The modern theory of natural selection derives...
The modern theory of natural selection derives from the work of Charles Darwin in the nineteenth century. (Photo credit: Wikipedia)

If we accept Darwin’s theory of evolution, which I do, then we accept that we are the way we are as a result of a very period of gradual changes brought about by the pressures that our species has experienced through emergence and during process of its existence.

But let’s take a step back. All organisms have so called genetic material, stuff within them which encodes the way they are and the way that their offspring will be. The genetic material is copied as a part of the process of living, of growing and of repairing the organism if it sustains damage.

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If that were all there was to the process, then organisms would be static, with no changes and no evolution. In fact the process is not perfect and both minor and major changes to the genetic material happen all the time, by all sorts of means.

Obviously, if too many changes or major changes occur in the genetic material, then the organism may not grow properly and may not repair itself properly when damaged. Also if the genetic material is passed to the organism’s descendants, they may they may not be viable or they may be disadvantaged and be unable to thrive and reproduce.

Baby turtle, species unknown.
Baby turtle, species unknown. (Photo credit: Wikipedia)

To counter this, our bodies have mechanisms to repair our genetic material, our DNA. If our bodies did not have this ability, it is unlikely that we would last long, as our body cells could experience millions of cases of damage to our genetic material per cell per day. That’s an awful lot of damage!

As described in the Wikipedia reference above, the errors in our genetic material could result in cell death or unregulated growth resulting in tumours. The DNA repair mechanism in our cells  do a good job, but they are only effective if the DNA strands are broken or incomplete. If a change is minor, and is properly reflected on both strands of our double helices, then the repair system will not notice the change.

English: Close up of The Double Helix
English: Close up of The Double Helix (Photo credit: Wikipedia)

This allows small changes to slip through, and provided they don’t cause life threatening problems, they may get passed to our descendants. The same applies to organisms other than ourselves of course.

Some major changes do slip through and organisms may end up with extra chromosomes or with damaged chromosomes. Sometimes these issues may not cause too many problems for the organism, while in other cases the descendant organism may not survive long enough to breed.

English: Illustration of the chromosomal organ...
English: Illustration of the chromosomal organisation of haploid and diploid organisms. (Photo credit: Wikipedia)

The minor errors mentioned above may affect the descendant organism to some extent, making it more or less successful than its parent organisms. The theory of evolution suggests that if the change in the genetic material makes it more successful than its siblings who don’t have the small errors, then, over generations, organisms carrying the new DNA changes will eventually replace those who don’t carry the change.

This could lead to problems for an organism. If we consider a stable population with few pressures, that has plenty of resources, there is little that would cause any permanent changes to the population, and small genetic traits could appear and disappear over time and not have any measurable effect.

Boreray sheep - on Boreray - geograph.org.uk -...
Boreray sheep – on Boreray – geograph.org.uk – 1439988 (Photo credit: Wikipedia)

If the environment then changes, such that one trait provides a large benefit to those individuals who have this trait, then over time there will be a tendency for the trait to be found in more individuals and the number of individuals without it would fall.

If the environment changes back again, then those with the trait may be disadvantaged and those without the trait could then come to dominate the population. However if enough time had passed and all the individuals without the trait in their genetic material had died out, then the population would be stuck with the trait.

Français : Trait du Nord - Salon de l'Agricult...
Français : Trait du Nord – Salon de l’Agriculture 2010 (Photo credit: Wikipedia)

It would be extremely unlikely but not impossible for the change in the genetic material to be reversed by chance as this would require another minor error to exactly reverse the original error. In effect, evolution as reflected in the genetic material never (or astronomically rarely) reverses.

If a group of organisms gets isolated from the rest of its species, some of the genes that are present in the population at large will not be present. In addition, some of the genes in the isolated population will also die out, either by chance, or because the trait that they confer is not beneficial in the isolated environment.

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This can cause problems for the population if the environment changes dramatically to the detriment of the organisms. While the population at large may have genes which would enable the population to survive the changes, but those genes may have died out in the isolated environment, and the population may fail.

