Some humans have tried to seek immortality in various ways since the earliest ages, lots of them even actually believed that after death, they will be resurrected in new bodies to live a new life. As stupid and childish as that may sound, can it actually be true? If we take a closer look at the biological processes in living creatures, the answer might not be that obvious.

Biologists have studied other life beings on our planet for hundreds of years by now. The more they discovered and studied, the more they were convinced with the idea of a life cycle that rules life on Earth. Every life being is born, either through sexual or asexual process, aims to survive and reproduce as much as possible, until the time comes when it dies and disappears from the world. This pattern seems to rule almost every living species on Earth, but it is not an absolute rule. Actually, there are cases where it is entirely broken, by a very weird phenomena called Biological immortality.

The phenomena of aging:

Aging seems to be one of the essential rules in the concept of life, it is something we learn so early after getting into the world that it is among the stuff we like to take for granted. However, it is in fact a complicated process that is still not completely understood to science. Several explanations are available at the moment, but none of them has attained a very widespread consensus in the academic community.

Normally, cells of most life beings doesn’t have the ability to divide beyond a certain amount of times. Body cells have to reproduce constantly in order to replace the dead and the old ones; and as you probably know, they do so through division. When a cell divides, it uses the data stored in the DNA at its core to create a new identical copy of itself. However, that copy is not absolutely ‘identical’, because each time a cell divide by two, little parts at the end of the DNA chain (called telmoeres) are lost forever. This means that incomplete data will be transferred into the next generation, and thus a slow decay will start among the genes of the cell. This is one of the primary sources behind what we call; Aging. Each time our cells reproduce, they will carry less practical data than they previously did.

According to a study published by America anatomist Leonard Hayflick in 1961, a regular cell can divide up to about 50 times before reaching a critical stage, where so much DNA data is lost that division reproduction is no longer possible. In his tribute, this characteristic is called Hayflick’s limit . When a certain cell reaches the Hayflick limit, it is going to be impossible to replace it with another spare. The cell will still be able to perform its normal metabolic activity as well as most of its biological functions, but it won’t produce any new generations to carry its duties further on. This is probably the primary reason why the vast majority of the life we know on our planet is a subject of aging, growing old, and finally dying. However, this rule doesn’t apply for every form of life on Earth. There are few weird exceptions that we know of, which are called; the biologically immortal species.

DNA shortening, even though a significant factor in aging, might not be the only cause. The ultimate factors in the aging process are still a subject of extensive research and they remain uncertain. One other popular theory is the DNA mutations, which attributes aging to types of DNA damaging factors that can lead to diseases like cancer.

Immortality in the animal kingdom:

A Biologically immortal being is a creature that will never die through senescence or natural aging; so as long as it doesn’t experience deadly accidents/diseases, it can practically live forever. Even though you might think that is impossible, it has been observed and studied in several species of both plants and animals. Some scientists are actually hoping to develop anti-aging drugs for human usage through researching the biology of these immortal creatures.

Turritopsis Dohrnii is a small species of jellyfish who possess this incredible ability. The cells of these primitive sea dwellers can undergo a process known as transdifferentiation, where old cells have the ability to transform into new adult cells directly, without going through any intermediate states. In other words, when those creatures start to age, they will simply revert to their polyp state, which is actually the first stage in their life cycle. Therefore, they will start to grow normally and re-experience their very same life cycle, in a pattern that can last for eternity. Furthermore, laboratory experiments have proven those jellyfish can revert to polyp state at any point in their life, even when they are still immature.

Another small ever-regenerating animal was identified rather recently; a very little freshwater dweller called Hydra. These simple and tiny creatures are evolutionary relatives of the jellyfish, but instead of living out in the open sea, they mostly prefer ponds and rivers. The scientific community had an increasing interest regarding these animals after a study published by Daniel Martinez in 1998 suggested they might have the immortality characteristic. However, they work in a little different way compared to the jellyfish.

Hyrda doesn’t change forms during its lifecycle; it starts its life as a polyp, and it stays a polyp ever after. When Hydras wants to reproduce, they can simply grow buds on the sides of their bodies which will develop into separate adult polyps later on. Those creatures have an ultimate regenerative ability: whether they lose a limb, get cut in half, or get broken into single cells in a test tube, each part of them will regrow into a mature complete functioning individual, or their disconnected cells will even reassemble into an intact creature. Hydra abuses this incredible regeneration potential to slow down or possibly stop aging completely. Every few days, the entire body of a Hydra will be replaced with fresh cells. With this speed of body replacement, it’s almost impossible for cells to accumulate risks of cancer or negative mutations. The longest study focused about aging in a particular Hydra population has been going on for about ten years now, and no signs of body growing old were detected. For such a very small animal, this time window is already a pretty long lifespan. Currently, many scientists believe this is yet another biologically immortal species.

Why do creatures reproduce?

By taking a closer look at the life pattern of immortal species, it is possible to build a new perspective about the life cycle of all living creatures. If you think about it, there are plenty of weird things regarding the biological reproduction process. What is the actual purpose of the whole reproduction thing? Why are animals so concerned to make offspring before they die? How come they had often favor the survival of their children over their own? One way to explain these questions might be that actually, reproduction is just a little of a different way to achieve the final objective of biological immortality.

