The history of chickens (Gallus domesticus) is still a bit of a puzzle. Scholars agree that they were first domesticated from a wild form called red junglefowl (Gallus gallus), a bird that still runs wild in most of southeast Asia, most likely hybridized with the gray junglefowl (G. sonneratii). That occurred probably about 8,000 years ago. Recent research suggests, however, there may have been multiple other domestication events in distinct areas of South and Southeast Asia, southern China, Thailand, Burma, and India.

Since the wild progenitor of chickens is still living, several studies have been able to examine the behaviors of wild and domestic animals. Domesticated chickens are less active, have fewer social interactions with other chickens, are less aggressive to would-be predators, are less susceptible to stress, and are less likely to go looking for foreign food sources than their wild counterparts. Domestic chickens have increased adult body weight and simplified plumage; domestic chicken egg production starts earlier, is more frequent, and produces larger eggs.

Chicken Dispersals

Chickens, Chang Mai, Thailand. David Wilmot

The earliest possible domestic chicken remains are from the Cishan site (~5400 BCE) in northern China, but whether they are domesticated is controversial. Firm evidence of domesticated chickens isn't found in China until 3600 BCE. Domesticated chickens appear at Mohenjo-Daro in the Indus Valley by about 2000 BCE and from there the chicken spread into Europe and Africa. Chickens arrived in the Middle East starting with Iran at 3900 BCE, followed by Turkey and Syria (2400–2000 BCE) and into Jordan by 1200 BCE.

The earliest firm evidence for chickens in east Africa are illustrations from several sites in New Kingdom Egypt (1550–1069). Chickens were introduced into western Africa multiple times, arriving at Iron Age sites such as Jenne-Jeno in Mali, Kirikongo in Burkina Faso and Daboya in Ghana by the mid-first millennium CE. Chickens arrived in the southern Levant about 2500 BCE and in Iberia about 2000 BCE.

Chickens were brought to the Polynesian islands from Southeast Asia by Pacific Ocean sailors during the Lapita expansion, about 3,300 years ago. While it was long assumed that chickens had been brought to the Americas by the Spanish conquistadors, presumably pre-Columbian chickens have been identified at several sites throughout the Americas, most notably at the site of El Arenal-1 in Chile, ca 1350 CE.

Chicken Origins: China?

Two long-standing debates in chicken history still remain at least partially unresolved. The first is the possible early presence of domesticated chickens in China, prior to dates from southeast Asia; the second is whether or not there are pre-Columbian chickens in the Americas.

Genetic studies in the early 21st century first hinted at multiple origins of domestication. The earliest archaeological evidence to date is from China about 5400 BCE, in geographically widespread sites such as Cishan (Hebei province, ca 5300 BCE), Beixin (Shandong province, ca 5000 BCE), and Xian (Shaanxi province, ca 4300 BCE). In 2014, a few studies were published supporting the identification of early chicken domestication in northern and central China (Xiang et al.). However, their results remain controversial.

A 2016 study by Chinese bioanthropologist Masaki Eda and colleagues of 280 bird bones reported as chicken from Neolithic and Bronze age sites in northern and central China found that only a handful could securely be identified as chicken. German archaeologist Joris Peters and colleagues (2016) looked at environmental proxies in addition to other research and concluded that the habitats conducive to jungle fowl were simply not present early enough in China to allow for the domestication practice to have taken place. These researchers suggest that chickens were a rare occurrence in northern and Central China, and thus probably an import from southern China or Southeast Asia where evidence of domestication is stronger.

Based on those findings, and despite the fact that southeast Asian progenitor sites have not as yet been identified, a northern Chinese domestication event separate from that of southern China and Southeast Asia does not at present seem likely.

Pre-Columbian Chickens in America

In 2007, American archaeologist Alice Storey and colleagues identified chicken bones at the site of El-Arenal 1 on Chile's coast, in a context dated well before the 16th-century medieval Spanish colonization, ca. 1321–1407 cal CE. The discovery is considered evidence of pre-Columbian contact of South America by Polynesian sailors, but that is still a somewhat controversial notion in American archaeology.

However, DNA studies have provided genetic support, in that chicken bones from el-Arenal contain a haplogroup which has been identified at Easter Island, which was founded by Polynesians around 1200 CE. The founding mitochondrial DNA cluster identified as Polynesian chickens includes A, B, E, and D. Tracing sub-haplogroups, Portuguese geneticist Agusto Luzuriaga-Neira and colleagues identified sub-haplotype E1a(b) which is found in both Easter Island and el-Arenal chickens, a key piece of genetic evidence supporting the pre-Columbian presence of Polynesian chickens on the coast of South America.

Additional evidence suggesting pre-Columbian contact between South Americans and Polynesians has also been identified, in the form of ancient and modern DNA of human skeletons in both locations. Currently, it seems likely that the chickens at el-Arenal were likely brought there by Polynesian sailors.