Cancer is a group of diseases that emerges as a result of failures in regulatory mechanisms involved with cell division. This fatal disease always has a strong relationship with the process of evolution. In contrast to the other diseases, the process of cancer development mirrors the process of evolution of species. Also, except for childhood cancers, other types of cancers can escape selective pressure as those are limited to the old ages of organisms. Therefore, it looks like Cancer plays and is trying to cheat the process of evolution that was deadly for most of the defective mechanisms!
Introduction
Evolution is the process that a species improves its adaptive characteristics to the environment over several generations. During the evolution of a species, each individual acquires new variations in their genetic material compared to their parents and other individuals. Those different variations in genetic material result in various physical characteristics called phenotypes. These phenotypes are either more or less advantageous to the individual to adapt to the environment for its survival and reproduction. If the individual has more advantageous characteristics over other individuals, the individual obtains more favourable conditions for survival and a higher chance to be involved in reproduction passing its more adaptive genes to the next generations is called Natural Selection. Under natural selection, any individual has to compete with individuals of their species and other species facing selective pressure. Ultimately, Evolution is a natural process that increases the abundance of beneficial genetic patterns that help the organisms to properly adapt to the environment and opposite for the disadvantageous genetic patterns.
Cancer is a result of failures in the regulation of cell division. Cell division should occur only if it is necessary and beneficial for the survival of the whole organism. If the cell division takes place unnecessarily then it can be disadvantageous than the benefit of the functions of that cells. Therefore cell division should be tightly regulated by several mechanisms. Tumour is an abnormal mass of cells that have an inadequate regulatory mechanism in cell division. All of these regulatory mechanisms involved in cell division are controlled under the information given by several types of genes. Therefore mutations in those genes may result in Cancers.
How cancer development mirrors the process of species evolution
As individuals of a species are ruled by the evolutionary process under natural selection, individual cells of tissue can be ruled through the normal evolutionary process. Those individual cells can acquire mutations during the cell division and those mutations can lead the cell to obtain different characteristics compared to other cells. Those different characteristics can be either advantageous or disadvantageous to adapt the microenvironment of those cells in the host tissue. If the individual cell has obtained necessary mechanisms to get more advantages over other cells in processes such as gathering nutrition and oxygen and if the cell has effective mechanisms for surviving against the body’s defence system, this cell can grow well and make clones of cells that have the same characteristics, through cell division. Now those cells can grow into a mass of over proliferated cells called a tumour. This tumour has the potential to develop into a malignant (cancerous) tumour if the evolution of that clone of cells occurs until those cells acquire all the essential gene mutations to perform the process of Metastasis by which cancer spreads into nearby and distant tissues. If the clones of cells fail to acquire the essential mutations to perform metastasis, the tumour would either be suppressed or remain as a benign tumour (non-cancerous tumour). During the evolution of the tumour, as the initial step, one individual cell acquires a few mutations in the genes that perform a critical part in the regulation of cell division. Those mutations should fit for the survival of the cell against the body’s defence system. Usually, these mutations occur in the genes which promote or reduce the rate of cell division and repair gene mutations. After these mutations, the individual cell can reproduce a clone of cells that contain the same mutations. As the next step, those cells grow and reproduce rapidly in the tissue over normal cells similarly the individuals of a species with strong adaptive characteristics survive and reproduce passing those characteristics to their offspring. Then the portion of this abnormal cell mass in the host tissue becomes higher with time. Meanwhile, those abnormal cells can acquire more mutations that can lead to further beneficial characteristics for rapid proliferation. Then the portion of the mass of cells with more mutations becomes higher with time over normal cells and the cells with a few mutations. In this way, tumour cells can acquire more mutations one by one and the cells with more mutations can increase the number of cells and percentage of cells in the host tissue with the same characteristics over other cells that contain no or a few mutations. At the advanced stages, cells get the ability to be detached from the host tissue, travel through the blood and lymph vessels to distant locations surviving from the immune system, and develop on other tissues under varied conditions similarly that the species evolved to successfully adapt to the different environmental conditions. Therefore, while other types of diseases are struck by the evolutionary process, it seems like Cancer takes benefits using the evolutionary process.
Influence of Cancer in the process of evolution
Since just the early stages of the evolution of multicellular organisms, it is compulsory to develop proper mechanisms to tightly regulate cell division and maintain the proper structure and function of the parts of the organism as the organism can not get the advantages of multicellularity without properly regulating cell division. Therefore, since the very first stage of multicellularity, under natural selection, only the multicellular organisms who had appropriate mechanisms to properly regulate the cell division would be able to survive and reproduce. During evolution, all multicellular organisms have evolved necessary mechanisms to avoid Cancer. Some of these mechanisms are suppression of cell division, induction of apoptosis (programmed cell death), DNA damage repair, and inhibition of metastasis. Those mechanisms have evolved in those species through natural selection in which only the organisms that have effective mechanisms to avoid cancer have survived and reproduce, passing those characteristics to the next generations. Therefore Cancer has been incredibly involved in determining the characteristics of species during the long process of evolution of the species. Also, cancer has partially escaped the selective pressure limiting usually into old ages after the effective reproduction periods of the organisms. Therefore, an individual with strong adaptive characteristics and containing gene mutations that can lead to an increased risk of cancer can survive and reproduce at his/her young age passing those mutations into next generations. Childhood cancer is an exception for this above mentioned escaping character of Cancer. Some hypotheses explain childhood cancer as childhood cancer remains for generations as the cost of innovation to develop protective mechanisms for tumour suppression is greater than the benefit that can be achieved from it for the species.
Conclusion
During the long process of evolution, cancer has affected incredibly to determine the genetic variation of all the multicellular species. Also, the process of cancer growth can be explained using the theory of evolution. Understanding Cancer through an evolutionary perspective would lead to solving unexplainable problems that exist in cancer biology.
References :
- Casás-Selves, M., & DeGregori, J. (2011). How Cancer Shapes Evolution and How Evolution Shapes Cancer. Evolution: Education and Outreach, 4(4), 624–634. https://bit.ly/3rK74Dj
- Sun, W., & Yang, J. (2010). Functional mechanisms for human tumor suppressors. Journal of Cancer, 1(1), 136–140. https://bit.ly/3ybNjqK
- The genetic basis of cancer | Colombo Beacon Blog. (2020). https://bit.ly/3yjY36v
- What Is Cancer? – National Cancer Institute. (n.d.). Retrieved July 31, 2021, from https://bit.ly/2VohT20
- What is evolution? | Facts | yourgenome.org. (n.d.). Retrieved July 30, 2021, from https://bit.ly/3fheusH
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