Implications of cellular immortality

Evolution is an arms race, as proposed by most evolutionary models.

The mantra is "Survival of the Fittest" and it guides our understanding of why one trait may confer advantage and promote change in natural populations.

For many, this is taken to mean that there can be nothing alternate to the codified mechanisms.

But, 'the survival of the fittest' ignores the fact that the unfit may also survive.

Similarly, some may understand the mantra to imply that there is a single victor in the survival stakes, who stands astride the bodies of the vanquished with its claws in the air. But, It too shall die, just as dead as the rest. It is only a matter of time.

In truth, evolutionary success is about populations, not 'the survival of the fittest', but 'the fitment of the maximum population to survive'. Whoever gets the food and reproduces has decided advantage over those who don't.

In this way non-competition but cooperation of groups of organisms can have advantage over those that are mechanically 'the fittest'. And behavioural changes can occur far faster and more reactively than a trait change can spread from a mutated individual, through to a population.

So here we come to the crux of what I wish to discuss:

Most normal cells, in most of the organisms in the phylogenetic tree have programmed cell death (apoptosis). They are mortal and die after a certain time.

But cells exist that don't have a programmed end date but can still reproduce. We call them cancer cells or, if they are in vitro, immortal cells.

Surely in a population of single celled organisms, those that don't die but keep reproducing forever, would soon swamp the population that do die after a time. And all the same mutational, environmental and selection pressures would work on those immortal cells, just as much as on the mortal ones.

You'd still end up with predators and plants and more complex life forms, but all based upon immortal cells. They would still have the advantage over similarly traited mortal populations. Of course, there would be structural limitations upon what could be successful, far more than with mortal organisms.

But such immortal life forms, which we know can exist, are almost entirely absent from the phylogenetic tree.

Perhaps it is one of life's "rules of engagement"; hidden in the DNA.

Why would you give immortality to a creature that has already shown that it does not yet truly respect other life and the precious nature of the Earth?

Keep mixing up the genes. Perhaps some day, we would earn the right to enable it.

Great premise though, and I really wonder of the purposeful absence. It could also be that the planet might not be able to sustain a species like that...

originally posted by: charlyv
Perhaps it is one of life's "rules of engagement"; hidden in the DNA.

Why would you give immortality to a creature that has already shown that it does not yet truly respect other life and the precious nature of the Earth?

Keep mixing up the genes. Perhaps some day, we would earn the right to enable it.

Great premise though, and I really wonder of the purposeful absence. It could also be that the planet might not be able to sustain a species like that...

I think that, without doubt, cell apoptosis is a requirement of biological efficiency for very complex sexually replicating organisms. It allows for transitory structures to be discarded from the organism when they cease to be functionally efficient.

Definitely cells within our bodies which won't die are cancerous and they replicate and consume until they disrupt the balances of our biological machine, usually leading to death of the organism. So for us death is required for life.

Yet a simpler organism that simply didn't die would, and should, be predominant and should push into the upper branches of the tree of life by evolutionary process. Raw survivability trumps efficiency of organisation in pure population numbers.

Why it is absent is mysterious but most likely indicates that the processes of biological order have additional rules that we have not yet discovered.

I do think that immortal creatures should be so successful that they swamp the mortal ones and yet examples such as Planarian Flatworms and Immortal Jellyfish do not seem to do that. But they do evidence a complexity that must be the result of evolutionary process.

It is a mystery, at least for now.

a reply to: chr0naut

An immortal organism cannot evolve, it would fill it's niche in the ecosystem, thus competing with his own offspring. Eventually, a predator or disease would evolve to wipe the immortal creature that cannot evolve beyond this threat.

This is why aging and most sickness show up after the age of procreation with some margin to raise the offspring.

This is as simple as that.

a reply to: Cofactor

This is why aging and most sickness show up after the age of procreation with some margin to raise the offspring.

I think that is an effect, but not a cause. As age progresses, disease and sickness also have a higher probability of attacking you, exasperated by risks associated with inherited defects, life style and environment.