Of course, a mutation may arise which would enable organisms to survive in the new conditions, but environmental changes would almost certainly be faster than the rate of evolution through mutation.

exemples de mutations possibles sur l'ADN
exemples de mutations possibles sur l’ADN (Photo credit: Wikipedia)

Some species have different behaviours and appearance while still remaining the same species. Some of Darwin’s finches are an example. At least two varieties of one of the species feed on the Opuntia cactus, but they have different ways of feeding on them. One variety has a long beak and can punch holes in the cacti, while the other variety, with a short beak, break open the cacti to feed.

The birds can and do interbreed, so they are indeed the same species. This is similar, I presume, to the variation in skin colour in humans or the various blood types in humans. Such species have the same genes, but have slightly different versions (alleles) of it. This is called genetic polymorphism.

English: Trumpeter Finches (Bucanetes githagin...
English: Trumpeter Finches (Bucanetes githagineus), Valley of the kings, Egypt. Español: Camachuelos trompeteros (Bucanetes githagineus), Valle de los reyes, Egipto. (Photo credit: Wikipedia)

A species, like the finches, has to adapt. If its environment changes and it is unable to respond, then it will die out as innumerable species have done and are still doing. However, a species needs time to respond to environmental changes. For instance, polar bears may die out because the sea is is not freezing over as it usually does, and as a result there are no seals for the bears to hunt.

Whether or not you attribute the warming to mankind’s actions or not, the lack of freezing is a fact, and the bears are so far unable to adapt to the new conditions, and are often becoming a nuisance to arctic communities.


Why does cancer spread?

The Human Body -- Cancer
The Human Body — Cancer (Photo credit: n0cturbulous)

Everyone, I’m sure, knows of someone who has died of cancer. It’s a disease that is wide-spread and seems to be more common now that other diseases are coming under control. It may be that cancer is certain to appear in the human body if it lives long enough. There’s a cheery thought.

Wikipedia describes cancer as follows: “known medically as a malignant neoplasm, (it) is a broad group of diseases involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumours, and invade nearby parts of the body”.

Cross section of a human liver, taken at autop...
Cross section of a human liver, taken at autopsy examination, showing multiple large pale tumor deposits. The tumor is an adenocarcinoma derived from a primary lesion in the body of the pancreas. (Photo credit: Wikipedia)

There’s two parts of this definition. Firstly there is the unregulated cell growth and secondly there is the spread of the growth to other parts of the body. The unregulated cell growth is usually attributed to a number of causes, but the mechanism is usually given as damage to the genetic material. The causative agent whatever it might be, damages the genetic material and this results in a huge proliferation of cells.

I write computer programs as tools for doing my job. Each program ends up as a string of data which a human has a hard time decoding, though of course the computer hardware has no problems. The effect of changing a single bit (actually, a byte) of a program would almost certainly cause it to crash. In so far as the analogy that the genetic code resembles a computer program holds, this indicates that a random change to the genetic code would most likely result in the death of the cell. It would require a specific hit, to say a piece of code that control the termination of a loop that would let the program “grow out of control”.

Out of memory ATM
Out of memory ATM (Photo credit: RuiPereira)

I’d guess, from a position of almost total ignorance, that changes to the cells in the body occur all the time. Changes happen to the genetic code in a cell, and it almost certainly dies. (A side question is : what exactly happens to a cell when it dies? Presumably some process or other ‘detects’ the death and breaks it up? Or does the first failure cause other processes to fail until the integrity of the cell is lost? Lots of questions). However, unless the failure is dramatic, explosion-like rather than simple deflation, it should not affect its neighbouring cells, should it? So in general the death of a single cell is probably not noticeable.

Going back to the computer program analogy, in a computer there are dozens, if not hundreds of programs running all the time, but the user is not aware of any other than the one he is interacting with. Equating cells with computer programs, it is most likely that a random change would cause a program or a cell to die, with little effect on the computer or body as a whole.

