Darwin re-visited

[Kayra]

Hey folks.

 

Has anyone noticed (way to many pages to search back through) that cancer is a perfect example of every aspect of evolution?

 

Initial mutation of the cell division braking system to allow hyper-reproduction is required to start the process

Past that, the cancer community has to:

• Suffer death from internal and external signals ordering apoptosis (selective pressure to bypass/disrupt/disable varied mechanisms)
  
• Turn off or dial down genetic repair to allow mutations.
  
• Suffer predation (selective pressure to evade predation) from leukocytes.
  
• Suffer lack of resources (Selective pressure to both exist with limited resources, and eventually evolve means to get the resources via angiogenesis)
  
• Diversify. (This is why mature cancers are resistant to Chemo)
  
• Cooperate: (Only a few cells need express angiogenesis signals for all to benefit, while others can mimic cell types the immune system ignores)
  
• Eventually the community spawns pioneer cells that travel to other parts of the body. Most fail outside of the community, but constant mutation eventually allows others to take root.
  

Those that due are practically perfectly suited to continue the process, and that is when things turn bad.

 

Watching the process would almost inspire one to believe there was a "Design" in play, and yet it all falls logically in place given the circumstances.

 

Am I way out there?

[CraigD]

Has anyone noticed (way to many pages to search back through) that cancer is a perfect example of every aspect of evolution? ...

A problem with this idea is that, unlike diseases caused by living pathogens (eg: bacteria or parasites) or quasi-living pathogens (eg: viruses), individuals of the “cancer community” aren’t organism. Cancer cells are genetically identical to their host, where rather than differentiating from other cells in the usual, beneficial way (eg: forming specialized tissues, organs, limbs, etc.), they reproduce uncontrollable, causing disease by impairing the function of non-cancerous cells. Parasites, bacteria, and viruses are almost – genetically entirely distinct from their hosts – almost, because some portions of host DNA appear to have been inserted by pathogens, especially viruses (recall that viruses must insert their DNA or RNA into host cells DNA or organelles, as by definition they can’t metabolize on their own).

 

So, while it’s somewhat accurate to say “cancer has evolved”, it’s inaccurate to consider it as being species distinct from its hosts. Cancer in humans and other animals that are susceptible to it is part of these host species evolution, not of “species of cancer” that have coevolved with their hosts, like parasites and other genetically distinct pathogens. Though pathogens can (but don’t always) cause cancer, such pathogens are not themselves cancer. Cancerous tumors are genetically part of their hosts, as much as are their other tissues.

[Kayra]

Hey Craig :hyper:

 

I was referring to the cancer showing all of the aspects of evolution, not that the cancer was a separate life form.

 

The cells themselves can be considered the organisms, genetically differing from the host in a small way initially, and in far more drastic ways as it evolves. (Since the host locks down mutations in its normal cells). The genetic similarities though, are not the point I was trying to make, nor must they be genetically different to cause an evolutionary effect (Excluding disabling the inherently anti-evolutionary growth/mutation braking systems).

 

The fact that they reproduce uncontrollably, invade other tissues, or cause disruption is not really relevant either. Man, as a community of organisms, does the same to our environment.

 

Again, I had not intended to present cancer as a separate species :rolleyes: (Although it does have most of the characteristics of a parasite)

[maikeru]

Hey folks.

 

Has anyone noticed (way to many pages to search back through) that cancer is a perfect example of every aspect of evolution?

 

Initial mutation of the cell division braking system to allow hyper-reproduction is required to start the process

Past that, the cancer community has to:

• Suffer death from internal and external signals ordering apoptosis (selective pressure to bypass/disrupt/disable varied mechanisms)
  
• Turn off or dial down genetic repair to allow mutations.
  
• Suffer predation (selective pressure to evade predation) from leukocytes.
  
• Suffer lack of resources (Selective pressure to both exist with limited resources, and eventually evolve means to get the resources via angiogenesis)
  
• Diversify. (This is why mature cancers are resistant to Chemo)
  
• Cooperate: (Only a few cells need express angiogenesis signals for all to benefit, while others can mimic cell types the immune system ignores)
  
• Eventually the community spawns pioneer cells that travel to other parts of the body. Most fail outside of the community, but constant mutation eventually allows others to take root.
  

