Human papillomavirus has been infecting animals for at least 400 million years and has been co-evolving with humans since before our species existed as a distinct lineage. The virus itself is ancient, but our awareness of it is remarkably recent. Warts were recognized in antiquity, yet the virus behind them was not visualized until the mid-twentieth century, and the connection between HPV and cervical cancer was not proven until the 1980s. The full arc of HPV’s history spans geological time on one end and a still-unfolding story of vaccines and therapeutics on the other.
Hundreds of Millions of Years in the Making
Papillomaviruses are not a modern problem. Phylogenetic analyses estimate that the most recent common ancestor of the entire papillomavirus family dates back roughly 424 million years, well before any mammal walked the Earth. The viral genes most directly tied to cancer, E6 and E7, share a common ancestor going back at least 184 million years.1PubMed Central. Origin and evolution of papillomavirus (onco)genes and genomes These viruses have been found in mammals, birds, turtles, snakes, and even fish, suggesting that their evolutionary roots reach deep into vertebrate history.2bioRxiv. Ecological opportunity, radiation events and genomic innovations shaped the episodic evolutionary history of papillomaviruses New papillomavirus types continue to be identified in unexpected hosts, including a recently described virus in black-headed gulls, underscoring how widespread and diverse this viral family is.3PubMed. Identification of a novel papillomavirus in the migratory black-headed gull (Chroicocephalus ridibundus) from southwestern China
Over those hundreds of millions of years, papillomaviruses co-evolved tightly with their host species. They adapted to infect specific types of epithelial tissue, and this long mutual history produced the remarkable diversity of papillomaviruses we see today. Some types cause barely noticeable, chronic infections; others cause visible warts; and a smaller subset acquired the ability to drive cells toward cancer.4PubMed Central. Human Papillomaviruses; Epithelial Tropisms, and the Development of Neoplasia The point worth absorbing is that HPV did not suddenly appear in human populations. It has been with vertebrates for nearly as long as vertebrates have existed, and it was already infecting our hominin ancestors long before Homo sapiens emerged.
HPV and Our Hominin Relatives
The story gets more personal when you look at HPV16, the single type most strongly linked to cervical cancer. Genomic analyses of HPV16 variants suggest that the virus was already present in the common ancestor of Neanderthals, Denisovans, and modern humans. When those hominin lineages split from each other, the virus split with them. The divergence between HPV16’s major variant lineages, labeled A and BCD, happened roughly half a million years ago, which lines up with the timing of the Neanderthal-modern human split.5PubMed Central. Transmission between Archaic and Modern Human Ancestors during the Evolution of the Oncogenic Human Papillomavirus 16
Researchers have even found evidence that HPV16 lineages moved between archaic and modern human populations when those groups interbred. The most explanatory model indicates that ancestral HPV16 co-diverged with its hosts in parallel with the Neanderthal-Denisovan and modern human split, then later crossed back between the groups through sexual contact. Analysis of over 200 complete HPV16 genomes and thousands of partial sequences supports this timing, placing the divergence of the A and BCD lineages at roughly three times the age of modern Homo sapiens itself.6PLOS Pathogens. Niche adaptation and viral transmission of human papillomaviruses from archaic hominins to modern humans In other words, humans did not “catch” HPV at some identifiable moment in history. The virus was already there when we became human.
From Ancient Warts to Modern Science
People have known about warts for thousands of years. Ancient Greek and Roman physicians described skin growths that almost certainly correspond to what we now call common warts and genital warts. But for most of recorded history, nobody knew what caused them. The idea that warts were contagious circulated for centuries, and folk remedies abounded, but the viral origin remained invisible.
The first concrete steps toward understanding came in the twentieth century. In 1933, Richard Shope demonstrated that warts in wild cottontail rabbits were caused by a transmissible agent, a virus. The Shope papilloma became one of the earliest and most important animal models for understanding how a virus could cause a benign growth that sometimes progressed to cancer.7PubMed. The Shope papilloma-carcinoma complex of rabbits: a model system of neoplastic progression and spontaneous regression This was a landmark moment: for the first time, scientists had an experimental system showing that a papillomavirus could trigger cell growth that occasionally turned malignant.
The actual virus particles in human warts were first visualized by electron microscopy around 1949, though the findings at the time were described as being “at variance” with earlier observations of crystalline virus-like particles, reflecting how little was yet understood about papillomavirus structure.8Journal of Investigative Dermatology. Electron microscopic studies of the virus of human warts Scientists could see something in the wart tissue, but they did not yet have the molecular tools to classify or distinguish between different HPV types.
