To prepare for future pandemics, scientists look to the past for clues. Over the last century, a series of new pathogens have swept the world, including H.I.V., Zika virus and SARS-CoV-2.

But the further back researchers look, the fuzzier that history becomes. Thucydides chronicled the plague of Athens, a disease that ravaged the city-state around 430 B.C. Despite all his gory details — “the inward parts, such as the throat or tongue, becoming bloody and emitting an unnatural and fetid breath” — today’s historians and scientists still don’t know which pathogen was responsible for it.

Three decades ago, geneticists conducting historical investigations started adding new clues like the bits of DNA that some pathogens leave behind in human skeletons. In recent years, the search for ancient disease genes has accelerated. On Wednesday, a team of scientists unveiled a new genetic chronicle, documenting the rise of 214 diseases across Europe and Asia over the past 37,000 years.

“The paper is large and sweeping and overall pretty cool,” said Hendrik Poinar, an expert on ancient DNA at McMaster University in Canada who was not involved in the study.

The researchers examined the remains of 1,313 ancient individuals for the project. The large scale enabled the researchers to do more than just push back the earliest known occurrence of different diseases. They could also track the rise and fall of epidemics across centuries.

The oldest remains the researchers studied belonged to hunter-gatherers. Their bones and teeth contained a host of pathogens, such as hepatitis B, herpes virus and Helicobacter pylori, a stomach-dwelling bacterium.

“As far back as we go, humans have had infectious diseases,” said Eske Willerslev, a geneticist at the University of Copenhagen and an author of the new study.

But those early remains did not have traces of some of the biggest killers of recent history, such as Yersinia pestis, the bacterium that causes plague.

Initially, Dr. Willerslev and his colleagues assumed that they would see such diseases rise to prominence starting about 11,000 years ago. That’s when people started domesticating animals, from which new diseases could spread more easily.

“This is the time when you’re in close proximity to animals, and you get these jumps,” Dr. Willerslev said. “That was the expectation.”

But the ancient DNA defied that expectation. The scientists found that plague and a number of other diseases jumped to people from animals thousands of years later, starting about 6,000 years ago. And those microbes did not jump into early farmers.

Instead, the new study points to nomadic tribes in Russia and Asia. Thousands of years after the dawn of agriculture, those nomads started rearing vast herds of cattle and other livestock.

Why diseases would have attacked those herders instead of earlier farmers, the scientists can’t say for sure. “We haven’t been able to come up with anything conclusive,” Dr. Willerslev said.

Martin Sikora, a geneticist at the University of Copenhagen and an author of the study, speculated that herds picked up diseases from rodents and other wild animals living on the steppes. “Maybe there was a big diversity of these agents around,” he said.

It’s also possible that nomadic herders were more vulnerable because they lived more closely with big herds of animals.

The nomads expanded over the next few centuries across the steppes of Asia and eastern Europe. In that time, their pathogens thrived; the scientists frequently found several individuals in a single grave with DNA from plague or other diseases.

Those epidemics were so intense that they changed the genetic profile of the nomads. Last year, Dr. Willerslev and his colleagues found that the nomads experienced a spike in mutations that boosted their immune system and that may have helped them resist the diseases they contracted. But their active immune systems may have also attacked their own bodies, producing chronic diseases such as multiple sclerosis.

These diseases might have played a part in Bronze Age history. In previous research, Dr. Willerslev and other scientists have found evidence that nomads expanded from the steppes of Asia into Europe about 4,500 years ago.

The study published on Wednesday suggests that the nomads may have gotten help from their pathogens. European farmers and hunter-gatherers had not evolved resistance to diseases such as plague and may have died off in huge numbers, making it easier for the nomads to move in.

“It has played a really big role in genetically creating the world we know of today,” Dr. Willerslev said of the possible spread of the pathogens.

Some of the diseases that the researchers tracked, such as plague, are familiar to us today. But others are more obscure. The scientists found that relapsing fever, a bacterial disease spread by lice, surged to high levels about 5,000 years ago. It became rare after a few centuries but didn’t disappear. After a few more centuries it reappeared and then continued going through long cycles of boom and bust.

It’s unclear what exactly drove such long-term changes, Dr. Poinar said. Epidemics of relapsing fever might have wiped out so many people that the microbe couldn’t find enough new hosts to infect. Once people recovered, it could return. But pathogens themselves were evolving at the same time, perhaps finding new ways to infect people.

“It’s a great start, but we all have miles to go before we sleep,” Dr. Poinar said.

The new chronicle of diseases has other limits. The technology that the Copenhagen team used can detect only DNA, but some of the worst pathogens, such as influenza and polio, are viruses that encode their genes in RNA.

The chronicle also has geographical limits. Archaeologists have traditionally focused their efforts on Europe and neighboring regions, so those are the places where Dr. Willerslev and his colleagues have found most of their ancient DNA.

“Africa would of course be super exciting, but we don’t have enough data,” Dr. Sikora said.

Discovering the drivers of diseases over thousands of years can help scientists prepare for future pandemics, Dr. Willerslev said. Some of our biggest enemies might be lying low at the moment, waiting to make a big comeback.

“If something has been successful in the past, it’s only a matter of time before it will reappear,” Dr. Willerslev said.