Those that due are practically perfectly suited to continue the process, and that is when things turn bad.

 

Watching the process would almost inspire one to believe there was a "Design" in play, and yet it all falls logically in place given the circumstances.

 

Am I way out there?

 

No, you're not. I thought the same thing when I studied and worked in an undergrad cancer research lab and took several classes on immunology, and it changed my perspective on evolution.

 

Although CraigD has a good point about cancer cells being a part of and derived from the host, I would strongly correct his wording of "genetically identical to the host" and say "almost genetically identical to the host"--and it's in that "almost" wherein the distinctions between a cancerous and noncancerous cell are made. Overall, are the percentage or numbers of changes small relative to the size of the genome? Sure. But small changes in code or control can lead to drastic and serious changes and consequences when they happen in the right spots of the genome or affect gene regulation that will in turn affect cell differentiation, division, growth, and function.

 

I'm always fascinated by the ways that nature can tweak species. One of the most stunning examples, IMO, is this:

 

Small eagle ancestor (LUCA of Haast's and the Little Eagle) --> Haast's Eagle

 

BBC NEWS | Science/Nature | Huge eagles 'dominated NZ skies'

 

What they showed was that the New Zealand bird was in fact related to one of the world's smallest eagles - the little eagle from Australia and New Guinea, which typically weighs less than 1kg (two pounds).

 

PLoS Biology: Ancient DNA Provides New Insights into the Evolutionary History of New Zealand's Extinct Giant Eagle

 

Prior to human settlement 700 years ago New Zealand had no terrestrial mammals—apart from three species of bats—instead, approximately 250 avian species dominated the ecosystem. At the top of the food chain was the extinct Haast's eagle, Harpagornis moorei. H. moorei (10–15 kg; 2–3 m wingspan) was 30%–40% heavier than the largest extant eagle (the harpy eagle, Harpia harpyja), and hunted moa up to 15 times its weight. In a dramatic example of morphological plasticity and rapid size increase, we show that the H. moorei was very closely related to one of the world's smallest extant eagles, which is one-tenth its mass. This spectacular evolutionary change illustrates the potential speed of size alteration within lineages of vertebrates, especially in island ecosystems.

[Pyrotex]

Keep in mind that biological evolution -- Darwinian Evolution (DE) -- absolutely requires genetic diversity within the population of similar individuals, and the passing of genetic material from one generation to the next, and a process of Selection that determines which individuals get to pass on their genes.

 

Any OTHER kind of biological change which does not conform to this blueprint may be "change", it may even be said to be "evolution" in some sense, but it cannot be biological DE.

 

So, do your cancer cells fit this blueprint?

[maikeru]

Keep in mind that biological evolution -- Darwinian Evolution (DE) -- absolutely requires genetic diversity within the population of similar individuals, and the passing of genetic material from one generation to the next, and a process of Selection that determines which individuals get to pass on their genes.

 

Any OTHER kind of biological change which does not conform to this blueprint may be "change", it may even be said to be "evolution" in some sense, but it cannot be biological DE.

 

So, do your cancer cells fit this blueprint?

 

Genetic diversity in cells of the body is created through, for example, mutations and copy and repair errors in most somatic cells that gradually accumulate and accumulate in different cells and lineages, because replication and repair are inherently imperfect, and as a part of controlled hypermutation, recombination, and selection in immune cells such as B-cells and T-cells to creative diversity and selectivity in the variable regions of their antibodies or TCRs.

 

Somatic hypermutation - Wikipedia, the free encyclopedia

 

Those resultant and surviving immune cells are not genetically identical to other somatic cells. They have had their coding in specific regions changed. They are now genetically distinct cellular individuals within the greater human individual. These immune cells have genetic diversity. It is a key component of our adaptive immune systems.

 

Errors mount as we age and cell replicate and repair themselves, telomeres become shorter, different cells, different tissues, different organs are exposed to different stresses, toxins, etc. that may affect the integrity of the cells in those places and their cellular genomes, and the immune system gradually loses its capability to distinguish and maintain the consistency and homogeneity of most somatic cells through killing and fighting cells that are damaged, potential trouble, or eventually openly rebellious as we age (or perhaps contributes to aging?). CraigD mentioned that somatic cells are "genetically identical to the host" but this is not strictly and technically correct. In fact, we are a multiplicity, a community of mostly almost genetically identical cells. There's a big difference between "almost" and "are" genetically identical.

