The question has no single clean answer, because it depends on what you count as a disease and what you count as human. If you mean the oldest affliction found in any creature, cancer has been diagnosed in fossils from the age of dinosaurs. If you mean the oldest infection that has traveled with our own lineage, certain viruses appear to have been with us, or our primate ancestors, for millions of years. And if you mean the oldest disease identified through ancient DNA in anatomically modern humans, hepatitis B genomes have been recovered from remains dating back roughly ten thousand years. Each answer is defensible, and the competition between them reveals as much about the limits of scientific detection as it does about the diseases themselves.
Cancer Before There Were Humans
Cancer is not a modern invention. In 2020, researchers used CT imaging and tissue analysis to confirm an aggressive bone cancer, specifically an osteosarcoma, in the leg bone of a Centrosaurus apertus, a horned dinosaur that lived during the Cretaceous period, roughly 76 million years ago.1PubMed Central. CT and Histopathology Used to Diagnose Osteosarcoma in a Dinosaur The tumor was advanced enough that, had the animal not lived in a protective herd, it likely would not have survived as long as it did. This was not the first cancer found in a dinosaur fossil, but it was among the most rigorously diagnosed using the same methods a modern pathologist would use on a human biopsy.
Cancer, of course, is not a single disease caused by a single pathogen. It is a failure of cellular growth control that can arise in any complex organism with dividing cells. By that definition, cancer is as old as multicellular life itself. It predates humans, predates mammals, and predates the very concept of infection. Whether it qualifies as “the oldest disease” depends on whether you consider a category of cellular malfunction to be a disease in the way tuberculosis or malaria is a disease. Most researchers who study disease history draw a line between inherent biological errors and transmissible infections, and the more interesting contest takes place among the infections.
Viruses Written Into Our DNA
The deepest-reaching evidence for ancient disease comes not from fossils or ancient remains but from our own genome. Roughly 8% of human DNA consists of sequences left behind by ancient retroviruses that infected our ancestors’ reproductive cells tens of millions of years ago.2PubMed. Human endogenous retroviruses: our genomic fossils and companions These remnants, called endogenous retroviruses, represent more than four times as much genomic real estate as all our protein-coding genes combined. The original viruses are long extinct, but their genetic fingerprints persist in every human cell. By any reasonable definition, these were once diseases: they infected cells, hijacked DNA replication, and spread between hosts. They are also, by a wide margin, the oldest infections that left a verifiable molecular record in our lineage, even if the diseases they caused vanished millions of years before the first stone tool was chipped.
For viruses that still infect people today, herpes simplex holds perhaps the strongest claim to deep ancestry. Herpes simplex virus type 1 (HSV-1), the common cause of cold sores, appears to have co-evolved with the human lineage for around six million years, diverging alongside us from the lineage that led to chimpanzees.3PubMed Central. Evolutionary Origins of Human Herpes Simplex Viruses 1 and 2 Herpes simplex virus type 2 (HSV-2), more commonly associated with genital infections, has a stranger history. Molecular clock analyses suggest HSV-2 jumped from an ancestor of modern chimpanzees into an early member of the genus Homo roughly 1.6 million years ago.4Molecular Biology and Evolution. Evolutionary Origins of Human Herpes Simplex Viruses 1 and 2 A follow-up analysis using fossil distribution data and paleo-environmental modeling identified Paranthropus boisei, a robust-jawed hominin that overlapped geographically with early Homo in East Africa, as the most likely intermediate host through which the virus made the leap.5Virus Evolution. Network analysis of the hominin origin of Herpes Simplex virus 2 from fossil data The species barrier was likely crossed through hunting, butchering, or some other form of close physical contact with infected tissue.
If you consider HSV-1 a continuous companion of our lineage since its divergence from chimpanzees, herpes is plausibly the oldest still-active viral infection in humans. But this is an inference from evolutionary modeling, not direct evidence from ancient remains. The virus has no hard shell that fossilizes, and herpes DNA has not yet been recovered from ancient bones or teeth.