There's no way I want to be immortal. Certainly not in this body. This existence is driven by pain. Even the "pleasure" we manage to find is most often just a brief cessation of the grinding pain of wanting something like sex or food or sleep. Why would I want to continue with that forever?

Also, the longer we live, the more accidents play a greater part in our well-being and survival. So not only do I get the normal pain of existence, if I get in a car wreck or fall in the shower and bust something up (which is pretty much inevitable) that leaves me with painful, broken flaws - one on top of another - that I'll have to deal with forever.

I'll pass, thanks.

originally posted by: Cofactor
a reply to: chr0naut

An immortal organism cannot evolve, it would fill it's niche in the ecosystem, thus competing with his own offspring. Eventually, a predator or disease would evolve to wipe the immortal creature that cannot evolve beyond this threat.

This is why aging and most sickness show up after the age of procreation with some margin to raise the offspring.

This is as simple as that.

Most mutations are introduced at DNA replication as the cell divides. Immortal cells would be just as prone to replication errors as mortal ones. The result would be that the cell containing the replication error would be slightly genetically altered to the one not containing the error. So the processes of evolution would occur on immortal cells.

The existence of higher life forms that exhibit cell immortality, such as the Immortal Jellyfish and Planarian Flatworms, show order which must have arisen by evolutionary processes.

Indeed, genetic degradation over time would be worse for an organism that 'lives on' and mutation rates would rise as biological stability is threatened. This will probably lead to the eventual death of the majority of the mutant organisms but some would survive with new traits which may make them dominant. In that case, evolution could well be accelerated.

a reply to: chr0naut

Most mutations are introduced at DNA replication as the cell divides. Immortal cells would be just as prone to replication errors as mortal ones. The result would be that the cell containing the replication error would be slightly genetically altered to the one not containing the error. So the processes of evolution would occur on immortal cells.

Evolution work by trying "things" randomly, then filter the results to keep only the fittest. Nature lab is so huge that those randoms mutation tries an awfull lots of possibilities. The filter is death, the least performing are removed. Also your logic is circular, if immortal cells are still subject to random mutation, eventually one mutation will kill it, thus those cell are not immortal if random mutation are not repaired.

Evolution is similar to a Monte Carlos simulation, by using huge number of random test inputs, we can approach total testing for a system too huge to test completely.

originally posted by: Cofactor
a reply to: chr0naut

Most mutations are introduced at DNA replication as the cell divides. Immortal cells would be just as prone to replication errors as mortal ones. The result would be that the cell containing the replication error would be slightly genetically altered to the one not containing the error. So the processes of evolution would occur on immortal cells.

Evolution work by trying "things" randomly, then filter the results to keep only the fittest. Nature lab is so huge that those randoms mutation tries an awfull lots of possibilities. The filter is death, the least performing are removed. Also your logic is circular, if immortal cells are still subject to random mutation, eventually one mutation will kill it, thus those cell are not immortal if random mutation are not repaired.

During DNA replication, the polymerase reaction splits the double helix apart, forming two single strands and then reassembles the complement bases to each individual strand making up two separate double helix's.

It is during this 'rebuild' of DNA that errors are most likely to creep in to one or the other strand.

The double helix strands are then twisted up and packed into a far denser format that we identify as chromosomes. Each cell in the division gets one of the chromosomes from the pair.

For sexually replicating organisms there are two chromosomes per cell (dipoloidy) which complicates things but immortal cell division does not require (nor does it exclude) the genetic component from another chromosome (indeed cancer cells in our bodies are dipoloidal, containing two chromosomes per cell).

Replication errors would only affect one of the cells produced through such mitosis. It is only the mutated cell that would potentially die or evolve. The un-mutated 'sibling' cell would survive.

Evolution is similar to a Monte Carlos simulation, by using huge number of random test inputs, we can approach total testing for a system too huge to test completely.

I would suggest that it isn't that simple.