 

IMO, from the viewpoint of a microbiologist, immunologist, or oncologist, the individuals and actors of Darwinian evolution are not higher organisms like plants or animals, but the viruses, bacteria, protozoans, and yes, even the cells of an individual's body, which form communities and collectives. What are the populations? The resultant cellular lineages and their descendants, some of which may accumulate deleterious changes in their genetic code that could lead to "abnormal" behavior and cellular division and reproduction (neoplastic cell lineages, i.e., cancer), but in truth, they are only trying to maximize their reproductive success and survival and compete for limited resources, space, etc., which unfortunately comes at the expense of the individual and the greater collective and community of cells that make up the human individual. What are the selective pressures? The immune system, the tumor microenvironment, other cells nearby or faraway, exposure to chemicals or toxins or environmental insults such as those in chemotherapy, foods, hormones, UV light, etc.

 

Though the evolution of a population in an ecosystem and cell lineages in a body rely on the same basic process, there are a few key differences between selection at these different levels. First, whole organisms reproduce much more slowly than individual cells do. This means that while the evolution of a new species or a major transition (such as the evolution of birds from dinosaurs) may take millions of years, the evolution of a cell lineage into a cancerous form can take place on the scale of months or years. Second, natural selection generally increases the evolutionary fitness of individuals, favoring those whose traits allow them to survive and produce more healthy offspring; however, selection at lower levels may increase the fitness of cellular lineages at the cost of the individual. In the case of cancer, this is especially obvious: cancerous cells have an advantage in comparison to other cells in the body, but are disadvantageous to the organism. Selection at the cellular level may wind up hampering the organism's survival and reproduction, acting in exact opposition to selection at the individual level.

 

Why has counteracting these negative effects at the level of the individual (i.e., finding a cure) been so difficult? An evolutionary perspective reveals the answer: cancer — even within one person — isn't a single entity. It's a diverse and evolving population of cell lineages. A single tumor, for example, is made up of a variety of cell types, produced as the cells proliferated and incurred different mutations. All of this diversity means that the population of cells could easily include a mutant variety that happens to be resistant to any individual chemotherapy drug we might administer. To make matters even more difficult, treating the patient with that drug creates an environment in which the few resistant cancer cells have a strong selective advantage in comparison to other cells. Over time, those resistant cells will increase in frequency and continue to evolve. It's not surprising then that a simple cure for cancer has yet to be developed: treating even a single type of cancer is a bit like trying to take aim at a whole set of moving targets all at once.

 

Another perspective on cancer: Evolution within

 

Neoplasms are microcosms of evolution. Within a neoplasm, a mosaic of mutant cells compete for space and resources, evade predation by the immune system and can even cooperate to disperse and colonize new organs. The evolution of neoplastic cells explains both why we get cancer and why it has been so difficult to cure. The tools of evolutionary biology and ecology are providing new insights into neoplastic progression and the clinical control of cancer.

 

Cancer as an evolutionary and ecological process : Abstract : Nature Reviews Cancer

 

HHMI's BioInteractive -The Evolution of Cancer

 

"A tumor cell population is constantly evolving through natural selection," says Carlo C. Maley, Ph.D., an assistant professor in the Molecular and Cellular Oncogenesis Program at Wistar whose own research focuses on this area. He is senior author on the new review. "The mutations that benefit the survival and reproduction of cells in a tumor are the things that drive it towards malignancy.

 

Maley notes that there are three necessary and sufficient conditions for natural selection to occur and that all are met in a population of tumor cells. The first requirement is that there be variation in the population. This variation is evident in tumors, which are a mosaic of many different genetic mutants.

 

The second condition is that the variation must be heritable. This, too, can be seen within a tumor-cell population. When mutant tumor cells divide to replicate, the daughter cells share the same mutations.

 

The final condition is that the variation has to affect fitness, the survival and reproduction of the cells. All of the characteristics that are considered hallmarks of cancer affect fitness, according to Maley. Among these are that cancer cells no longer heed normal growth inhibition signals in their environment, they no longer require an external signal to divide as healthy cells do, and they are able to suppress a vital set of internal instructions that require cells to self-destruct when their genes are mutated beyond repair. This protective cell-suicide program carried by normal cells is known as apoptosis.

