It is a beautiful day in the warm spring. The vibrant flowers bloom, the kaleidoscopic butterflies dance in the light breeze. It is just like every other spring. You’re going on a walk in the park with your beloved grandmother; an old park, one which has accompanied you through the years of your childhood. And with every passing year, you notice more and more how the paint on the swing that you used to love is turning achromatic, and the gear connected to the chain is creaking due to the friction; there’s a lack of lubricant to smooth the movement.
There is something different about this day. You notice that your grandmother walks a little slower, and her smile brings about a new fold that you’ve never seen on her face before. It is positioned right beside her dimple, where you usually give her a kiss. Today, you realise that the park is not the only thing that has fallen victim to time.
When we think of immortality, we think of living forever, eternal life, essentially an unending existence.¹ As a biology student, immortality has been one of the most fascinating ideas to me. Whether it is morally and ethically correct is still debatable, but the science behind it all: is it possible? Can we, mere humans, achieve eternal living? Rather than looking at the philosophical aspect of immortality, I am intrigued to know more about the technicalities and today, I will be looking at it from a biological perspective.
Diving into this matter, what we need to know first is this: why do people die? According to the CDC list of leading causes of death in 2020, diseases such as heart disease and cancer dominate the chart, bringing about over half of all deaths.² Other factors that perpetuate death are, of course, accidents and injuries. However, hypothetically speaking, if you managed to live a healthy life in a completely danger-free environment, you would still die of old age.
When we talk about achieving immortality in science, our focal point is limiting the effect of ageing or stopping ageing completely. Let us dig deeper into the science behind ageing. Our cells are continuously dividing. As I type this article (and as you read this), millions or even more of our body cells are working hard to divide in a process called mitosis.³ This is vital, as it has many functions in order to keep us healthy: replacing damaged and dead cells, growth, on the whole keeping our body functioning efficiently.
Figure 1; Mitosis. Plantlet. https://plantlet.org/wp-content/uploads/2020/04/cell-division.jpg.
Figure 2. Life Sciences Cyberbridge, Harvard University. http://cyberbridge.mcb.harvard.edu/mitosis_4.html.
In the cell cycle, before a cell goes into the mitosis phase (where the cell actually divides), it has to go into what we call the replication phase where the chromosomes (the most important components of the cell that contain all of the genetic information) replicate. This is because in the process of mitosis, two identical daughter cells will be produced, both having the same number of chromosomes as the parent cell. Unfortunately, during the replication stage, the chromosomes are not replicated exactly, in that the ends of the chromosomes are continuously getting shorter and shorter as they replicate more and more. This is because the DNA at the very end of the chromosome cannot be fully copied in each round of replication. As every single specific letter in our DNA is vital for life, even if a tiny little bit of the end is cut off, it can wreak havoc in our system. Cells could die, turn into cancer cells or lose their ability to replicate.
The good news is, we have a mechanism that stops our cells from completely dying each time they divide, and that saviour of ours is called the telomere! Telomeres are little caps at the ends of our chromosomes; they contain no important genes or information so it is completely safe for them to be removed during chromosome replication. In spite of that, we now encounter another problem when attempting to achieve immortality: the telomeres will eventually wear off, exposing the parts of the chromosomes that carry the important information. When this happens, it is game over for our cells and the scenario that was mentioned in the previous paragraph will occur.
Figure 3: Chromosomes and telomeres. Yourgenome. https://www.yourgenome.org/sites/default/files/illustrations/diagram/chromosome_telomere_TTAGGG_yourgenome.png.
Now, would you believe me if I said that that is what ageing is, fundamentally? Scientists believe that ageing is the shortening of our chromosomes, which is the reason our physical health deteriorates as we age. As our body cells keep on dividing, a gradual degradation of our body occurs, resulting in ageing. Our body is not made to live forever. This is also the reason why ageing is the main risk factor for diseases such as cancers, heart diseases and opportunistic infections.⁴ As our cells lose the ability to efficiently divide, the likelihood that we will be struck by disease increases. Our body becomes too weak to fight infection and our cells are at risk of experiencing the accumulation of damaged DNA over time. With the other environmental factors at play, there is no way for us to survive if our body keeps on degenerating.
How does this relate to immortality? In theory, if we managed to stop ageing, we could live forever, because we’d stop our cells from going haywire.⁵ This does not mean we need to stop our cells from dividing, but rather, we need to find a way to ensure that all the chromosomes that carry vital information are replicated for mitosis. Stem cells are an example of cells that have vanquished the problem of the loss of genetic information as they have the ability to divide indefinitely because of a mechanism that keeps their telomeres in check. Basically, a stem cell can fix its telomeres every time they shorten.
Figure 4: Hydra vulgaris. Encyclopedia of Life. https://content.eol.org/data/media/7e/bb/37/542.16624195064.jpg.
Hydra vulgaris, an organism that is biologically immortal,⁶ has unlocked immortality using stem cells. The hydra’s apparent immortality and capacity to regenerate is due to the presence of three distinct stem cell lineages: ectodermal and endodermal epithelial stem cells, and interstitial stem cells.⁷ In other words, the stem cell in the hydra has given it its ability to be biologically immortal and it all goes back to the fundamental component of cell division; the telomere.
Since the genesis of humanity, immortality has been a fictional fantasy, a mythological tale, a puzzle that we have striven to find answers to. The oldest living woman in the world is currently 119 years old. This is light years away from the life expectancy of the earliest living humans in the Palaeolithic age, which was 25-35 years. Retracing our evolution, this has been made possible due to incredible medical and technological advances. Are we destined to continue exceeding our life expectancy?
Can we be immortal?
References:
Immortality Definition & Meaning. (2022, March 21). Merriam-Webster. https://www.merriam-webster.com/dictionary/immortality
FastStats - Leading Causes of Death. (2022, January 13). CDC. https://www.cdc.gov/nchs/fastats/leading-causes-of-death.htm
Starr, M. (2021, January 23). Your Body Makes 3.8 Million Cells Every Second. Most of Them Are Blood. ScienceAlert. https://www.sciencealert.com/your-body-makes-4-million-cells-a-second-and-most-of-them-are-blood
Niccoli, T., & Partridge, L. (2012, September 11). Ageing as a risk factor for disease. PubMed. https://pubmed.ncbi.nlm.nih.gov/22975005/
O'Brien, J. (n.d.). The Science of Immortality Archives. John Templeton Foundation. https://www.templeton.org/discoveries/immortality-research
Wetzel, C. (2021, December 13). How Tiny, 'Immortal' Hydras Regrow Their Lost Heads. Smithsonian Magazine. https://www.smithsonianmag.com/smart-news/were-closer-to-understanding-how-immortal-hydras-regrow-lost-heads-180979209/
Bosch T.C.G. (2008) Stem Cells in Immortal Hydra. In: Bosch T.C.G. (eds) Stem Cells. Springer, Dordrecht. https://doi.org/10.1007/978-1-4020-8274-0_3
Fosbery, R., Taylor, D., Gregory, J., & Jones, M. (2020). Cambridge International AS & A Level Biology Coursebook with Digital Access (2 Years) 5ed. Cambridge University Press.