The Origin of the Chicken

i-66885db037f0fdfa03ea6dcc53abc6b2-red_junglefowl.jpgFrom whence the humble chicken? Gallus gallus is a domesticated chicken-like bird (thus, the name “chicken”) that originates in southeast Asia. Ever since Darwin we’ve known that the chicken originated in southeast Asia, although the exact details of which one or more of several possible jungle fowls is the primal form has been debated. The idea that more than one wild species contributed to the early chicken has been on the table for a long time, though perhaps not as long as the chickens themselves have been on the table.i-372e5355e65109318f9e9b938b877e84-chicken.jpgNotice the yellow legs on this chicken. If you pluck out the feathers, you’ll notice that the skin is yellow as well. But if you go find, say, a crow, and pluck its feathers, it will be grayish in color. Or maybe black, I don’t know, it’s been a while since I’ve defeathered a crow. The point is, that some birds are yellow, some are not.ResearchBlogging.orgThere is a gene that is expressed in certain tissues that produces an enzyme that cleaves the carotenoid molecules that provide the yellow color. If there is no functional copy of this gene (if the individual is homozygotic for the broken version) then this cleaving does not happen, and you get a yellow bird (depending on other factors we shall ignore).In short, new research confirms as previously thought that the red jungle fowl (Gallus gallus) is ancestral to the modern chicken, as Darwin suspected. But this research also suggests that another bird, the grey jungle fowl (Gallus sonneratii) also contributed to the chicken’s genome, providing the yellow color we see on this chicken’s legs.The research, reported in PLoS Genetics, gives us two results. One is the first characterization of the process of pigmentation mentioned above, and the second is a new family tree for this bird.

Many bird species possess yellow skin and legs whereas other species have white or black skin color. Yellow or white skin is due to the presence or absence of carotenoids. The genetic basis underlying this diversity is unknown. Domestic chickens with yellow skin are homozygous for a recessive allele, and white skinned chickens carry the dominant allele. As a result, chickens represent an ideal model for analyzing genetic mechanism responsible for skin color variation. In this study we demonstrate that yellow skin is caused by regulatory mutation(s) that inhibit expression of the beta-carotene dioxygenase 2 (BCDO2) enzyme in skin, but not in other tissues. Because BCDO2 cleaves colorful carotenoids into colorless apocarotenoids, a reduction in expression of this gene produces yellow skin. This study also provides the first conclusive evidence of a hybrid origin of the domestic chicken. It has been generally assumed that the red junglefowl is the sole ancestor of the domestic chicken. A phylogenetic analysis, however, demonstrates that though the white skin allele originates from the red junglefowl, the yellow skin allele originates from a different species, most likely the grey junglefowl. This result significantly advances our understanding of chicken domestication.

Here is the phylogenetic tree that the authors of this paper present:i-a782d8d10ab087febef2b5b4a719fe02-chicken_tree.jpgClick here for a much larger image (84kb)You will read in press reports that “Darwin got it wrong” when it comes to chickens. Let’s have a look at what he said and see how wrong he was. Darwin addressed the two major theories of his time. One is a multiregional theory, much like the now discredited version of human evolution, where each kind of chicken was domesticated from a different wild form. The other is that all descended from one ancestor, Gallus gallus bankiva, also known as Gallus bankiva.Darwin uses chickens in a big way in developing his ideas about evolution. Chickens were perhaps as important as pigeons for examining breed characteristics. Therefore, he wrote quite a bit about chickens. In the end, he favored the single origin hypothesis, but he also describes the primordial species of his choosing … the red jungle fowl … as much more diverse in character than it is generally characterized today…