Bacterial Infections in Our Earliest Ancestors
Among bacterial diseases, the deepest physical evidence comes from a surprising source: the bones of Australopithecus africanus. Researchers examining a partial skeleton known as Stw 431, found in the Sterkfontein caves of South Africa and dated to roughly 2.5 million years ago, identified lesions on two lumbar vertebrae whose position, shape, and X-ray appearance were most consistent with early-stage brucellosis, a bacterial infection usually acquired from infected animals or their raw meat.6PLOS ONE. Possible Brucellosis in an Early Hominin Skeleton from Sterkfontein, South Africa This is not a certainty; diagnosing specific infections from bones millions of years old involves ruling out a long list of alternatives, and the authors were careful to frame their conclusion as a best-fit assessment. Still, if correct, it would place an identifiable bacterial disease in a pre-human hominin far earlier than any other candidate.
Tuberculosis is another strong contender for deep antiquity, though its timeline is harder to pin down. Molecular analyses of the tuberculosis bacterium’s family tree have used evolutionary modeling to estimate when the modern strains last shared a common ancestor, and those estimates vary widely depending on the method, ranging from thousands to tens of thousands of years.7PubMed. The Evolutionary History, Demography, and Spread of the Mycobacterium tuberculosis Complex What is clear is that the Mycobacterium tuberculosis complex includes strains adapted to a range of mammalian hosts, and its ancestor likely infected humans well before recorded history, possibly during the transition to settled agricultural life when close quarters with livestock and other people made transmission easier.
A different kind of revelation came in 2025 with the recovery of a 5,500-year-old genome of Treponema pallidum, the bacterium responsible for syphilis, yaws, and bejel, from a rock shelter in Colombia. The ancient strain turned out to be a sister lineage to all known modern subspecies, placing Treponema in the Americas millennia before European contact and before the subspecies that cause syphilis had even diversified.8PubMed. A 5500-year-old Treponema pallidum genome from Sabana de Bogotá, Colombia A companion study analyzing five pre- and peri-contact treponemal genomes from the Americas concluded that the evidence supports an American origin for all T. pallidum characterized at the genomic level, both ancient and modern.9PubMed Central. Ancient genomes reveal a deep history of Treponema pallidum in the Americas This reshapes the old debate about whether Columbus’s crews brought syphilis back to Europe from the New World: the pathogen’s roots in the Americas now appear much deeper than any single voyage, though the story of exactly which subspecies crossed the Atlantic and when remains unresolved.
Malaria’s Origins in African Apes
Malaria kills hundreds of thousands of people a year and has shaped human genetics more than almost any other disease, driving the persistence of sickle-cell trait, thalassemia, and other red blood cell variants that offer partial protection. Yet the deadliest human malaria parasite, Plasmodium falciparum, is relatively young in evolutionary terms. Genomic studies now show that P. falciparum emerged following a single cross-species jump from a gorilla parasite, possibly within the last ten thousand years.10PubMed Central. Ape Origins of Human Malaria That timeline upends earlier assumptions that P. falciparum had been co-evolving with humans and their ancestors for millions of years.
The second most common human malaria parasite, Plasmodium vivax, has a different and older backstory. It descended from an ancestral stock of parasites that circulated among chimpanzees, gorillas, and humans in Africa, and its relationship with humans predates the P. falciparum jump. The eventual spread of a protective genetic mutation, the Duffy-negative blood type, eliminated P. vivax from human populations in sub-Saharan Africa but allowed it to persist elsewhere.11PubMed Central. Out of Africa: origins and evolution of the human malaria parasites Plasmodium falciparum and Plasmodium vivax African apes harbor at least a dozen Plasmodium species, and the broader picture is one of repeated cross-species transmission events, with human malaria being just the most devastating branch of a much older parasite family tree.
Parasitic Worms and Ancient Guts
Not all ancient diseases require molecular clocks or fragile DNA. Intestinal parasites leave behind eggs that are remarkably durable, surviving in dried feces (coprolites) for thousands of years and visible under an ordinary microscope. This makes them some of the most directly observable diseases of the ancient world. Coprolites from the builders of Durrington Walls, a Neolithic settlement closely associated with Stonehenge and dated to around 2500 BCE, contained eggs from capillariid worms and fish tapeworm, found in both human and dog feces at the site.12PubMed Central. Intestinal parasites in the Neolithic population who built Stonehenge (Durrington Walls, 2500 BCE) The tapeworm eggs likely came from eating raw or undercooked freshwater fish, a detail that tells us something about the diet and cooking habits of the people who raised the monument.