All humans on the planet are created through sexual intercourse between their parents. We are simply made from a mixture of our parents’ genetic data. Those genetics may not include memories, but they include almost everything else; face look, eye color, and even personality traits. As we put it like this, it could be argued that, to some extent, all living creatures are modified clones of their parents. Some creatures, like mirco cells, will even simply make clones of themselves who carry their whole DNA data unaltered.

So, if the reproduction process in life is all about making clones, either if identical, altered, or improved, it might be that all life beings has the same strategy of biological immortality as jellyfish and hydra, just in a little more complicated way. Actually, mating and giving birth can be a mere empowered version of the immortality process in jellyfish. So, instead of countering aging, we just make clones/offspring who carry our genetic lines, so that we can keep our existence in the world. This process makes it possible for our descendants to evolve and develop improved traits, while keeping their main ancestral genetics.

Why did evolution choose not to erase aging?

If it is possible for a life being to develop the trait of biological immortality, why did very few species on Earth gain this ability over the course of their evolution? Before answering that, I have to clarify that in the beginning of this article, I have only explained one side of the scientific thoughts on the causes behind aging phenomena. Basically, what I pointed out was the process of cellular aging; the process through which a single cell grows old and finally dies. On the other hand, many scientists believe that several other causes might also play a huge role in the phenomena of aging.

For example, some arguments propose that creatures with a shorter lifespan but higher fertility rates at younger ages might have the evolutionary advantage over species with long lifespans but rather a slow development. Thus, the strategy of investing biological resources in producing offspring rather than constantly maintaining the body, might have proven more viable; as old individuals of the species will always bear high risks of dying through predation, accidents or diseases no matter how much resources were put into them beforehand. One proposed though controversial theory of aging, called the disposable soma theory states that living entities have a limited amount of energy that has to be divided between maintaining their body (‘soma’) and producing offspring, thus making aging an inevitable destiny if we are to give birth of children.

Although many people would view mortality as a burden, it might have been an evolutionary trait that we gained for our own greater good. Some scientists think that cellular senescence is essentially a technique we developed to counter cancer; because if a cell divides continuously it might accumulate several mutations to its DNA data, which can highly exposes it to the risk of gaining cancer.

There are few major theories currently proposed to explain why evolution, even though defined by Charles Darwin as a mechanism to help life forms live longer and reproduce more, did not actually help life in countering aging. First is Wear ans Tear, which suggests that, due to the laws of nature, it is physically and chemically impossible to keep someone living beyond a certain limit of time. That might be due to the continuous accumulation of damage through mutations, oxidization and other sources.

On the other hand, Medawar’s Hypothesis proposes that while natural selection should prefer species that reproduce more, living an extended life might be no longer a factor of evolutionary effect after someone has already produced offspring. Thus; sometime after reaching the age of sexual maturity, evolution is no longer concerned with how long or well a creature lives.

Non-Programmed aging theories, in a corresponding approach, concludes that aging after finishing the task of reproduction senescence might not affect evolution anymore, which makes aging irrelevant to natural selection. One example is the fact that aging is probably primarily caused by the accumulation of damage; so when a species experiences natural selection, it will only seek means to repair the damage limiting its reproduction capabilities, after which there might be little or no evolutionary motivation to support further survival of the individual. This is possibly represented by the various causes of death in humans; for the reasons explained above, our bodies has evolved to counter the risks of cancer and heart diseases at early ages only, but once we grow old and are finished reproducing, there is no need for our survival anymore, so we did not bother to evolve means that can resist these diseases further on in our lives.

A similar approach is suggested by the Programmed aging theories, which states that growing older to a particular extent actually carries some benefits to the overall population of a given species, while living beyond that limit might cause an evolutionary disadvantage for the species; thus implying that natural selection sets an optimum rate of aging for each organism. This way, living organisms may have some built-in mechanisms to regulate how fast they should age based on their surrounding environmental conditions, in order to provide them the best evolutionary benefits.

However, all of these theories face their own difficulties. The wear and Tear theory sails to explain why do we seem to be unaffected by any major physical or chemical factors early in our lives, while we surprisingly start experiencing them critically at later ages. Medawar’s Hypothesis makes a bit more sense, as it is natural to assume dying before an organism reaches puberty would stop its evolutionary line, and accordingly no organism should experience aging before reproduction. Non-Programmed aging theories are not actually mutually exclusive, and has trouble explaining several issues about aging process. Generally speaking, must aging theories are directly countered by the fact that biologically immortal species exists, which proves that aging might not be a necessary physical, chemical or natural phenomena.

On the other hand, such theories, if they prove to be actually significant on an evolutionary scale, should help to explain why we see very few biologically immortal species out there, and why most life on Earth is correspondingly ‘short aged’. Although this article highlighted some pretty weird immortal lifeforms, only few other ‘truly’ immortal creatures are known to us today. There must be some pretty good reasons why the mortal path was favored by the natural selection for our ancestors, rather than the precious eternal life that humans sought since the dawn of civilization.

Are we actually mortal? Well, in a way, you could argue that we are. But in another perspective, we could be only a form of our ancestors’ biological immortality.

Sources:

Absurd Creature of the Week: This Amazing Little Critter Just Might Be Immortal, The Wired.

Hydra as a Developmental Model.

Ageing, Hayflick limit, Wikipedia.

Biological Aging Theories, programmed-aging.org

Negligible Senescence,Non-Aging Species, programmed-aging.org

Maintenance and Repair Theories of aging, programmed-aging.orgn