Connecting HPV to Cervical Cancer
The suspicion that cervical cancer might be linked to sexual transmission predated the identification of HPV by decades. By the mid-1970s, epidemiological evidence had made a strong circumstantial case. A key 1974 analysis laid out two competing hypotheses: one emphasizing early age at first intercourse, and the other emphasizing the number of sexual partners of both the woman and her husband. Mortality data showed a striking pattern: wives of unskilled laborers experienced cervical cancer rates about 181% of the average for married women, while wives of professional men experienced rates only 35% as high. The correlation between male syphilis rates and cervical cancer in their wives was pronounced, pointing toward a sexually transmitted infectious cause.9PubMed. Cancer of the cervix: a sexually transmitted infection?
But knowing that something sexually transmitted was involved did not identify the culprit. Herpes simplex virus type 2 was the leading suspect for years. The breakthrough came from the German virologist Harald zur Hausen, who pursued a then-unpopular hypothesis that papillomaviruses, not herpes, were responsible. In 1981, the DNA of HPV type 6 was successfully cloned from genital warts, revealing for the first time the existence of distinct HPV subtypes at the molecular level.10PubMed Central. Molecular cloning of viral DNA from human genital warts Zur Hausen’s laboratory then cloned HPV16 from a cervical cancer biopsy in 1983 and HPV18 in 1984. Those two types turned out to be collectively responsible for about 70% of all cervical cancers worldwide.11PubMed Central. Harald zur Hausen (1936 to 2023): Discoverer of human papillomavirus infection as the main cause of cervical cancer Zur Hausen received the Nobel Prize in Physiology or Medicine in 2008 for this work, decades after his initial hypothesis was met with skepticism.
How HPV Causes Cancer
Identifying which HPV types were present in cancers was only half the puzzle. Researchers still needed to understand how the virus actually drives normal cells toward malignancy. The answer centers on two viral proteins, E6 and E7, which target the cell’s own tumor-suppression machinery. E6 binds to and degrades p53, a protein that normally halts cell division when DNA is damaged and triggers cell death when damage is irreparable. E7 binds to Rb1, another key brake on cell growth. With both brakes disabled, cells lose control over DNA replication, DNA repair, and programmed cell death, creating the conditions for cancer to develop.12PubMed. Human papillomavirus E6 and E7: proteins which deregulate the cell cycle
This mechanism also explains why most HPV infections do not cause cancer. The vast majority of HPV infections are cleared by the immune system within a year or two. Cancer risk comes from persistent infections, and persistence depends on the virus’s ability to dodge immune detection. HPV has evolved several strategies for this, including keeping viral gene expression low in infected cells, interfering with the body’s immune signaling pathways, and manipulating how infected cells present themselves to immune surveillance.13PubMed Central. Evasion of host immune defenses by human papillomavirus The viral oncoproteins E5, E6, and E7 all play roles in regulating host immune responses, making persistent infection and immune evasion two sides of the same coin.14PubMed Central. Mechanisms of virus immune evasion lead to development from chronic inflammation to cancer formation associated with human papillomavirus infection The long gap between initial infection and potential cancer, often a decade or more, reflects this drawn-out battle between viral evasion and immune clearance.15PubMed Central. Papillomavirus Immune Evasion Strategies Target the Infected Cell and the Local Immune System
The Pap Smear, the Bethesda System, and HPV Testing
Long before anyone knew HPV existed, cervical screening was already saving lives. The Pap smear, introduced in the 1940s, became one of the most successful cancer prevention tools in medical history by catching abnormal cells before they became cancerous.16PubMed. Introduction of molecular HPV testing as the primary technology in cervical cancer screening: Acting on evidence to change the current paradigm But the system for interpreting results was a mess for decades. Laboratories used a jumble of inconsistent terminology: Pap class numbers that described nothing clinically meaningful, a three-tier dysplasia system with poorly reproducible distinctions, and frequent confusion between what was genuinely precancerous and what was a harmless HPV effect on cells.
The Bethesda System, introduced in 1988 and refined in subsequent updates, replaced this chaos with a two-tier framework for HPV-associated squamous lesions: low-grade and high-grade. The old distinction between an HPV-related cellular change and mild dysplasia, which had been driving unnecessary interventions, was collapsed into a single low-grade category. High-grade lesions, the ones that actually required treatment, got their own clear designation.17Acta Cytologica. The Bethesda System for Reporting Cervical Cytology: A Historical Perspective This was a direct consequence of the growing understanding that HPV was the underlying cause. The terminology could finally be organized around biological reality rather than morphological minutiae.
