Now, an international and interdisciplinary team of researchers led by geneticists from Trinity College Dublin and zooarchaeologists from LMU Munich and the Bavarian State Collections of Natural History (SNSB) has deciphered the prehistoric cultural trajectory of this species by analysing 118 genomes recovered from archaeological bones dating across 12 millennia and stretching from Mongolia to Ireland.

The earliest sheep-herding village in the sample, Aşıklı Höyük in central Türkiye, has genomes that seem ancestral to later populations in the wider region, confirming an origin in captures of wild mouflon over 11,000 years ago in the western part of the northern Fertile Crescent.

By 8,000 years ago, in the earliest European sheep populations, the team found evidence that farmers were deliberately selecting their flocks — in particular for the genes coding for coat colour. Along with a similar signal in goats, this is the earliest evidence for human moulding of another animal’s biology and shows that early herders, like today’s farmers, were interested in the beautiful and unusual in their animals.

Specifically, the main gene the team found evidence of selection near was one known as “KIT,” which is associated with white coat colour in a range of livestock.

Also by that time, the earliest domestic sheep genomes from Europe and further east in Iran and Central Asia had diverged from each other. However, this separation did not last as people translocated sheep from eastern populations to the west.

First, in parallel with human cultural influences spreading out from the early cities of Mesopotamia we see sheep genomes moving west within the Fertile Crescent around 7,000 years ago.

Second, the rise of pastoralist peoples in the Eurasian steppes and their westward spread some 5,000 years ago profoundly transformed ancestral European human populations and their culture. This process changed the makeup of human populations, for example, altering the ancestry of British peoples by around 90%, and introduced the Indo-European language ancestor of the tongues spoken across the continent today.

From the dataset used in this study it now seems that this massive migration was fuelled by sheep herding and exploitation of lifetime products, including milk and probably cheese, as it is around the same time that sheep ancestries are also changed. Consequently, by the Bronze Age, herds had about half their ancestry from a source in the Eurasian steppe.

Dr Kevin Daly, Ad Astra Assistant Professor at UCD School of Agriculture and Food Science and an Adjunct Assistant Professor in Trinity’s School of Genetics and Microbiology, is the first author on the research article that has just been published in leading international journal Science. He said: “One of our most striking discoveries was a major prehistoric sheep migration from the Eurasian steppes into Europe during the Bronze Age. This parallels what we know about human migrations during the same period, suggesting that when people moved, they brought their flocks with them.”

Dan Bradley, leader of the research and Professor of Population Genetics in Trinity’s School of Genetics and Microbiology, said: “This research demonstrates how the relationship between humans and sheep has evolved over millennia. From the early days of domestication through to the development of wool as a crucial textile resource, sheep have played a vital role in human cultural and economic development.”

Joris Peters, co-corresponding author, Professor of Paleoanatomy, Domestication Research and the History of Veterinary Medicine at LMU Munich and Director of the State Collection for Paleoanatomy Munich (SNSB-SPM), said: “Our study, while convincingly reconciling morphological and genomic evidence of the geographic origin of domestic sheep, clearly illustrates that further transdisciplinary research is needed to clarify the patterns of dispersal and selection of the many landraces occurring today in Eurasia and Africa.”

“A recent global health report revealed that oral diseases — such as untreated tooth decay and gum disease — affected 3.5 billion people in 2022, making them the most widespread health conditions,” said study lead author Souvik Sen, M.D., M. S., M.P.H, chair of the Department of Neurology, Prisma Health Richland Hospital and the University of South Carolina School of Medicine in Columbia, South Carolina. “We aimed to determine which oral hygiene behavior — dental flossing, brushing or regular dentist visits — has the greatest impact on stroke prevention.”

The Atherosclerosis Risk in Communities (ARIC) study, one of the first large-scale investigations of this kind in the U.S., assessed the home use of dental floss through a structured questionnaire of more than 6,000 people. Among those who reported flossing, 4,092 had not experienced a stroke, and 4,050 had not been diagnosed with an irregular heartbeat known as atrial fibrillation (AFib).

Participants were asked about their status regarding high blood pressure, diabetes, high cholesterol, smoking, body mass index, education, regular brushing and dentist visits. During the 25 years of follow-up, 434 participants were identified as having strokes, of which 147 were larger artery brain clots, 97 were heart-driven clots and 95 were hardening of the smaller arteries. Additionally, 1,291 participants were noted to have experienced AFib.

The analysis found:

• Flossing was associated with a 22% lower risk of ischemic stroke, 44% lower risk of cardioembolic stroke (blood clots traveling from the heart) and 12% lower risk of AFib.
• The associated lower risk was independent of regular brushing and routine dental visits or other oral hygiene behaviors.
• Increasing the frequency of flossing had a greater chance of stroke risk reduction.
• Flossing was also associated with a lower chance of cavities and periodontal disease.

Researchers were surprised by the reduction of irregular heartbeats, or AFib. AFib is the most common form of irregular heartbeat. It can lead to stroke, heart failure or other cardiovascular complications. More than 12 million people are projected to have AFib in the United States by 2030, according to the American Heart Association’s 2025 Heart Disease and Stroke Statistics.