Observed evolution has always proceeded faster than the expected mathematical gradualism of such models, and in rapid 'steps' which has led to concepts such as punctuated equilibrium to try and explain it.

a reply to: chr0naut

Observed evolution has always proceeded faster than the expected mathematical gradualism of such models, and in rapid 'steps' which has led to concepts such as punctuated equilibrium to try and explain it.

Nice try. I understand why it was posted in creationism forum now... My bad. Sorry but ID is not one subject I wish to engage.

originally posted by: Cofactor
a reply to: chr0naut

Observed evolution has always proceeded faster than the expected mathematical gradualism of such models, and in rapid 'steps' which has led to concepts such as punctuated equilibrium to try and explain it.

Nice try. I understand why it was posted in creationism forum now... My bad. Sorry but ID is not one subject I wish to engage.

I made no mention of ID or Creationism or beliefs in the slightest.

Any such inference is your own.

Humans should not become immortal until we're capable of populating the universe. Earth can't handle a trillion people.

Most organisms on this planet are programmed to die. But nature doesn't object to reprogramming or else genetic engineering wouldn't be possible. If we could reprogram the telomeres to remain at the same length from birth, that would be a step towards immortality. But remember there are a lot of variables the toughest one being disease. No mater how long we live, we'll always be at risk for disease. Even if we could engineer the immune system to resist every disease we know, we still would be at risk for mutations and new diseases.

a reply to: chr0naut

But such immortal life forms, which we know can exist, are almost entirely absent from the phylogenetic tree.

I don't understand this - you mean there are organisms that are not included BECAUSE they're immortal? Even if an organism had the capability of immortality - for instance, an organism that was composed entirely of cancer cells - the chances of it actually living forever are statistically very slim (I would think - I don't have a number).

originally posted by: Phantom423
a reply to: chr0naut

But such immortal life forms, which we know can exist, are almost entirely absent from the phylogenetic tree.

I don't understand this - you mean there are organisms that are not included BECAUSE they're immortal? Even if an organism had the capability of immortality - for instance, an organism that was composed entirely of cancer cells - the chances of it actually living forever are statistically very slim (I would think - I don't have a number).

They are in the phylogenetic tree, but there are so few of them.

One would think that not dying would be the ultimate survivability trait. The Earth should be full of them.

In 1951, cancerous cervical cells were taken from a woman who died that same year. The immortal cancer cells are still alive and reproducing today. Called HeLa immortal cells after Henrietta Lacks, the woman they were taken from, they are still in use all over the world for experiments on living human cells.

Those cells, as long as they are fed nutrients and kept in an environment that allows them to metabolise, will quite literally live forever. So there is no reason to suggest that an organism based entirely on such 'cancerous' cells would not be able to outlive and out-survive other organisms.

I was not suggesting that creatures made from immortal cells cannot die, but they would have a decided advantage in the survival stakes. We know cancer is not uncommon and that cancer cells are immortal in that they have no programmed cell death. There should, therefore, be an abundance of organisms evolved from such cells.

a reply to: chr0naut

While researching the literature on HeLa cells, I came across this article which suggests that HeLa cells are a new species:

No Longer Human
By Lori Oliwenstein|Tuesday, December 01, 1992

discovermagazine.com...

From the article:

Lacks died in October 1951, but her peripatetic cells lived on. Now some biologists are saying that those cells, called HeLa cells for short, have lost more than their connection to Henrietta Lacks. HeLa cells, these researchers claim, are no longer human at all: they are single-celled microbes--closely related to us, to be sure, but their own distinct species.

How so, you ask? HeLa cells are not connected in any way to people, explains evolutionary biologist Leigh Van Valen of the University of Chicago. They have an extremely different ecological niche from us. They don’t mate with humans; they probably don’t even mate with human cells. They act just like a normal microbial species. They are evolving separately from us, and having a separate evolution is really what a species is all about.