 

Does Natural Selection Drive The Evolution Of Cancer?

 

Pyrotex, aren't your three conditions fulfilled above?

 

CraigD's other mention about species, etc. relies on a term that is especially hotly debated or even doubted in the world of microbiology. There are many working definitions of what is or isn't a species. The concept of a "species" works fine for most of the life sciences until you get to microbiology. Different biologists have different species concepts. And that's another can of worms I don't feel like opening up.

 

Species problem - Wikipedia, the free encyclopedia

[Kayra]

Well drat.

So much for my "Origional" idea :0

 

Thanks for the amazing amount of information Maikeru.

[Pyrotex]

Meikeru,

well, even if I give you the benefit of the doubt, every "species" of cancer goes extinct when its host dies or the cancer is destroyed medically.

 

It's kind of like saying, if we expand the definition of a "rock" to include planets and stars, then wouldn't a chunk of coal be like a black hole?

 

Well... maybe... I dunno... sorta... I guess... but what's the point...?

[Moontanman]

Meikeru,

well, even if I give you the benefit of the doubt, every "species" of cancer goes extinct when its host dies or the cancer is destroyed medically.

 

It's kind of like saying, if we expand the definition of a "rock" to include planets and stars, then wouldn't a chunk of coal be like a black hole?

 

Well... maybe... I dunno... sorta... I guess... but what's the point...?

 

I dunno Pyro, I think maikeru has you on this one, the cancer looks to me more like an ecosystem exploiting resources. Much like life on the Earth, because the Earth will eventually die, if you look at the earth as the host of life, then does that mean life on the earth does not evolve?

 

I don't see how you can say the time limit means no Darwinian Evolution goes on.

 

An asteroid sized chunk of coal, say 100 miles in diameter would be quite bright in the night sky if it were close enough or through a telescope so I don't understand the comparison of a chunk of coal and a black hole.

[Pyrotex]

... so I don't understand the comparison of a chunk of coal and a black hole.

Exactly my point. :shrug:

[Kayra]

Heya Pyrotex

 

What is the relevance of the host (and consequently the community of cancer cells) dying have to do with that cancer community showing all the signs of evolution?

 

Extinctions occur constantly. Communities constantly died out because they ravage the environment that spawned them. Does that mean an evolutionary proccess did not occur while they existed?

 

<rewritten for clarity>

[Pyrotex]

Heya Pyrotex...

Extinctions occur constantly. Communities constantly died out because they ravage the environment that spawned them. Does that mean an evolutionary process did not occur while they existed?...

Well, no. It does not mean that an evolutionary process did not occur.

You're right.

 

Hmmm...

[maikeru]

Meikeru,

well, even if I give you the benefit of the doubt, every "species" of cancer goes extinct when its host dies or the cancer is destroyed medically.

 

Evolution does not require that every population or all populations survive indefinitely. Remember we discussed individuals (especially in the context of cells as individuals), populations (of cells), heritability (from cell to cell), etc. Evolution has little to do with immortality.

 

It's kind of like saying, if we expand the definition of a "rock" to include planets and stars, then wouldn't a chunk of coal be like a black hole?

 

Well... maybe... I dunno... sorta... I guess... but what's the point...?

 

Depending which lens you look through, what you see is a world unto itself. IMO, it is not a matter of "expanding" a definition so much as realizing that the definition cannot be truly universal and universally applicable to all instances or particulars that might fall under its jurisdiction. Then you realize the problem is not the particulars that fall outside or do not fit neatly within the boundaries, but the definition itself because it fails to accurately describe the totality of what it supposes it. Or more simply, the definition is lacking and inadequate, more or less so depending on what it is applied to. Mostly there, but not all there. That's why biologists maintain many kinds of working definitions for what is and isn't a species. It's a useful construct to understand what's going on, as best as we can understand by simplifying, classifying, and conceptualizing. It's more difficult--maybe too difficult--for us to understand it in its unvarnished and simplistic totality. As long as we accept that and realize that it can be a strength as well as a weakness sometimes, I think we're good.