}
* {{annotated link|Philosophy:Memetics}}
* {{annotated link|Social:Sociocultural evolution}}

==References==
{{reflist|2}}

==Further reading==

===Books===
*Lumsden, C. J. and E. O. Wilson.  1981.  ''Genes, Mind, and Culture: The Coevolutionary Process.''  Cambridge, Massachusetts: Harvard University Press.
*[[Biography:Luigi Luca Cavalli-Sforza|Cavalli-Sforza, L. L.]] and M. Feldman. 1981. ''Cultural Transmission and Evolution: A Quantitative Approach.'' Princeton, New Jersey: Princeton University Press.
*Boyd, R. and P. J. Richerson.  1985. '' Culture and the Evolutionary Process''.  Chicago: University of Chicago Press.
*Durham, W. H. 1991. ''Coevolution: Genes, Culture and Human Diversity''.  Stanford, California: Stanford University Press. {{ISBN|0-8047-1537-8}}
*Tomasello, M. 1999.  ''The Cultural Origins of Human Cognition.'' Cambridge, Massachusetts: Cambridge University Press.
*Shennan, S. J. 2002. '' Genes, Memes and Human History: Darwinian Archaeology and Cultural Evolution''. London: Thames and Hudson.
*Laland, K. N. and G. R. Brown.  2002.  ''Sense & Nonsense: Evolutionary Perspectives on Human Behavior.''  Oxford: Oxford University Press.
*Boyd, R. and P. J. Richerson.  2005. ''The Origin and Evolution of Cultures''.  Oxford: Oxford University Press.
*Richerson, P. J. and R. Boyd.  2005. ''Not By Genes Alone: How Culture Transformed Human Evolution''.  Chicago: University of Chicago Press.
*Henrich, J. 2015. ''The Secret of Our Success: How Culture Is Driving Human Evolution, Domesticating Our Species, and Making Us Smarter''. Princeton: Princeton University Press.
*Laland, K.H. 2017. ''Darwin's Unfinished Symphony: How Culture Made the Human Mind''. Princeton: Princeton University Press.

===Reviews===
*Smith, E. A. 1999. [http://faculty.washington.edu/easmith/ThreeStyles.pdf Three styles in the evolutionary analysis of human behavior.] In L. Cronk, N. Chagnon, and W. Irons, (Eds.) ''Adaptation and Human Behavior: An Anthropological Perspective'' New York: Aldine de Gruyter.
*{{cite journal | last1 = Henrich | first1 = J. | last2 = McElreath | first2 = R. | year = 2003 | title = The evolution of cultural evolution | url = http://arbeit.ucdavis.edu/mcelreath/files/henrich%20mcelreath%20EA%202003.pdf | journal = Evolutionary Anthropology | volume = 12 | issue = 3 | pages = 123–135 | doi = 10.1002/evan.10110 | s2cid = 14302229 | access-date = 2008-03-27 | archive-url = https://web.archive.org/web/20080407082050/http://arbeit.ucdavis.edu/mcelreath/files/henrich%20mcelreath%20EA%202003.pdf | archive-date = 2008-04-07 | url-status = dead }}
*{{cite journal | last1 = Mesoudi | first1 = A. | last2 = Whiten | first2 = A. | last3 = Laland | first3 = K. N. | year = 2006 | title = Towards a unified science of cultural evolution | url = http://amesoudi.googlepages.com/Mesoudi_Whiten_Laland_BBS_2006.pdf | journal = Behavioral and Brain Sciences | volume = 29 | issue = 4 | pages = 329–383 | doi = 10.1017/s0140525x06009083 | pmid = 17094820 | citeseerx = 10.1.1.612.2415 | access-date = 2008-03-27 | archive-url = https://web.archive.org/web/20081216225124/http://amesoudi.googlepages.com/Mesoudi_Whiten_Laland_BBS_2006.pdf | archive-date = 2008-12-16 | url-status = dead }}
*{{cite journal | last1 = Gintis | first1 = H | year = 2006 | title = A framework for the integration of the behavioral sciences | url = http://www.umass.edu/preferen/gintis/Unity-BBS%20Print%20Version.pdf | journal = Behavioral and Brain Sciences | volume = 30 | issue = 1| pages = 1–61 | doi=10.1017/s0140525x07000581| pmid = 17475022 | s2cid = 18887154 }}
*Bentley, R.A., C. Lipo, H.D.G. Maschner and B. Marler 2007. Darwinian Archaeologies. In R.A. Bentley, H.D.G. Maschner & C. Chippendale (Eds.) ''Handbook of Archaeological Theories''. Lanham (MD): AltaMira Press.
*McElreath, R. &  Henrich, J. 2007. [https://web.archive.org/web/20070717022528/http://arbeit.ucdavis.edu/mcelreath/files/mcelreath_henrich_mce_final.pdf Modeling cultural evolution.] In R. Dunbar and L. Barrett, (Eds.), ''Oxford Handbook of Evolutionary Psychology'' Oxford: Oxford University Press.
*McElreath, R. &  Henrich, J. 2007. [https://web.archive.org/web/20070811175148/http://arbeit.ucdavis.edu/mcelreath/files/Henrich%20and%20McElreath%20final.pdf Dual inheritance theory: the evolution of human cultural capacities and cultural evolution.] In R. Dunbar and L. Barrett, (Eds.), ''Oxford Handbook of Evolutionary Psychology'' Oxford: Oxford University Press.
*{{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 }}