The process of evolution is much the same for HeLas as it is for humans, although the former usually reproduce asexually, by cell division. As the cells divide, genetic mutations inevitably occur, and the ones that make the cells better adapted to their ecological niche--the petri dish-- are preserved by natural selection. When Henrietta Lacks’s cells first became cancerous, they also acquired the ability to survive indefinitely in a culture medium; that massive genetic transformation made them substantially different from ordinary human cells, and after four decades of evolution they have become more different still. Different strains of HeLa cells, analogous to different races of human beings, have even developed in some of the geographically separated lines.

While Van Valen is willing to name the new species, he is unwilling to suggest which higher taxonomic category it might fall into. Beyond the family name there are problems, he says. Since a HeLa cell can’t survive outside a culture medium, it obviously isn’t a primate in the usual sense. At the same time, says Van Valen, you can’t call it a protist- -a member of the kingdom of all single-celled organisms, which includes bacteria, protozoans, algae, and fungi--since that would mean that the same group had evolved twice, once sometime before 3.5 billion years ago and again today. It’s a fundamental tenet of evolutionary theory that evolution doesn’t repeat itself.

But that’s exactly what has happened, says Strathmann. And to him, HeLa cells are just a particularly aggressive and successful example of an evolutionary transition that has happened numerous times recently. Many cancer cells, in becoming cancerous, undergo the same type of genetic transformation that Henrietta Lacks’s cells did and thereby acquire the potential to be immortal; and many different lines of these cells are now surviving in petri dishes all over the world. All of them, according to Strathmann, have made the huge evolutionary leap from being metazoans-- multicellular creatures with organs and tissues--to being single-celled protists. What’s most amazing, he says, is how fast they did it: it took nearly 3 billion years for the first metazoans to evolve after life originated but just a handful of years for HeLa and other cell lines to take exactly the same step in the other direction.

As the article states, HeLa cells only survive in a petri dish. Could they evolve into an organism which doesn't require the media following the same path as other organisms which evolved out of the primordial soup?

I'm still searching through the literature - the complete genome was sequenced in 2013 - I'm sure there are researchers asking a lot of questions about the evolutionary trail of these cells.

a reply to: chr0naut

Immortality goes against evolution and doesn't really offer a big advantage in long term survival. Death / extinction is one of the biggest factors that determines which organisms survive in the long term, and leads to more diversity of genes. Evolution is about passing down genes. As long as an organism can survive long enough to do this, the rest of its life doesn't matter to evolution. The organisms that spread the most genes are the ones that are the most successful, but if they don't die, they are just passing the same stagnant genes down over and over, which means less genetic diversity in the long run. Diversity of genes is a key factor in long term survival, so there is no reason why immortality should become a dominant factor with any species as you suggested.

I also don't think that it's valid to compare modern cells today in multi cellular creatures to single celled organisms of the past. I don't see any reason why ancient single celled creatures would become immortal and not go extinct.

Those cells, as long as they are fed nutrients and kept in an environment that allows them to metabolise, will quite literally live forever.

See what you did there? As long as they are fed and kept in the SAME environment, they can live for long times, but how would these organisms survive a major environment change? They won't. They'll die off immediately and become extinct. Genetic diversity is important for this reason. If you don't have enough genetic diversity to survive a big change in their niche, they die off. Scientists are keeping them alive in their ideal environment.

So there is no reason to suggest that an organism based entirely on such 'cancerous' cells would not be able to outlive and out-survive other organisms.

In the short term you are right, but we are talking about ability to survive long term and adapt to big changes. It's not just about one organism living longer than another. That literally has no evolutionary benefit. Cancerous cells also kill many people while they are too young to reproduce, so you have to consider that. They don't benefit long term survival or genetic diversity at all.

a reply to: chr0naut

Everyone is immortal until they aren't.

Que Sera, Sera...

a reply to: Barcs

See what you did there? As long as they are fed and kept in the SAME environment, they can live for long times, but how would these organisms survive a major environment change? They won't. They'll die off immediately and become extinct. Genetic diversity is important for this reason. If you don't have enough genetic diversity to survive a big change in their niche, they die off. Scientists are keeping them alive in their ideal environment.