… Gallus bankiva, has a much wider geographical range than the three previous species; … This species varies considerably in the wild state. Mr. Blyth informs me that the specimens, both male and female, brought from near the Himalaya, are rather paler coloured than those from other parts of India; whilst those from the Malay peninsula and Java are brighter coloured than the Indian birds. I have seen specimens from these countries, and the difference of tint in the hackles was conspicuous. The Malayan hens were a shade redder on the breast and neck than the Indian hens. The Malayan males generally had a red ear-lappet, instead of a white one as in India; but Mr. Blyth has seen one Indian specimen without the white ear-lappet. The legs are leaden blue in the Indian, whereas they show some tendency to be yellowish in the Malayan and Javan specimens. In the former Mr. Blyth finds the tarsus remarkably variable in length. According to Temminck20 the Timor specimens differ as a local race from that of Java. These several wild varieties have not as yet been ranked as distinct species; if they should, as is not unlikely, be hereafter thus ranked, the circumstance would be quite immaterial as far as the parentage and differences of our domestic breeds are concerned. The wild G. bankiva agrees most closely with the blackbreasted red Game-breed, in colouring and in all other respects, except in being smaller, and in the tail being carried more horizontally. But the manner in which the tail is carried is highly variable in many of our breeds,…(Darwin 1868:233)

What we see here (my emphasis added) is evidence that skin color varied across different populations of this species.The study at hand asserts:

On the basis of observed character differences and cross-breeding experiments, Darwin concluded that domestic chickens were derived solely from the red junglefowl, though this was later challenged by Hutt [1], who stated that as many as four different species of junglefowls may have contributed to chicken domestication. Molecular studies of mtDNA and retroviral insertions have supported Darwin’s view. A study that analyzed both repeat nuclear elements and mitochondrial sequences found evidence that grey and Ceylon junglefowls may hybridize with domestic chickens, but did not provide evidence that these two species have contributed to chicken domestication. To date, no studies have compared gene sequences associated with a specific phenotype found in domestic chickens across numerous wild junglefowls and domestic breeds….We searched for the causal mutation … This analysis revealed a surprisingly high sequence diversity between the two groups (0.81%), well above the genome average for chicken (~0.5%) [15] and approaching the sequence divergence between chimpanzee and human (1.2%). We therefore included three other species of junglefowls in the sequence comparison: grey (G. sonneratii), Ceylon (G. lafayetii), and green (G. varius) junglefowls. This step was also motivated by the fact that grey and Ceylon junglefowls have red or yellowish legs which implies deposition of carotenoids and a Y/Y genotype…In contrast, mtDNA sequences from the same samples showed the expected pattern in which domestic chickens cluster with red junglefowl within a clade well separated from other junglefowls

The grey and red jungle fowl have, at present, disjunct ranges, but that may be a product of recent ecological changes, including human alterations of habitats. Also, in the early days of chicken domestication, there is no reason to suspect that a single origin would be followed by immediate isolation from wild forms, and in fact, all the available evidence including that reported here suggests the contrary.I think the truth of the matter is that Darwin did not really get the origin of the chicken wrong … he had it substantially right. Rather, Darwin had a better idea of variation in the wild forms than we may appreciate today, and he leaned a bit more towards a simpler history at the start than we tend to today. That’s not bad considering that all of the modern theory about origins of domesticated forms post dates, and often derives from, Darwin.In other words, Newton understood gravity, so today we can design an airplane. But if Newton designed and airplane that did not fly, would that mean that he got gravity wrong?I think not.


(More on Darwin here)Darwin, C. R. 1868. The variation of animals and plants under domestication. London: John Murray. First edition, first issue. Volume 1.Eriksson, J., Larson, G., Gunnarsson, U., Bed’hom, B., Tixier-Boichard, M., StrÃ?¶mstedt, L., Wright, D., Jungerius, A., Vereijken, A., Randi, E., Jensen, P., Andersson, L., Georges, M. (2008). Identification of the Yellow Skin Gene Reveals a Hybrid Origin of the Domestic Chicken. PLoS Genetics, 4(2), e1000010. DOI: 10.1371/journal.pgen.1000010

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17 Responses to The Origin of the Chicken

  1. Larry Ayers says:

    Nice summary, Greg! Have you ever seen a jungle fowl? They are quite the impressive birds!

  2. Greg Laden says:

    Certainly not in the wild! I don’t recall having seen one in a zoo either.