In the Atacama Desert of South America, coprolites and mummified digestive tracts spanning 3,000 to 500 years before present yielded eggs from five different parasitic worm species, including pinworm, whipworm, and dog tapeworm.13Journal of Archaeological Science: Reports. Parasites in the Atacama Desert: New insights into the lifestyles of ancient human populations (3000–500 BP) The presence of dog tapeworm in human remains suggests close cohabitation with dogs, while pinworm, which spreads person-to-person through fecal-oral contact, tells us about hygiene conditions. These parasites are not as dramatic as plague or syphilis, but they were almost certainly far more common in daily life throughout most of human history, and their physical traces are among the easiest to identify in the archaeological record.
How Farming Changed the Disease Landscape
A recurring theme in disease history is that agriculture, for all its benefits, was a catastrophe for human health in several specific ways. Settling into permanent villages meant living in closer proximity to other people, to domesticated animals, and to accumulating waste. These conditions favored the transmission of respiratory infections, zoonotic diseases, and parasites. The oral microbiome offers a vivid example: studies of ancient dental calculus show that the agricultural revolution and later the industrial revolution drove the development of a more imbalanced oral microbial community and a rise in periodontitis, the chronic inflammatory gum disease that remains one of the most common conditions in the world.14Current Oral Health Reports. Evolutionary History of Periodontitis and the Oral Microbiota—Lessons for the Future
Research on ancient dental calculus spanning thousands of years has found that some microbial species, especially those involved in gum disease, appear to have been consistent features of the human mouth across history, while others linked to tooth decay or oral health have shifted with changes in lifestyle and diet.15PubMed Central. A Journey into the Evolution of Human Host-Oral Microbiome Relationship through Ancient Dental Calculus: A Scoping Review In other words, gum disease is not just old; it appears to be a stable, deep feature of human biology, while cavities are more of a cultural product, rising and falling with sugar consumption and grain-heavy diets. This distinction matters: periodontitis may be one of the genuinely oldest diseases that can be observed continuously in the human record, even if it rarely gets the attention that plague and smallpox attract.
Why Pinning Down “the Oldest” Is So Hard
The honest reason there is no consensus answer to this question is that the evidence gets worse the further back you look, and it gets worse unevenly. DNA degrades over time, and the rate of degradation depends heavily on temperature, moisture, and soil chemistry. A study of 158 radiocarbon-dated fossils from extinct New Zealand moa birds found that the average half-life of a short stretch of mitochondrial DNA in bone was about 521 years, and nuclear DNA degraded at least twice as fast.16PubMed Central. The half-life of DNA in bone: measuring decay kinetics in 158 dated fossils That does not mean DNA vanishes after a thousand years; under cold, dry, stable conditions, fragments survive for tens of thousands of years. But it does mean that the ancient DNA recovered from any given skeleton is short, damaged, and full of gaps, making it easier to detect pathogens that were present in large quantities (like a systemic blood infection) and much harder to find those that were localized to soft tissue.
This creates an unavoidable bias. Diseases that leave marks on bone, like tuberculosis, brucellosis, syphilis, and leprosy, are overrepresented in the archaeological record because bone survives. Diseases that kill quickly without affecting the skeleton, or that cause only soft-tissue symptoms, are largely invisible. A 2006 study that attempted to recover bacterial DNA from well-preserved museum bone specimens using highly sensitive methods found no reproducible evidence of surviving pathogen DNA, prompting the authors to caution that previous positive claims needed more rigorous verification.17PubMed Central. Evaluating bacterial pathogen DNA preservation in museum osteological collections The technology has improved since then, and genuine ancient pathogen genomes have been recovered in the years since, but the broader point holds: absence of evidence is not evidence of absence, and the diseases we can find in ancient remains are not a representative sample of the diseases that existed.
Ancient DNA molecules are typically just 30 to 60 base pairs long, the result of water-driven and oxidative damage that breaks the genome into progressively smaller fragments over time.18Current Biology. What Is the Oldest Disease Known to Humankind? There is also no simple relationship between how old a sample is and how much DNA survives; a 5,000-year-old tooth from a dry cave may yield better DNA than a 500-year-old bone from a damp churchyard. This variation is why new discoveries keep reshuffling the timeline. A pathogen genome recovered from a lucky specimen in favorable conditions can push a disease’s known history back by thousands of years overnight.
