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'''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|archive-date=10 September 2017|archive-url=https://web.archive.org/web/20170910175215/http://anthro.palomar.edu/synthetic/glossary.htm#sectB|url-status=dead}}</ref> was developed in the 1960s through early 1980s to explain how [[human behavior]] is a product of two different and interacting [[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 theory|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 in judgement and decision making|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.
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===Natural selection===
Cultural differences among individuals can lead to differential survival rates 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===
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===Cultural drift===
[[Cultural drift]] is a process roughly analogous to [[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.
===Guided variation===
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