===Journal articles===
*{{cite journal|author=R. Boyd |author2=P. J. Richerson |editor=P. Carruthers |editor2=S. Stich |editor3=S. Laurence|title=Culture, Adaptation, and Innateness|journal=The Innate Mind: Culture and Cognition|url=http://www.sscnet.ucla.edu/anthro/faculty/boyd/Innateness%20ver%204.1.pdf|archive-url=https://web.archive.org/web/20050127195553/http://www.sscnet.ucla.edu/anthro/faculty/boyd/Innateness%20ver%204.1.pdf|url-status=dead|archive-date=January 27, 2005}}
*{{cite journal|author=P. J. Richerson |author2=R. Boyd|year=2001|title=Built for Speed, Not for Comfort: Darwinian Theory and Human Culture|journal=History and Philosophy of the Life Sciences|volume=23|issue=23|pages=425–465|pmid=12472064|url=http://www.sscnet.ucla.edu/anthro/faculty/boyd/Built%20for%20Speed,%20Not%20for%20Comfort.pdf|archive-url=https://web.archive.org/web/20060528173545/http://www.sscnet.ucla.edu/anthro/faculty/boyd/Built%20for%20Speed,%20Not%20for%20Comfort.pdf|url-status=dead|archive-date=May 28, 2006}}

==External links==

===Current DIT researchers===
* [https://web.archive.org/web/20000823024154/http://www.sscnet.ucla.edu/anthro/faculty/boyd/ Rob Boyd], Department of Anthropology, UCLA
* [http://www-evo.stanford.edu/marc.html Marcus Feldman], Department of Biological Sciences, Stanford
* [http://www.psych.ubc.ca/~henrich/home.html Joe Henrich], Departments of Psychology and Economics, University of British Columbia
* [https://archive.today/20050212095409/http://arbeit.ucdavis.edu/mcelreath/ Richard McElreath],  Anthropology Department, UC Davis
* [http://www.des.ucdavis.edu/faculty/Richerson/Richerson.htm Peter J. Richerson], Department of Environmental Science and Policy, UC Davis

===Related researchers===
* [https://people.ok.ubc.ca/lgabora/ Liane Gabora], Department of Psychology, University of British Columbia
*[http://www.psych.auckland.ac.nz/people/rd-gray/ Russell Gray] Max Planck Institute for the Science of Human History, Jena, Germany
* [http://people.umass.edu/gintis/ Herb Gintis], Emeritus Professor of Economics, University of Massachusetts & Santa Fe Institute
* [http://lalandlab.st-andrews.ac.uk/ Kevin Laland], School of Biology, University of St. Andrews
* [http://www.ucl.ac.uk/heeg/ Ruth Mace], Department of Anthropology, University College London
*[https://web.archive.org/web/20160312113541/https://sites.google.com/site/amesoudi2/ Alex Mesoudi] Human Biological and Cultural Evolution Group, University of Exeter, UK
* [https://web.archive.org/web/20080324234844/http://email.eva.mpg.de/~tomas/ Michael Tomasello], Department of Developmental and Comparative Psychology, Max Planck Institute for Evolutionary Anthropology
*[https://web.archive.org/web/20150601063550/http://www.eeb.uconn.edu/people/turchin/ Peter Turchin] Department of Ecology and Evolutionary Biology, University of Connecticut
*[http://profmarkcollard.com/ Mark Collard], Department of Archaeology, Simon Fraser University, and Department of Archaeology, University of Aberdeen

{{Evolution}}
{{Evolutionary psychology}}

{{DEFAULTSORT:Dual Inheritance Theory}}
[[Category:Anthropology]]
[[Category:Behavioural genetics]]
[[Category:Cultural anthropology]]
[[Category:Human evolution]]
[[Category:Population genetics]]
[[Category:Sociobiology]]

{{Sourceattribution|Dual inheritance theory}}