I know what Cancer IS – but i never heard WHY it is . . . is it just mutations gone wrong? Seems strange that evolution would leave such a weakness – (or since it usually strikes later in life maybe that doesn’t hurt reproductivity)
So why?
From what I gather cancers are the result of natural cell division having been perverted through exposure to carcinogens, so that the newly produced cells are now pathological. A bit like the way eczema is an excessive proliferation of skin cell growth.
Also the fact that most cancers are contracted after child-bearing age means that evolution wouldn’t have an impact on it.
(IANAParticularlyCleverPerson)
It doesn’t even have to be caused by exposure to carcinogens/mutagens.
DNA molecules are very long, very complicated. The process for cell reproduction is, very very basically:
- copy DNA,
- organize the two DNA bundles separatedly,
- the “skin” of the cell goes from being a 0 to an 8 to being two os, at which point you have two cells, tada!
If there is a point in the copying where a reaction step goes slightly wrong, a mutation is produced, an inexact copy. Mutagens are substances that increase the risk of errors.
The organs where cancers start are organs where cells reproduce a lot. As there is a lot of copying going on, there is also a higher probability of mistakes than where you have less or no reproduction.
If a mutation happens in the reproductive organs, a child can get it (the parent won’t have it in the rest of his/her cells); the child will have the new gene in all his/her cells and be able to transmit it to half his/her descendants. If the mutation is beneficial, the child’s descendants will be able to reproduce more often than those of others, and transmit the not-so-new-anymore gene. That’s what we call evolution.
When a mutation leads to a cell that keeps splitting itself (faster than its nonmutated sisters), that’s a tumor. Depending on rate of growth and on how it affects the rest of the body, it’s a “malignant tumor:” cancer.
Having the possibility of mutations isn’t “bad” per se. The problem is that some of those mutations are bad. So, yeah, cancer is mutations gone bad.
In a healthy human body, the rate by which cells multiply is determined by complex regulatory interactions between the cells. Hormonal signals, cell-cell interactions and interactions between cells and the intercellular matrix all influence whether a cell dies, survives, differentiates or propagates. Some types of normal cells have to grow very rapidly, e.g., the cells lining the gut all gets completely replaced about once a week, while
other cells, e.g. neurons, do not replicate any more in the adult.
In cancer cells, this regulatory network is broken in such a way that in the cancer cells the signal transduction pathways that tell a cell to divide is constitutively turned on, and signals that tell the cell to stop dividing or even to undergo programmed cell death (apoptosis) are ignored.
This cell growth control system has to work properly from conception to adulthood- Cells have to be able to grow quickly as the fertilized egg cell grow fast during fetal development and childhood, slow down as the organism reaches its adult size and speed up again for wound healing after injury.
Many of the regulatory systems involved actually have been more or less optimized for best overall survival: For example, a key gene regulatory protein in cancer called p53 appears to be involved both in cancer prevention and in aging. Mice that have been given an extra copy of this gene were shown to be more resistant to cancer, but to age faster, while mice producing less of this protein did age more slowly but were more prone to cancer (cite) .
An other example is the immune system: Our immune system probably gets rid of most developing cancer cells long before a detectable tumor forms. Patients with an impaired immune system, whether due to an inborn genetic defect, due to immunosupressive therapy after an organ transplant or due to HIV infection have a higher risk of developping cancer. We only see those instances of malignant transformations of cells where the immune system failed to recognize the problem. A more active immune system might be able to eliminate a larger proportion of these, however, it would at the same time carry a higher risk of autoimmune disease.
For anyone interested in reading about the origin of cancer, I highly recommend “One Renegade Cell” by Robert Weinberg. It’s a very good (non-technical) introduction…
Evolutionary processes are at work ‘for’ the cancer and ‘for’ the human.
Not that evolution is ‘trying’ to do anything.
Think about the flu. It mutates regularly. As a consequence, the human immune system is caught off guard. Flu virus survives, but so does its host group.
‘Why’ human cancer exists? Well, because it obviously doesn’t stop the human population from spreading/expanding/reproducing.
Evolution is an explanation, not a mechanism that is out to accomplish anything. If a thousand species go extinct this year, that doesn’t mean evolution ‘failed’. Its just natural selection.
Philster hit the point, but evolution does have one goal, it sets out to produce life that can live long enought to replicate itself
For an interesting example of what can happen when the normal regulatory mechanisms of a cell are not functioning properly, look up Henrietta Lacks and the immortal HeLa cell line that was produced by the cancer that killed her.
According to this guy, cancer is only a fungus, and can be treated with sodium bicarbonate.
:rolleyes:
It was hinted at up thread but I read the same thing recently and that it was interesting. Everyone gets cancer and pretty often too. Thankfully, our immune system is able to beat it back before it becomes anything dangerous most of the time.