The world teems with hybrid life. Our genomes, once thought to be singular branches on the tree of life, have been revealed by modern sequencing technology to be patchworks, featuring portions of genetic code borrowed from everything from our Neanderthal and Denisovian cousins to our distant prokaryotic relatives. Agricultural fields and groves are filled with hybrid plant species, from ancient hybrids like peanuts and oats to novel creations like triticale, a hybrid of rye and wheat bred in nineteenth century Europe, or the blood lime, a citrus hybrid designed by the Australia government in the early 02000s in order to investigate salt resistance in crops.
While crop hybridization has been an accepted part of the plant world since the dawn of agriculture, the hybrid nature of our DNA remained hidden until very recently. The history of animal hybrids lies somewhere between those poles of secret and accepted; at various times in human history these hybrid species have been status symbols, vital beasts of burden, or cautionary tales.
A recent study in Science Advances provides insight into one of the earliest intentionally created hybrid animal species: kungas. A hybrid of the common donkey and the Syrian wild ass (or hemippe), the kunga served as a status symbol in Ancient Mesopotamia, its strength and speed allowing it to act as a valuable steed to Bronze Age rulers prior to the introduction of domesticated horses to the region around 02000 BCE. Kungas were often buried with the rulers that they served, with one site in what is now Northern Syria containing separate chambers to house the remains of kungas. Their trade was a key factor in the economic and diplomatic relations between states in ancient West Asia, including the Levantine Eblaites and the Mesopotamian Sumerians.
For centuries, archeologists debated the precise lineage that produced the kunga, with some scholars claiming that they descended almost entirely from Persian onagers and others proposing alternate hybrid makeups. The remaining cuneiform sources we have on breeding kungas are frustratingly vague on details, merely noting that the equids largely originated from the Eblaite city of Nagar and that they descended from donkeys and the anše-edin-na, or “equid of the desert,” a mysterious name that could refer to a wide range of wild equid species.
The newly published research on kungas uses contemporary genetics techniques to parse out the precise provenance of the breed. Researchers from the University of Paris sequenced and performed quantitative PCR analysis on a mix of hair samples from more recent equids and bone samples from their Bronze Age relatives, analyzing both mitochondrial DNA, which is inherited maternally, and Y-chromosome DNA, which is inherited paternally.
Their analysis showed conclusively that the kungas were first generation hybrids, born exclusively from female donkeys and male Syrian wild asses. A full genome principal component analysis additionally showed that their genetic makeup “shares equal ancestry from donkey and hemippe” — a true, evenly mixed hybrid. Much like their fellow equine hybrid the mule, the kunga was likely sterile.
The kunga fell out of favor after a few centuries of Mesopotamian cultural prominence, displaced by the arrival of horses from the steppe to the region. With the extinction of their male halves, the hemippe, in the 01900s, the kunga’s comeback is unlikely to come anytime soon — pending some equine genetic rescue, that is.
Yet the example of the kunga as a hybrid species with outsize significance in the cultures that bred it would reverberate throughout history. Wolf-dog hybrids were intentionally bred as status symbols in societies including ancient Teotihuacan and eighteenth century Great Britain, while big cat hybrids like the liger and tigon have been the subject of both fascination and ethical complaints since at least the early 01800s. Some rarer hybrid species have shadowy histories, deeply linked with the black market exotic animal trade. Other hybrids result in negative consequences for the species they originate from. The Africanized honey bee, a cross between East African and European varieties of Apis mellifera, the western honeybee, was initially created in the 01970s as an attempt to breed a more docile bee that could withstand tropical temperatures. Instead, the bees broke out of their quarantine and spread throughout the Americas, serving as more aggressive competitors to the standard line.
Regardless of their precise impacts, the myriad forms of animal hybrid species that humans have created over the millenia have left a clear mark on our conception of the animal world. As biotechnologies like CRISPR-Cas9 gene-editing are refined and new techniques are developed, the world of intentionally bred hybrids will only get stranger. Yet all these hybrids can trace their (intellectual) ancestry to the kungas of Bronze Age Syria.