True immortality would mean resistance to all the variables in nature that could kill a life form. That would be an entirely different evolutionary scenario than the one we experience on this planet. It would be analogous to bacteria that become immune to antibiotics but on a whole new scale. A truly immortal organism would have the ability to resist any challenge to its existence.

As you said, immortal cells are only immortal when they are in their own environment. But as I asked in my post, could HeLa cells evolve to step out of the petri dish? Even if they did, it wouldn't matter because they would still be at risk for multiple challenges in their new environment.

What we're really talking about here is extending life either by means of the evolutionary trail or artificially through human intervention.

There is no "immortal" in this universe unless you believe in a god.

originally posted by: Barcs
a reply to: chr0naut

Immortality goes against evolution and doesn't really offer a big advantage in long term survival. Death / extinction is one of the biggest factors that determines which organisms survive in the long term, and leads to more diversity of genes. Evolution is about passing down genes. As long as an organism can survive long enough to do this, the rest of its life doesn't matter to evolution.

But immortal cells continue to replicate. They don't do it once, or a few times, and then cease like mortal cells.

With every replication, there is a possibility of mutation which will make one replicated cell genetically different from the other, just like with mortal cells.

Most mutations will usually kill the cell but some will survive and may confer advantageous traits not in the sibling cell. That successful mutated cell itself then can replicate, carrying the mutation into new replicated cells. This means that genetic variation is likely to occur at similar rates to mortal cells and would, under situations of natural selection, lead to evolution as the less fit are eliminated.

Also, in comparison to mortal cells, the populations of immortal cells would bloom far more rapidly, causing a resource contention which would swamp mortal cells. This 'fight for food' would negatively affect the immortal cells too, but it wouldn't necessarily cause their extinction as not all cells would starve.

No doubt, cannibalistic predator cells would evolve and then populations would stabilize at a point fairly close to the maximum biomass that an environment could support. Also, some cells would have mutations which allow survival beyond the boundaries of their initial environment, this spreading into alternate adjacent environments gives sufficient barriers to even allow for speciation.

Evolutionary process would still continue and so changing environments could be accommodated in exactly the same way we see in mortal cells.

The organisms that spread the most genes are the ones that are the most successful, but if they don't die, they are just passing the same stagnant genes down over and over, which means less genetic diversity in the long run. Diversity of genes is a key factor in long term survival, so there is no reason why immortality should become a dominant factor with any species as you suggested.

I also don't think that it's valid to compare modern cells today in multi cellular creatures to single celled organisms of the past. I don't see any reason why ancient single celled creatures would become immortal and not go extinct.

Those cells, as long as they are fed nutrients and kept in an environment that allows them to metabolise, will quite literally live forever.

See what you did there? As long as they are fed and kept in the SAME environment, they can live for long times, but how would these organisms survive a major environment change? They won't. They'll die off immediately and become extinct. Genetic diversity is important for this reason. If you don't have enough genetic diversity to survive a big change in their niche, they die off. Scientists are keeping them alive in their ideal environment.

So there is no reason to suggest that an organism based entirely on such 'cancerous' cells would not be able to outlive and out-survive other organisms.

In the short term you are right, but we are talking about ability to survive long term and adapt to big changes. It's not just about one organism living longer than another. That literally has no evolutionary benefit. Cancerous cells also kill many people while they are too young to reproduce, so you have to consider that. They don't benefit long term survival or genetic diversity at all.

I suppose it depends on your definitions of cellular immortality too. I define it as a genetic trait that blocks normal cell apoptosis. Immortal cells can die almost as easily as mortal ones, it is just that they won't die without a damn good reason, or because it is 'their time to die'.

I have also not taken into account telomeric shortening and other ageing related issues but, in the immortalised cells that we do have and study, we have not really (to my knowledge) seen these issues arising.