“Oral health behaviors are linked to inflammation and artery hardening. Flossing may reduce stroke risk by lowering oral infections and inflammation and encouraging other healthy habits,” Sen said. “Many people have expressed that dental care is costly. Flossing is a healthy habit that is easy to adopt, affordable and accessible everywhere.”

Study limitations include that data were based on answers to a questionnaire, and the 25-year follow-up appears to have focused on stroke and heart outcomes only. There was no follow-up concerning flossing or other oral behaviors over the years, Sen said.

“This study offers more insights into the specific dental health behaviors that may be linked to stroke risks and potential risk reduction. With further research, dental health practices could possibly be incorporated into the “Life’s Essential 8″ risk factors, which include diet, physical activity, nicotine exposure, sleep, body mass index, blood pressure, blood glucose and blood lipids,” said Daniel T. Lackland, Dr.P.H., FAHA, American Heart Association EPI and Stroke Council member and professor of epidemiology and director of the Division of Translational Neurosciences and Population Studies in the department of neurology at the Medical University of South Carolina in Charleston. Lackland was not involved in this study.

Study background, and details:

• The study began in 1987 and is ongoing.
• Of the 6,258 participants, 82% were self-reported white adults and 18% Black adults. Their average age was 62 years and 55% were women.
• Potential participants were excluded if they had total tooth loss, dental implants, heart disease, organ transplant, artificial joints, implanted heart valve or stent or major surgery.

“At first, these findings seemed to introduce a paradox: If scratching an itch is bad for us, why does it feel so good?” said senior author Daniel Kaplan, M.D., Ph.D., professor of dermatology and immunology at the University of Pittsburgh. “Scratching is often pleasurable, which suggests that, in order to have evolved, this behavior must provide some kind of benefit. Our study helps resolve this paradox by providing evidence that scratching also provides defense against bacterial skin infections.”

Allergic contact dermatitis is an allergic reaction to allergens or skin irritants — including poison ivy and certain metals such as nickel — leading to an itchy, swollen rash. Succumbing to the often-irresistible urge to scratch triggers further inflammation that worsens symptoms and slows healing.

To figure out what drives this vicious cycle, Kaplan, first author Andrew Liu, student in Pitt’s Medical Scientist Training Program, and their team used itch-inducing allergens to induce eczema-like symptoms on the ears of normal mice and those that don’t get itchy because they lack an itch-sensing neuron.

When normal mice were allowed to scratch, their ears became swollen and filled with inflammatory immune cells called neutrophils. In contrast, inflammation and swelling were much milder in normal mice that couldn’t scratch because they wore tiny Elizabethan collars, similar to a “cone of shame” that a dog might sport after a visit to the vet, and in animals that lacked the itch-sensing neuron. This experiment confirmed that scratching further aggravates the skin.

Next, the researchers showed that scratching causes pain-sensing neurons to release a compound called substance P. In turn, substance P activates mast cells, which are key coordinators of inflammation that drive itchiness and inflammation via recruitment of neutrophils.

“In contact dermatitis, mast cells are directly activated by allergens, which drives minor inflammation and itchiness,” explained Kaplan. “In response to scratching, the release of substance P activates mast cells through a second pathway, so the reason that scratching triggers more inflammation in the skin is because mast cells have been synergistically activated through two pathways.”

Mast cells are culprits in a range of inflammatory skin conditions and allergic reactions, but they’re also important for protecting against bacteria and other pathogens. As such, the researchers wondered if scratching-induced activation of mast cells could affect the skin microbiome.

In experiments led by coauthor Marlies Meisel, Ph.D., assistant professor of immunology at Pitt, the team showed that scratching reduced the amount of Staphylococcus aureus, the most common bacteria involved in skin infections, on the skin.

“The finding that scratching improves defense against Staphylococcus aureus suggests that it could be beneficial in some contexts,” said Kaplan. “But the damage that scratching does to the skin probably outweighs this benefit when itching is chronic.”

Now, the researchers are investigating new therapies for dermatitis and other inflammatory skin conditions such as rosacea and urticaria that suppress inflammation by targeting receptors on mast cells.

Other researchers on the study were Youran Zhang, Chien-Sin Chen, Ph.D., Tara N. Edwards, Ph.D., Torben Ramcke, M.D., Lindsay M. McKendrick, Eric S. Weiss, Jacob E. Gillis, Colin R. Laughlin, Simran K. Randhawa, Catherine M. Phelps, Kazuo Kurihara, M.D., Ph.D., Hannah M. Kang, Sydney-Lam N. Nguyen, Jiwon Kim, Tayler D. Sheahan, Ph.D., Sarah E. Ross, Ph.D., and Tina L. Sumpter, Ph.D., all of Pitt and UPMC; and Sumeyye Ozyaman, of Pitt and Istanbul Medipol University.

This research was supported by the National Institutes of Health (T32NS73548, T32CA0820840, R01DK130897, U24EY035102, K99NS126569, R01AR071720 and R01AR077341) and the German Research Foundation.