Hepatitis B and the Power of Viral Genomics
Hepatitis B has become a poster child for what ancient DNA can reveal when conditions cooperate. Researchers have now assembled full or partial hepatitis B virus genomes from human remains spanning roughly the last 10,500 years, including hunter-gatherers from Europe and South America who lived during the early Holocene.19PubMed. Ten millennia of hepatitis B virus evolution The most recent common ancestor of all known HBV lineages has been estimated to fall somewhere between about 20,000 and 12,000 years ago, and an earlier analysis placed the root of the HBV family tree between roughly 8,600 and 20,900 years ago with ancient genomes recovered from remains between about 800 and 4,500 years old.20PubMed. Ancient hepatitis B viruses from the Bronze Age to the Medieval period
These findings do not mean hepatitis B is the oldest human disease, but they represent the oldest directly recovered viral genomes from human remains. The distinction matters: herpes simplex is almost certainly older as an infection in our lineage, but that claim rests on evolutionary inference rather than physical viral DNA pulled from ancient bones. Hepatitis B’s success in the ancient DNA record is partly a matter of biology. The virus replicates to very high levels in the blood, circulates throughout the body, and its small, sturdy genome survives degradation better than the larger genomes of many other viruses. It is a case where the evidence reflects the virus’s properties as much as its actual antiquity.
Ancient Plagues That Left Genetic Scars
Yersinia pestis, the bacterium behind plague, was once thought to be a medieval problem, but ancient DNA has pushed its history deep into the Bronze Age. Researchers screening ancient remains across Eurasia identified early divergent strains of Y. pestis in individuals from Russia, Lithuania, Estonia, Germany, and Croatia dating to roughly 5,000 years ago.21Current Biology. Early Divergent Strains of Yersinia pestis in Eurasia 5,000 Years Ago These early strains lacked some of the genetic machinery that makes later plague so lethal, like the genes needed for flea-based transmission, suggesting that Bronze Age plague may have spread differently and caused different symptoms than the Black Death of the fourteenth century. The discovery of plague in widely separated populations across Eurasia at roughly the same time has even been proposed as a partial explanation for mysterious population collapses visible in the archaeological record of late Neolithic Europe.
Diseases do not just kill people; they leave marks on the survivors’ DNA. Studies of ancient human genomes have shown that interbreeding between modern humans and Neanderthals or Denisovans introduced genetic variants that now influence how our immune systems respond to infections, particularly viruses.22PubMed. Tracing the Evolution of Human Immunity Through Ancient DNA Some of those inherited variants appear to have been positively selected because they helped fight off pathogens, but they came with a cost: alleles that once conferred resistance to infections are now associated with increased risk for autoimmune and inflammatory disorders. In European populations, regulatory variants of Neanderthal origin have been found to be enriched among genes that respond to viral challenges, suggesting that archaic immune DNA was preferentially retained when it helped fight viruses.23Cell. Genetic Adaptation and Neandertal Admixture Shape Immune Responses to Pathogens One widely reported example is a stretch of Neanderthal-derived DNA on chromosome 3 that has been linked to susceptibility to severe COVID-19, a modern consequence of an ancient immune inheritance.24PubMed Central. New insights into human immunity from ancient genomics
Rare Genetic Disorders in Prehistory
The question of the oldest human disease usually focuses on infections, but genetic disorders are arguably older still, since they arise from mutations that can persist for as long as a gene exists. A vivid example emerged from the analysis of two female skeletons buried together in a cave in southern Italy more than 12,000 years ago. Ancient DNA testing revealed that both women were closely related, likely mother and daughter, and one carried two copies of a mutation in a gene involved in bone development. The genetic pattern matched acromesomelic dysplasia, an extremely rare inherited condition that causes severe short stature and markedly shortened limbs. The other woman carried a single copy of the same mutation, associated with a milder reduction in height.25New England Journal of Medicine. Ancient DNA solves 12,000-year-old mystery of rare genetic growth disorder Physical analysis of the skeletons had long suggested something unusual about their proportions, but it took modern paleogenomics to connect the dots to a specific gene and a specific diagnosis. Cases like this show that the tools used to find ancient infections can also identify non-infectious conditions, blurring the boundary between paleopathology and clinical genetics and hinting that many skeletal anomalies in museum collections may eventually get specific molecular diagnoses.