Facit computer memory
Facit computer memory (Photo credit: liftarn)

All the programs running in a computer need ‘memory’ to run in, and there is a limited supply of memory, so (conceptually at least) one program is given the task of managing the memory allocations. Damaging the memory manager program could theoretically lead to it repeatedly allocating memory until there was none free for allocation. The computer would, once again, crash. If a program is damaged in a particular way it could ask repeatedly for memory and again cause itself or other programs. or even the whole computer to crash.

In a living organism there does not seem to be a single equivalent of the ‘memory manager’ or ‘resource manager’. In a living organism everything seems to be done by consensus between cells. (That is both anthropomorphic and probably naive, but it will do, I think).

So, although I’d estimate that the vast majority of changes to the genetic code would result in cell death and nothing else, a very, very small number of changes could result in the cell soaking up as much of the cell-level resources as it can and damaging the cell itself, its neighbouring cells or the whole organism.

Genetic code
Genetic code (Photo credit: Martina Gobec)

That, however, is not cancer. For damage to result in a cancer it has to damage the cell in a particular way. In a computer, cancer would be analogous to a program continually creating copies of itself and using up all the system resources, which would result in the system crashing. Almost all cells have the ability to duplicate themselves, but whether or not they do replicate is, so far as I know, determined by the conditions in the cell itself and conditions in its environment, ie the surrounding cells, possibly signalled by chemicals or chemical gradients.

For a cell to become cancerous, it first of all must be inclined to duplicate itself and it would also have to be able to ignore any signals from its environment. The damage to the genetic structure to achieve this seems to me to be remarkably specific. Its like damaging a computer program in such a way as to destroy a control loop. Possible, but not very likely.

Main sites of metastases for some common cance...
Main sites of metastases for some common cancer types. Primary cancers are denoted by “…cancer” and their main metastasis sites are denoted by “…metastases”. List of included entries and references is found on main image page in Commons: (Photo credit: Wikipedia)

Then there is the issue of metastasis. This is how cancer spreads. It first of all attacks the boundary of the organ it is embedded in, then some cancer cells migrate into other organs. Interestingly, when they start to form a cancerous tumour in the new organ, they are still identifiable as cells from the original organ.

Think for a moment about what that means. A cancer which metastasizes has to have its genetic material damaged in such a way that it can do all of the following :

  • divide in an uncontrolled manner
  • attack the walls of the organ it is contained in
  • migrate to other organs (and it can be very specific about the organs it migrates to)
  • settle there and start to divide again

That’s a remarkably specific set of actions to occur as the result of damage. Damage usually results in less efficient operation, both of computer programs and bodies. Of course the damage doesn’t have to create these action ‘programs’ in the genetic material. They may be already there. All that the damage needs to do is somehow kick off those actions in sequence to cause the cancer to form and metastasize. To a programmer it would look like a small chunk of code to call those routines which I’ve called ‘actions’. The only other time in one’s life that one’s body experiences explosive growth and cell migration is in the womb and as a young child. One can imagine that damage could somehow kick off the genes or part of the genetic code that was used when one was a developing foetus.

foetus (Photo credit: Leo Reynolds)

This is easier to contemplate than damage which somehow creates the whole process from scratch. It does imply that the damaging agent somehow attacks a specific part of the genetic material and replaces it with some very specific other material that has the specific effect of kicking off explosive growth and metastasis.

I’m not geneticist or cancer specialist of course, so my musings above may be way, way off beam. They could be and probably are complete rubbish. I can’t and won’t defend them if anyone were to attack them. My main thesis is that it seems incredibly unlikely that damage to the genetic material could cause the specific effects of cancer, which are uncontrolled growth and metastasis.

Yet cancer happens and happens frequently and in varied ways. There are many sorts of cancer and they appear to be often triggered by specific stimuli. All my arguments above founder on that logical rock.

Shipwreck (Photo credit: Wikipedia)