Physical Anthropology : Inbreeding

Due to the fact that anthropology's various orientations, many subjects are analyzed on their biological and social dimensions. 'There are not objects, but subjects of study', is a phrase said often in the Latin American school of physical anthropology.

One of the issues studied under the anthropological microscope, is inbreeding; the taboo subject of incest is present in the beginnings of society, and still there are some groups which do not consider incest to be taboo.

The semantic meaning of 'inbreeding', as indicated by the Greek "ενδο" (within) and γάμία (marriage, union), refers to the union between two individuals related by a common descendent, meaning that they are part of the same lineage or family. This a phenomenon that is common throughout the history of human beings, for various social, economic, religious or cultural reasons.

From biology, inbreeding is defined as the mating between individuals related by consanguinity within a genetically isolated group (Cavalli-Sforza & Bodmer, 1971).

The Blue Lagoon (1980).

Inbred unions are considered those in which the individuals have a degree of kinship greater than or equal to that of second cousins (as the genetic sequences of these unions do not differ that greatly from unions between parents without an ancestral link). The various types of endogamous unions - meaning unions between those in the same religious or social denomination - have occurred throughout the world at different time periods, since it responds to multiple factors of a cultural and religious nature.

Incestuous unions, between father-daughter, mother-son or carnal brothers are very rare, due to the common taboo-view of incest in many cultures. Although endogamous unions have occurred in periods such as Ancient Egypt, where unions between brothers of royalty were practiced, it never became a truly common practice, though it may sometimes appear that way because of the scientific investigations on these matters.

The most frequent endogamous unions are the links between cousins, both between first cousins ​​and especially between second cousins, which are often used to promote lineages or pedigrees in various parts of the world. This is the case for many specific religious groups or power elites (nobility, aristocracy).

Regarding the commonness of consanguine links between first cousins and second cousins: there are around 6.5% of people whose parents are first cousins, ​​and a low 1.56% with parents who are second cousins ​​(Álvarez, Quinteiro & Ceballos. 2011).

Family tree of King Charles II of Spain to show the practices they had.

In the course of history, inbreeding has been a resource used by the Homo Sapiens species from its origin. As the population estimate for the founding group of humans is around 10,000 individuals, the need for matings between consanguineous relatives is heavily implied.

The persistence of inbreeding as a social behaviour in human development seems to have been demonstrated from about 9,000 years ago, in the Middle East area (Kurt et al. 2013). This occurrence would continue to be present in the first historical stages as a simple consequence of the small size of the populations. However, the relationships between populations based on kinship ties will gradually form lines of power based on oligarchic lineages, that will become a keynote in the historical evolution, as is evident in the great civilisations of the Ancient World.

Inbreeding as a consequence of the scarcity of individuals, coinciding with the social belief that family consanguinity would continue a family's bloodline, would lead to a continuation in the practice of inbreeding in Europe until the Middle Ages. With the population increase reported by the Modern Age and especially from the 18th century, the causes that explain the persistence of inbreeding are religious, political-economic and social (Álvarez, Quinteiro & Ceballos. 2011).

The modern existence of inbreeding (the current areas with a high concentration of inbreed unions in the world), and the genetic outcomes of inbreeding will be explored in a later article.

Sources

Alt, K. W., Benz, M., Müller, W., Berner, M. E., Schultz, M., Schmidt-Schultz, T. H., Vach, W. (2013). Earliest Evidence for Social Endogamy in the 9,000-Year-Old-Population of Basta, Jordan. PLoS ONE, 8(6), e65649. https://doi.org/10.1371/journal.pone.0065649

Alvarez, G., Quinteiro, C., & C., F. (2011). Inbreeding and Genetic Disorder. En K. Ikehara (Ed.), Advances in the Study of Genetic Disorders. InTech. https://doi.org/10.5772/18373

Berra, T. M., Alvarez, G., & Ceballos, F. C. (2010). Was the Darwin/Wedgwood Dynasty Adversely Affected by Consanguinity? BioScience, 60(5), 376-383. https://doi.org/10.1525/bio.2010.60.5.7

Bittles, A. (2008). Consanguinity and its relevance to clinical genetics: Consanguinity and its relevance to clinical genetics. Clinical Genetics, 60(2), 89-98. https://doi.org/10.1034/j.1399-0004.2001.600201.x

Bittles, A. H., & Black, M. L. (2010). Consanguinity, human evolution, and complex diseases. Proceedings of the National Academy of Sciences, 107(suppl_1), 1779-1786. https://doi.org/10.1073/pnas.0906079106

Charlesworth, D. (1987). Inbreeding Depression and its Evolutionary Consequences, 32. https://doi.org/10.1146/annurev.es.18.110187.001321

Charlesworth, Deborah, & Willis, J. H. (2009). The genetics of inbreeding depression. Nature Reviews Genetics, 10(11), 783-796. https://doi.org/10.1038/nrg2664

Hedrick, P. W. (1994). Purging inbreeding depression and the probability of extinction: full-sib mating. Heredity, 73(4), 363-372. https://doi.org/10.1038/hdy.1994.183

Hussain, R., & Bittles, A. H. (1998). THE PREVALENCE AND DEMOGRAPHIC CHARACTERISTICS OF CONSANGUINEOUS MARRIAGES IN PAKISTAN. Journal of Biosocial Science, 30(2), 261-275. https://doi.org/10.1017/S0021932098002612

Hussain, R., & Bittles, A. H. (2000). SOCIODEMOGRAPHIC CORRELATES OF CONSANGUINEOUS MARRIAGE IN THE MUSLIM POPULATION OF INDIA. Journal of Biosocial Science, 32(4), 433-442. https://doi.org/10.1017/S0021932000004338

Lynch, M. (1991). THE GENETIC INTERPRETATION OF INBREEDING DEPRESSION AND OUTBREEDING DEPRESSION. Evolution, 45(3), 622-629. https://doi.org/10.1111/j.1558-5646.1991.tb04333.x

Michod, R. E. (1980). EVOLUTION OF INTERACTIONS IN FAMILY-STRUCTURED POPULATIONS: MIXED MATING MODELS, 22.

Image Sources

Charles II of Spain Family tree

Alasdair Wilkins. (n.d.). Why inbreeding really isn’t as bad as you think it is. Retrieved 17 January 2022, from https://gizmodo.com/why-inbreeding-really-isnt-as-bad-as-you-think-it-is-5863666

Movie shots TARA BLOCK. (n.d.). Womb | Movies About Incest | POPSUGAR Love & Sex Photo 16. Retrieved 17 January 2022, from https://www.popsugar.com/love/photo-gallery/40321605/image/40322469/Womb