From the origin of roosters, hens and chickens

Charles Darwin thought that today's roosters come from the red wild rooster, Gallus gallus a tropical species from the jungles of Southeast Asia. They are very similar and hybrid, in fact. The species has five wild subspecies that are distributed in a wide geographical area ranging from the jungles of Indonesia to the foothills of the Himalayas, in Pakistan. In fact, the English naturalist believed that the rooster was domesticated in India.

Darwin was right about the first, but wrong about the second. Gallus gallus is indeed the species from which our chickens come, but it seems that they were not domesticated on the Indian subcontinent. From skeletal remains found in different places in Asia, many archaeologists thought that chickens were domesticated about 9000 years ago in northern China, first, and about 4000 years ago in Pakistan -in the Indus Valley-, for second time.

The results of an investigation have recently been published in which they have analyzed the genome of 863 individuals belonging to different varieties of domestic roosters, the four wild species and the five subspecies of the wild red rooster. The research team has concluded that the current domestic roosters are derived from a subspecies of the latter, Gallus gallus spadiceus which is currently distributed in southwestern China, northern Thailand and Burma. But after domestication, they were moved to Southeast and South Asia. In the areas where they were taken there were (and still are) populations of other species of wild rooster and of other varieties (or subspecies) of the red rooster, and with many of them they interbred and left fertile offspring. Therefore, the current chickens have a very convoluted genetic past, because lineages of other species and subspecies have been added to the original. All domestic roosters in China, Southeast Asia and South Asia possess hybrid genomes, in which up to almost a quarter come from subspecies of Gallus gallus other than the native one.

They have also found that domestic roosters diverged from the wild red rooster about 9500 years ago, and therefore before domestication began, so this would not have been the trigger for the divergence between the two lineages, the wild and the domestic. The timing of this lineage separation coincided with a time of intense climate change, following the transition from the Pleistocene to the Holocene, when temperatures rose and there was an increase in monsoon activity in Southeast Asia. It is possible that the changing environmental conditions favored the diversification of the original lineage ( Gallus gallus spadiceus ) and that some or some of its variants were later domesticated.

As is often the case with species used for human consumption , genes related to production have undergone strong positive selection, which, logically, is the result of the search for rapid growth and high egg production. After all, chickens have become the most abundant farm animals on the planet; there are about three for every human being.

The wild rooster variety is currently in danger of extinction, because it may end up diluting its genetic background in the many more numerous domestic roosters with which they hybridize, thus losing a valuable source of genetic diversity. It would be fulfilled, in a perhaps unusual way, that Spanish paremia that says that there is no worse splinter than that of the same wood.

Source: Ming-Shan Wang (2020): 863 genomes reveal the origin and domestication of chicken. Cell Research 0: 1–9

About the author: Juan Ignacio Pérez ( @Uhandrea ) is Professor of Physiology and coordinator of the Chair of Scientific Culture of the UPV / EHU

The article On the origin of roosters, hens and chickens has been written in Notebook of Scientific Culture .

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