Civilization as we know it would not exist without domesticated animals. However, the domestication of these creatures has also brought humanity a host of serious diseases that have repeatedly escalated into epidemics and pandemics.
This is highlighted by a new study from an international team of researchers led by geogeneticist Martin Sikora from the University of Copenhagen. Recently, they found direct evidence that the onset of animal domestication and livestock breeding coincided with spikes in diseases transmitted from animals to humans, such as the plague (Yersinia pestis) and relapsing fever (LBRF).
Archaeologists have long suspected that when nomadic hunter-gatherers in Eurasia began forming large pastoral communities around 12,000 years ago, the risk of pathogen transmission from animals to humans increased. Now, modern methods of ancient DNA analysis have helped scientists confirm this hypothesis.
What the Researchers Discovered
The scientists analyzed 405 billion DNA sequences collected from 1,313 ancient human remains across Eurasia. This allowed them to identify numerous genes belonging to microbes.
The team gathered enough details to create a 12,500-year chronicle of the emergence and spread of major human diseases. The authors of the study stated that a significant portion of these microbes originated from external sources, such as animals.
It turned out that many of the microbes infecting humans remained stable throughout the sampling period. Zoonotic diseases, where pathogens are transmitted from animals to humans, were found in human remains dating back about 6,000 years. This period is considered a turning point from hunter-gatherer societies to agricultural societies.
The team also discovered a significant accumulation of zoonotic microbes in human remains across Eurasia that were around 5,000 years old. This spike in diseases indicates that during this time, steppe herders migrated to new regions, bringing with them not only new agricultural knowledge but also diseases transmitted by domesticated animals.
The researchers noted that the rise in zoonotic disease incidence is not solely a result of direct interactions between humans and animals. It may also be linked to the fact that as population density increased in communities, local hygiene conditions worsened, and the number of rodents, fleas, lice, and ticks increased. For instance, outbreaks of relapsing fever have historically correlated with poor living conditions and hygiene.
Animal Domestication and Human History
Today, zoonotic diseases account for over 60 percent of re-emerging infectious diseases. However, several millennia ago, these microbes were a completely new experience for people, according to Science Alert.
The researchers believe that prehistoric societies in the Eurasian steppes, which were exposed to zoonotic pathogens earlier than others, had significant advantages. These advantages included not only access to regular sources of meat and milk but also ample time to adapt to new animal pathogens.
The team asserts that further research is needed to better understand the nature of these disease outbreaks. However, scientists have already provided compelling evidence that the domestication of animals was a significant shift in human lifestyle that led to the spread of zoonotic infections. Overall, animal domestication has had a profound impact on global health and the history of humanity.
The results of the study were published in the journal bioRxiv.