Domestic chickens and black rats from Asia were introduced to the east coast of Africa via maritime routes between the 7th and 8th centuries, a study has found.
Researchers analyzed the ancient DNA and proteins from bone samples in eastern Africa, confirming that the earliest samples of chickens and rats were found at open-air island port sites.
The study suggests that animals were introduced by traders engaged in the robust Indian Ocean maritime trade, and subsequently spread inland.
Domestic chickens and black rats from Asia were introduced to the east coast of Africa via maritime routes between the 7th and 8th centuries. This map shows the findings of that study (black box) and the context of arrivals and spread of Asian fauna in other parts of Africa
The study, published in the journal PLOS ONE, analyzed DNA and proteins from 496 bone samples from 22 island, coastal and inland sites in eastern Africa to learn more about how Asian fauna was introduced into Africa.
The Swahili coast has long been an important point of contact between Asia and Africa.
This cultural region, stretching from southern Somalia to northern Mozambique, includes many islands as well as the Comoros and Madagascar.
During the Medieval period, from the 7th to the 15th century AD, maritime trade between this regions and other areas of the Indian Ocean.
The archaeological evidence from this large trade network includes imported ceramics, glass beads, and Asian crops.
Now, domestic chickens and black rats can be added to this list.
The study shows that there were multiple introductions of domestic chickens – today an important food source and and ritually important species – to different parts of Africa at different times.
However, the introduction of rats was not as useful – the rats that were carried on ships to East Africa were likely major pests, and the simultaneous arrival on the coast of domestic cats, a pest-control species, was most likely not an accident.
‘Archaeologists have been debating the timing, mechanisms and social contexts of the arrival of Asian plants and animals to eastern Africa for a long time,’ says Dr Nicole Boivin, a researcher at the Max Planck Institute for the Science of Human History, Jena, Germany and the senior author of the study.
There are some competing models – on the one hand, there’s a model of a very early arrival of Asian species starting around 3000 BC, as suggested by some previous studies.
On the other hand, another model suggests a more modest, mid-first millennium AD arrival in connection with the archaeologically-confirmed maritime trade routes.
HOW THEY DID THE STUDY
The study, published in the journal PLOS ONE, analyzed DNA and proteins from 496 bone samples from 22 island, coastal and inland sites in eastern Africa to learn more about how Asian fauna was introduced into Africa.
The researchers analyzed bone samples from 52 possible chicken samples and 444 possible rat samples.
‘One challenge for any biomolecular analysis of tropical specimens is the poor preservation of organic materials in hot and humid conditions,’ says Dr Mary Prendergast, a researcher at Saint Louis University’s Madrid Campus and the lead author of the study.
Wet-sieving at the site of Ras Mkumbuu, Pemba Island, Zanzibar, Tanzania. Ras Mkumbuu is a 10th century Swahili trading port. Remains of animals, including those analyzed in the study, were recovered at this site
To address this problem, the researchers applied a variety of standard and new techniques to analyze both the bones and their ancient DNA and proteins, and they also radiocarbon dated the samples.
For the black rats, the researchers used Zooarchaeology by Mass Spectrometry (ZooMS), a method used to analyze ancient proteins and identify species by their ‘collagen fingerprints.’
Because proteins preserve better than DNA in tropical settings, ZooMS offers the possibility of quickly identifying species in a wide range of preservation states.
To tackle this debate, the researchers analyzed bone samples from 52 possible chicken samples and 444 possible rat samples.
‘One challenge for any biomolecular analysis of tropical specimens is the poor preservation of organic materials in hot and humid conditions,’ says Dr Mary Prendergast, a researcher at Saint Louis University’s Madrid Campus and the lead author of the study.
To address this problem, the researchers applied a variety of standard and new techniques to analyze both the bones and their ancient DNA and proteins, and they also radiocarbon dated the samples.
For the black rats, the researchers used Zooarchaeology by Mass Spectrometry (ZooMS), a method used to analyze ancient proteins and identify species by their ‘collagen fingerprints.’
Excavations in Kuumbi Cave, Zanzibar, Tanzania. Avian remains recovered at this site that were originally identified morphologically as chickens were shown to actually be native guinea fowl when analyzed with ZooMS, a method for identifying species by their ‘collagen fingerprints’
Because proteins preserve better than DNA in tropical settings, ZooMS offers the possibility of quickly identifying species in a wide range of preservation states.
The team confirmed that chickens were present at open-air port sites in the Tanzanian island of Zanzibar as early as the 7th to 8th century AD.
People who were living at these sites at the time were known to have engaged in maritime trade in the Indian Ocean, and the findings suggest that chickens were introduced via these trade networks.
Black rats also appear in the islands around the 7th to 8th century AD at port and cave sites, with a potential earliest date of the 5th century AD at the port site of Unguja Ukuu in Zanzibar.
People who were living at tje open-air ports of Tanzania at the time were known to have engaged in maritime trade in the Indian Ocean, and the findings suggest that chickens were introduced via these trade networks
The rats most likely arrived as stowaways on trade vessels, as they did in many places around the world.
Chickens and rats, however, do not appear on the mainland until much later, in the second millennium AD.
The findings present additional evidence of the contact and interactions between the peoples of the Indian Ocean.
As is the case today, ancient trade and shipping helped bring new animals, plants and foods, but also spread invasive species.
There was an increase in these transfers of animals and plants in the Medieval period, when maritime trade in the Indian Ocean seems to have intensified.
Researchers confirmed that chickens were present at open-air port sites in the Tanzanian island of Zanzibar as early as the 7th to 8th century AD. Pictured is Stone Town, Zanzibar’s Port
The arrival of rats, a known vector for the plague, comes around the same time as the Justinian Plague outbreak of 541-542 BC in the Eastern Roman Empire and around the Mediterranean.
Plague is currently a disease of serious concern in Madagascar and eastern Africa, where it kills more people than anywhere else in the world.
Rats are also transform ecosystems, and on many islands globally they may have contributed to species extinctions after they were introduced.
Researchers at the Max Planck Institute for the Science of Human History are currently working on trying to understand the impacts of rats on eastern African islands, as well as their global spread and role in pathogen dispersal.
The arrival of rats, a known vector for the plague, comes around the same time as the Justinian Plague outbreak of 541-542 BC in the Eastern Roman Empire and around the Mediterranean