More recently, molecular HPV testing has begun to replace or supplement the Pap smear as the primary screening technology. Since HPV infection is a necessary precondition for cervical cancer, testing directly for the virus’s DNA offers higher sensitivity and the ability to identify risk before abnormal cells even appear. Large clinical trials and real-world implementation have provided strong evidence for this shift.16PubMed. Introduction of molecular HPV testing as the primary technology in cervical cancer screening: Acting on evidence to change the current paradigm
HPV Beyond the Cervix
For decades, HPV research focused almost exclusively on cervical cancer. But the virus also causes cancers of the anus, penis, vulva, vagina, and, in a development that caught many clinicians off guard, the throat. HPV-associated oropharyngeal cancer, affecting the tonsils and base of the tongue, has been rising in incidence, particularly among younger men with no history of heavy drinking or smoking, the traditional risk factors for head and neck cancer.18PubMed Central. HPV-associated head and neck cancer: a virus-related cancer epidemic HPV16 is responsible for the overwhelming majority of these oropharyngeal cases, and the trend has been described as a rising epidemic.19PubMed Central. HPV-Associated Head and Neck Cancer: Unique Features of Epidemiology and Clinical Management
The recognition of HPV as a cause of head and neck cancer is relatively recent and has shifted how these cancers are staged, treated, and discussed. HPV-positive oropharyngeal cancers tend to respond better to treatment and carry a significantly better prognosis than HPV-negative versions, which has prompted changes in clinical management. It also expanded the public health rationale for HPV vaccination from a women’s issue to one affecting everyone.
The Vaccine That Almost Did Not Happen
The key scientific breakthrough behind HPV vaccines was the discovery that the virus’s major outer protein, L1, spontaneously assembles into virus-like particles when expressed in laboratory systems. These particles look and behave immunologically like the real virus but contain no viral DNA, so they cannot cause infection. Clinical trials of vaccines based on these particles showed close to 100% efficacy in preventing persistent infection with the included HPV types and the precancerous lesions those infections cause. The first prophylactic HPV vaccines were licensed from 2006 onward.20PubMed Central. The HPV Vaccine Story
Population-level data since then have confirmed the vaccines’ real-world impact. In settings where at least 70% of the target population was vaccinated, particularly through school-based programs before sexual debut, HPV infections dropped by 58 to 100%, precancerous cervical lesions fell by 30 to 88%, genital warts declined by 60 to 90%, and invasive cervical cancer dropped by 70 to 88%.21PubMed. Population-level impact of HPV vaccination: a global systematic review of ecological, cross-sectional, and cohort studies Even studies looking at individual-level outcomes have found meaningful reductions in high-grade precancerous lesions among vaccinated women compared to unvaccinated women.22PubMed. Impact of human papillomavirus (HPV) vaccination on HPV 16/18-related prevalence in precancerous cervical lesions
Despite this success, the vaccine’s rollout was politically contentious in ways that had little to do with the science. Because HPV is sexually transmitted, vaccination of adolescents became entangled with debates about sexual behavior and parental authority. When the vaccine was recommended for boys in 2011, public attention was simultaneously hijacked by political controversies during a presidential campaign season, overshadowing the health message.23PubMed. Collateral Damage and Critical Turning Points: Public Health Implications of HPV Vaccine News Coverage for Boys and Men in 2011 Parental hesitancy has persisted, with research showing that parents who view the vaccine primarily through the lens of sexual transmission often report lower confidence in discussing it with their child’s doctor.24PubMed Central. HPV Parents’ stigmatizing beliefs about the HPV vaccine and their association with information seeking behavior and vaccination communication behaviors
Therapeutic Vaccines and What Comes Next
The existing HPV vaccines are preventive: they work by generating antibodies that block new infections but do not treat infections or lesions that already exist. For the millions of people already carrying persistent HPV or living with HPV-related precancerous changes, a different kind of vaccine is needed. Therapeutic HPV vaccines aim to stimulate the immune system’s cell-killing arm rather than its antibody-producing arm, training it to recognize and destroy cells displaying the E6 and E7 proteins that drive HPV persistence and cancer.25PubMed Central. Current state in the development of candidate therapeutic HPV vaccines
Several approaches are in clinical trials. DNA-based vaccines like VGX-3100 and GX-188E have shown strong immune responses and viral clearance rates as high as 78% among responders in phase II studies. Viral-vector vaccines, including MVA E2 and TG4001, have demonstrated the ability to trigger HPV-specific immune cell responses and promote regression of precancerous lesions. Peptide and protein-based vaccines have achieved partial results, though their effectiveness has varied depending on lesion severity and the specific immune makeup of the patient.26PubMed Central. Advances in Therapeutic Vaccines Against HPV: A Review of Human Clinical Trials None of these therapeutic vaccines has yet reached widespread clinical use, but the progress is real, and this remains one of the most active areas of HPV research.
The gap between preventive and therapeutic vaccination matters enormously for global health. Cervical cancer disproportionately affects women in low- and middle-income countries where screening infrastructure is weak and preventive vaccine coverage remains low. A therapeutic vaccine that could treat existing infections or early lesions would change the calculus for millions of women who have already been exposed. The science is still catching up to the need, but the decades-long trajectory from Shope’s rabbit warts to zur Hausen’s cloned HPV16 to today’s therapeutic trials shows how long and unpredictable the path from discovery to treatment can be.