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Chickens (gallus gallus domesticus) is the most populous domesticated animal on Earth has highly disputed origins and timeframe of their domestication. Evidence of the range of the ancient chicken extends back 6 million years ago in the Messinian period of the Pleistocene with the fossil remains of Gallus europeaus in the UK and gallus Aesculapi in Greece. From that time the range extended in a diagonal band starting in England, through France, Italy, Greece, Turkey, India and its subcontinent, and south west China including Tibet, and into South-East Asia, Indonesia and Oceania. In all areas west of India, the chicken went extinct prior to domestication (Meig, 2019). Within the past 4,000 years there are only four species of living chicken remaining in which the modern-day domesticated chicken could hail from. Despite the most recent archaeological, DNA analysis, and even historical texts and relief studies; the time and point of domestication is still highly contested (Peters, et.al., 2022). Darwin even had been torn by the idea that the Red Jungle Fowl (RJF) which is from South-East Asia, was domesticated afar in India (Lawlar, 2020).

Research used varied publications from 2011 - 2022 with multiple points of origin domestication evidence support (China, Africa, South-East Asia, or Indian), linguistics in Africa, and multiple methodologies (archeological, mtDNA haplotyping, and genome reconstruction) which are explained below in chronological order of publication.

The first review publication “Chicken domestication: from Archeology to Genomics '' is from 2011 where a brief history of chicken, and theories of domestication by reviewing previous archaeological remains surmised, linguistics, trade routes, and genome sequences are reviewed. Linguistics analysis for mention of the chicken on the continent of Africa only found a Eastern route or Northern route with no originating language for chicken from the West or South. This article investigates then research on the maternal line, mtDNA, to construct a domestication pathway. This research created 169 haplotypes with 9 clades, A to I. The result of this research was that there was no single material origin, or matrilineal clade, found and a theory of multiple origins and hybridization of domestication in South and South-East Asia was concluded (Tixer-Boichard, et.al., 2011). The authors deduced using a published whole genome in 2004 of an inbred RJF which gave the basis of a high polymorphism. Other ways the origins of domesticated chicken was explained was through the phenotype skin color of the BCDO2 gene. White leg color is seen in Green and RJF. The yellow skin mutation is seen in Gray and Ceylon Junglefowl. The gray and yellow skin color is thought to have a common ancestor. The yellow skin color was traced using the gene BCDO2 back to G. sonneratii species of western India. India is one of two locations proposed for domestication in previous research and  domestication is noted as beginning most likely for entertainment and cockfighting. This is backed up with bones found in the gaming and cockfighting are larger than wild type Red Jungle Fowl. Also the authors noted the remains of chickens in China going back ~6000 BC.

In the 2018 publication of ‘Was chicken domesticated in northern China? New evidence from mitochondrial genomes.” The authors looked into the highly contested domestication theories, especially the one in which our previous article of findings of bones of chickens dating to ~6000 BC were identified. Coupled with the earliest record of cockerel game fighting being recorded in 517BC. Even though this is the earliest date at the time, the theory of origination of the chicken in China was squelched when further sequence data and archaeological studies found the C1 haplogroup of China was not found in any Red JUngle Fowl (RJF) in south-east Asia. This shows that the chickens in China came from south-east Asia and not the reverse.

In “The wild species genome ancestry of domestic chickens” 87 genomes were analyzed which the authors reviewed and reported out the times of diversification of each subspecies. It is here the polyphyletic tree is outlined with the pheasant is a common ancestor prior to the junglefowl. Diversification is noted in a large gap between 20,736,660 years of pheasant to 3,997,328 to the RJF diversification. The gray and green junglefowl are noted to be sister species diversifying under the RJF backed up by the genetic lineage phenotype of non-yellow legs. To note, understand that yellow coloring of the legs of chickens is a recessive trait, with White (W) being dominant. The White is from the Red Jungle fowl lineage. The domestic chicken lineage then, with speciation in the last couple centuries cannot rule out hybridization or admixture of all the four species of junglefowl for creation of the current domesticated chicken and with support to a south-east Asia majority source.

