By Megan Shea
Cancer is a mutation within the DNA of a cell, which continues to replicate itself to a mass of cells containing the mutated genes (Greaves, 2002). While there is no specific cause of cancer, genetics and other environmental factors are proven causes for the disease. Cervical cancer is a special case as it is the only cancer that is caused by a viral infection.
The humanpapilloma virus (HPV) is a necessary factor in the development of cervical cancer (Dyer 2010). It has been linked with almost 99% of all cervical cancer cases (World Health Organization 2011). HPV-16 is the most common type of infection in the cervical cancer cases. HPV can be detected and treated before it develops into cancer. It does not show any symptoms of pre-cancerous lesions until 6 - 12 months after infection (Baseman & Koutsky 2005). HPV has survived and people have not evolved resistance to it because the virus does not have an impact on the reproductive rate since women who are infected by the virus that progresses into invasive cancer don't have any symptoms. The long time between onset of infection and carcinogenesis leaves women's reproductive rate without any disadvantages as they are still able to procreate. The only drawback is that women with cervical cancer don't live that long, but since evolution is not concerned with longevity -but reproduction- it is not a sufficient reason for natural selection to act upon.
The infection with human papillomavirus is a big factor in a persons' chances of getting cervical cancer but genetics do play a role as they increase a person’s likelihood of progression of HPV into carcinoma. The specific genes and proteins which cause cancer cannot be determined yet, but the Human Genome Project will be able to discover and answer those questions to give a better understanding (Greaves, 2002). A person’s ability to clear the infection on their own is their best way to not get cancer.
The infection with human papillomavirus is a big factor in a persons' chances of getting cervical cancer but genetics do play a role as they increase a person’s likelihood of progression of HPV into carcinoma. The specific genes and proteins which cause cancer cannot be determined yet, but the Human Genome Project will be able to discover and answer those questions to give a better understanding (Greaves, 2002). A person’s ability to clear the infection on their own is their best way to not get cancer.
Papilloma viruses (PV) have been found in many hosts throughout the past couple million years. There has been a lot of discussion over which hosts were the first to have the virus but there is evidence that shows that PV’s have been evolving along with its hosts for over 300 million years (Shah et al., 2010). There are three main groups of PV, two of which are shared with monkeys. Other strands of PV that humans have can also be seen in cows, dogs and horses.
Throughout the years, our medicine has evolved to rid many horrid diseases of the past. Social life has changed greatly throughout the years as well. The human body has adapted to the change of lifestyle but the genes inside have not changed as quickly. With the combination of the rapid change in social life and the not so quick changes of the genes, cancer has a greater chance of affecting people. The genes that have survived through survival of the fittest are now the ones that are giving cervical cancer a greater edge (Greaves, 2002). The genes that survived are having to work in different ways than they were before and cannot keep up.
Research has shown that HPV is a major cause for cervical cancer and there have been vaccines provided to prevent infection. HPV strands have adapted through the years to continue to infect and have gained an edge because there are still women becoming infected with cervical cancer. Almost 12% of cancers in females are cervical cancer (Burk, et al.).
Cancer is on a rise. The cases of cancer from 2007 to 2030 is expected to increase by 45% (World Health Organization). The increasing population as well as the increase in the lifespan of the population is allowing for more diseases to affect people more than they ever have. However, cervical cancer is one cancer that is highly preventable through a combination of HPV vaccines and Pap smears (CDC 2011; Rohan and Sha 2004) and its numbers can decrease further if these prevention strategies are implemented successfully.
Darwinian Principles
The principles are broken down according to Nesse and Wiliams (1996) into novel environments, evolution of virulence, trade-offs & compromises, and evolved defenses. Cervical cancer fits into these aspects as follows:
Novel Environments: The change in environments has allowed for the increase of cervical cancer. With adolescents reaching menarche and having sex at a younger age, HPV has a longer period of time to infect a person. Lifespans have continued to increase which allows for the virus to infect a person at a younger age and continue to stay in the body and affect it until cancer arises. People are living longer which is allowing the infection and disease to change the body more.
Evolution of virulence: For HPV to have a lower virulence, protected sex must occur. Since HPV is one of the most common STI’s, unprotected sex has increased its virulence and along with the medicines failing to protect against it has made certain strands of HPV very strong. HPV could have a low virulence but protected sex is very hard for someone to control and because of that there is a lessened chance to lower its virulence.
Trade offs & Compromises: Since every person wants to live longer they then have to deal with the consequences, or compromises they need to make with their bodies. If a person wants to live longer that gives their body more time to break down. In this case, it gives the body more time to for untreated HPV to advance to cervical cancer, a process that commonly can take decades (Baseman, Koutsky 2004).
Evolved Defenses: The body does not have any specific defenses against cervical cancer that a person would notice. The signs that people would notice is vaginal discharge and bleeding. These occur after the disease has already settled in. The body's DNA repair mechanisms try to fix the problem by stopping the mutations from happening within the cells. These mechanisms only come in place once the body already has cancer. Although this is not an obvious defense, it is a great one for the body to have. If the body can stop the mutation then the number of replicated cells containing the mutation decreases.
Conflicts: We are in constant fight with other organisms, such as papillomaviruses, which have co-evolved with us humans and other animal hosts for over 300 million years (Shah, Doorbar and Goldstein 2010). Since the co-evolution has taken place over such a long time period, the virus has been able to adapt to changes in its own environment and to those of its hosts. Therefore, it is hard for humans to become resistant to the virus.