  3. postdiluvian says:

    Isn’t “from whence” redundant?

  4. Larry Ayers says:

    Rural chicken fanciers sometimes keep jungle fowl. Some years ago when I was living in rural Knox County I was helping a young boy with a 4H woodworking project. The boy’s mother was a commercial dog-breeder and also raised chickens. She had one jungle cock but had to keep it fenced away from other fowl. She told me “That rooster will kill any other chicken it sees!”It was an impressive bird, standing about three feet tall, and it looked to be ready to take on all intruders. It probably wasn’t a pure specimen of the ancient oriental chickens, but it was a lot closer than your avarage Rhode Island Red!

  5. Greg Laden says:

    postdiluvian: It works in English. If we followed pure grammatical logic in English, no one would ever be able to return to his or her respective seat, whence the lobby, following intermission. So, technically, it is redundant, but language is language and the greatest of authors have had their characters, chickens, etc. come from a whence. Your objection would be totally valid in the 13th century, though.Larry: Wow. I would have figured a jugnle fowl was much smaller than that. Are you sure it wasn’t a goose suffering an identity crisis? Of course, eastern Tennessee has all kinds of stuff like that, I guess.

  6. I googled “from whence” and it turns out you’re right. Apparently it’s been used by Dickens, Twain, and the King James Bible. I feel so out of touch.

  7. Alan Kellogg says:

    The San Diego Zoo has red-legged jungle fowl running loose on the grounds. The story goes that the first specimens were imported for the Panama Exposition of 1914 and allowed to run loose on exhibition grounds in Balboa Park. When the San Diego Zoological Society was established in 1916 the surviving birds and their descendants were relocated to zoo grounds, though canine depredations weren’t ended until fencing was finally in place, and the stray dog problem in the area brought under control.

  8. Whodunnit says:

    One of the parks in Malmö, Sweden also has wild (or semi-wild) fowl running about. These are quite small though, only about a foot high.It also have peacocks.

  9. Greg Laden says:

    postdilulvian: I feel your pain, man. Ever since the printing press it has been impossible to keep up.Alan: Interesting. I’ve been to the SD zoo. This is probably why I have this nagging feeling I’ve seen j. fowl before.

  10. stewart says:

    There are also jungle fowl in Hawaii, brought by the Polynesians, I think. Go along the North Shore of Oahu.

  11. Greg Laden says:

    Go along the North Shore of Oahu.That would be nice. It is probably warmer than the 12 degrees F we have right now….

  12. Thanks for the update. I have a webpage on chicken origins at http://www.coconutstudio.com/Chickens.htm.In my Philippines small town, chicken fights are a regular Sunday event, and the local chickens are selected for their fighting ability rather than their meat.You’d be hard-pressed to differentiate a jungle fowl and a fighting cock, or a feral chicken. My helper’s family used to go to the Agusan Marsh in North Mindanao to snare wild jungle fowl that they would crossbreed with their own stock.

  13. BENCAULK says:

    help american

  14. uswa says:

    im commenting this cause i look like a chicken ma real name is uswa

  15. u no says:

    danm chickins i hate them i love chicks

  16. Gaby says:

    I love chickens too and this is a great post.. :)Backyard Chicken

  17. Joanna Grammon says:

    I grew up in the lower Yakima Valley, and was given a small flock of banty chickens. They looked like the depictions of Dutch banty stock, which in turn were imported red jungle fowl from Indonesia. My flock were ‘free-range’ and thus were introduced to a fighting cock rooster, a runaway from the nearby Filipino farmer. This ‘jungle fowl’ joined my banty flock and before long, our Irish Setter decided they were no longer domesticated banty chickens, which he had left unmolested, but wild and ergo fair game. He began killing my chickens. I even tied a dead chicken around his neck, a supposed cure, but it didn’t work. After that, he was tied on a long leash to the backyard tree. I don’t know what happened to the flock when we moved and left them with the new owners. They certainly were beautiful. long-tailed jungle fowl.

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