A second article from 2020 is tilted “863 genomes reveal the origin and domestication of chicken” immediately flushes out previous and any archeological research and recording of chickens bones due to the lack of radiocarbon dating and because there are no physical osteomorpologiccal, or bone, markers which allow us to distinguish early domestic, RJF, and subspecies from one another. Authors continue to note that relying solely on RJF as the genetic origin does not take into the consideration the current wild species of RJF are not reliable sources of ancient DNA for wildtype chickens. This is due to the hybridization from back breeding of  emerging domesticated chickens back into the wildtype RJF. To determine which of the 4 subspecies the domestic chicken derived. The most interesting thing from this study is that there are unclassified lineages found. Earliest domestic lineages were found in China, Thailand, Vietnam and Indonesia.This research also found the chicken began diversification at about 9000 years ago, at the transition of the Holocene and major climate shifts. The authors also found through the genetic analysis that traits for reproduction, behavior and growth were positively selected for in the domestication process.

A third article of 2020 we find the authors take a moment to explain how chickens evolved from the pheasant and reiterate the most current summeration of the genetic studies to date. Pheasants are the common ancestor of chickens, but when the domestic chicken betganThe authors took the process of sequencing 863 indigenous village chicks and wild jungle fowl from villages across Asia and Africa. Their results point to the domestication of chickens in a triangle shaped area that has Bangladesh as the upper left, Laos as the upper right and Malaysia as the bottom point. This includes Thailand, southern China and Myanmar. There is evidence from the authors studies that a South Asian (mainly west of Bangladesh including India) did have an influence on the chicken but only after initial domestication in Southeast Asia. Researchers also suggest that the lineage of the domesticated chicken somehow was tied into millet and rice farming in the area of southeast Asia 4500 years ago. The research leaves many questions still despite the intense genetic analysis. There is strong consensus that combining archaeological data and genetics is important to tease out the history of domestication.

The fourth article named “The biocultural origins and dispersal of domestic chickens” the authors investigate prior research and the archaeological contexts of chicken remains and early domestication and distribution of RJF. The authors intricately cover the prior theories and evidence of domestication over southwest, southeast and northeast Asia, northeast Africa and Europe. Authors conclude that the first archaeological records point to a incorporation into human societies ~1650 to 1250 BCE in central Thailand. From here chickens were brought and dispersed in all other areas fairly swiftly.

With rice and millet farming beginning 3000 BCE in the Yangtze valley moving southward into south east Asia thereafter. This required major landscape altercations from forested to fields. This grain and cereal cultivation over the decades and centuries had a amount of unused and lost produce in which the authors speculate that these newly domesticated chickens would have been able to be nourished by and thus allowed specific gene promotion as they learned to keep closer promitities and thus dependence, domestication, to the humans in each generation.

It is noted that in places where wet rice farming in which chickens could have been present, there lacked any evidence of their Neolithic presence ~ 3500 BCE. Which is expected as ancient  chickens do not do well in wet environments and the authors presumed that they would proliferate in dry fields better. This is a pattern in what is seen with other domesticated animals as well. This linking of the dry rice and millet farming beginnings, and of research and evidence of chicken domestication in the same areas make for a solid theory for location.

Conclusion

The research in the 10 years leading up to today has been heavily influenced by genetics and genome sequencing. As seen with Darwin himself, using phenotypic features and archaeological evidence only gets you so far. On the other hand, using purely genetic information is limited as well due to the crossbreeding, back breeding and now understanding there is no pure living junglefowl which did not cross with early domesticated chicken subspecies.

It is seen with the most recent analysis that researchers are solving the question of chicken domestication with interdisciplinary resources. Pulling from linguistics, to archaeological remains, to culture and burial evidence, down to the genome itself; the authors are able to decipher and piece together the chicken as a domestic animal and when and where and most importantly how.