HPV, which stands for human papillomavirus, refers to a group of more than 200 related viruses. HPV is very common and spreads through skin-to-skin contact during sexual activity with another person who has the virus. Most sexually active people have some type of HPV infection at some point in their lives. In some cases, HPV can lead to cancer and other serious health issues. Understanding where HPV originally came from can provide important context on how these viruses spread and evolve.
The Evolutionary Origins of HPV
Like all viruses, HPV has evolved over very long periods of time. Scientists believe that papillomaviruses like HPV first emerged tens of millions of years ago. These ancient papillomaviruses likely infected early mammals and evolved along with their hosts over evolutionary timescales. The papillomavirus family itself contains a remarkably diverse collection of viral types that can infect a wide range of mammal species including humans.
Research indicates that papillomaviruses have been coevolving and speciating along with their mammalian hosts for at least 80-100 million years. Major HPV types that specifically infect humans are estimated to share a common ancestor that existed around the time of the origin of the human species, at least 500,000 years ago. This means that HPV viruses are very ancient and have been circulating in human populations and adapting to our species for hundreds of thousands of years.
Host Specificity of HPV Viruses
A key feature of papillomaviruses like HPV is their high degree of host specificity. This means that they can usually only replicate in the cells of one or a few closely related host species. For example, canine and rabbit papillomaviruses cannot infect humans. The human papillomavirus strains have specifically evolved to infect human cells and take advantage of features of human anatomy for transmission. HPV viruses cannot naturally jump between highly divergent hosts like humans and non-primate mammals.
Within the papillomaviruses found in a single host species, different viral strains can evolve to target different tissues and cause varied pathologies. The diversity of HPV strains infecting humans likely reflects their long co-evolutionary history with our species as they adapted to survive in different human niches.
Genital HPV Types Emerged Early in Human Evolution
Researchers have analyzed HPV genome sequences and mutation rates to estimate when different major virus groups emerged. This molecular clock analysis indicates that the ancestor of the main genital HPV types arose around 500,000 years ago. This was around the estimated time when the Homo genus first emerged. This suggests that HPV strains specialized for infecting human genital tissues already existed by the time the first early humans evolved.
In particular, the branch of the HPV family tree containing types HPV16 and HPV18 appears to be one of the oldest and most successful viral lineages. HPV16 and 18 together are responsible for around 70% of cervical cancer cases. Their ancestral relationship indicates these high-risk genital HPV types evolved early and have maintained transmission in humans over hundreds of thousands of years.
Patterns of HPV Co-Evolution with Humans
By examining the evolutionary relationships between papillomavirus strains infecting different hosts, researchers have outlined three major patterns of virus-host co-evolution that help explain HPV origins:
Codivergence
Codivergence refers to parallel viral and host evolution, in which virus and host lineages speciate in sync. Codivergence has occurred over millions of years between mammals and their papillomaviruses. This is evidenced by related virus types infecting closely related hosts. For example, similar HPV variants are found in humans and other primates.
Host Switching
Host switching happens when a virus jumps from one host species to another. This allows papillomaviruses to expand into new host niches. Scientists believe episodes of host switching have allowed animal papillomaviruses to cross over into humans on rare occasions. For example, some analyses suggest the high-risk genital type HPV16 may have originated in a cross-species jump from ancient proto-chimpanzees to archaic humans around 1.6 million years ago.
Viral Speciation
Viral speciation occurs when an existing virus adapts and diversifies into new strains within the same host. This is the primary driver of new HPV type emergence within humans. Ongoing viral evolution and selection pressures cause new papillomavirus lineages to arise that are adapted for infection of specific tissues and cell types within the same host.
Geographic Origins and Spread of HPV
Examining the present-day geographic diversity and distribution of HPV variants provides clues about the virus’s origins and early evolution in human populations. Key patterns observed include:
Africa
Africa has the highest overall HPV genetic diversity globally. This suggests modern humans already carried diverse HPV strains when migrating out of Africa around 100,000 years ago. Africa also displays greater diversity of the high-risk genital HPV strains compared to other regions, indicating these viruses evolved early in ancestral African populations.
Indigenous Populations
Indigenous peoples in remote regions often have unique HPV strain variants not found elsewhere. This includes populations like tribes in the Amazon and Orang Asli in Malaysia. Their unique viral variants likely reflect extended isolation and HPV evolution in place from the earliest human settlers.
Viral Lineages Related to Ancient Human Migrations
Phylogenetic analyses reveal that the relationships between HPV variants reflect ancient human migration routes. Closely related strains are found in geographically distant populations that descended from common ancestors. For example, similar HPV16 sublineages are present in European and North American populations, reflecting origins from early Eurasian migrants.
Mechanisms of HPV Transmission and Persistence
To understand HPV origins, it is also important to consider how the viruses are able to reliably spread and persist long term. Key factors include:
Transmission Through Skin Contact
HPV viruses are shed from infected skin and mucosal surfaces and transmit through surface-to-surface contact and microscopic abrasions. This allows the viruses to pass between sexual partners and from mother to newborn child.
Latent Infections
HPV frequently establishes latent low-level infections that persist for decades. Viral genomes integrate into host cell DNA and can remain dormant inside cells for long periods before reactivation.
Immune Evasion
HPV viruses have evolved mechanisms to evade host immune detection. They reduce antigen presentation and cytokine signaling to escape elimination by the immune system.
Mutation and Adaptation
Frequent mutations allow HPV strains to diversify and develop variations better adapted for infectivity and persistence. This enables them to spread widely and avoid population extinction.
Conclusion
In summary, human papillomaviruses like HPV originate from papillomavirus lineages that have coevolved with mammals over tens of millions of years. Genital HPV strains arose early in human evolution and have continued diversifying and spreading globally as long-term viral companions of our species. Ongoing evolution and adaptation to the human host underlie the persistence and prevalence of HPV worldwide.