Cancer a method for early Earth Evolution?

Question

Something I have been wondering for a while is looking at cancer from an evolutionary standpoint.

It's easy to conclude (from observations today) that cancer is something we would rather avoid. However I kept asking myself what would be the purpose of cancer existing in the first place? In my experience of studying biology if a organism or mechanism in nature exists it is because there was a pressure to create it.

It has led me to think that perhaps early on, when cells were just beginning to clump together forming very very primitive organisms, that cancer was a way for a cell to proliferate very quickly and make their particular genomic sequence more common within what would have been organisms made of a lump of cells. Perhaps the different organs we have today exist not just because there was environmental pressure to have a specific organ with a specific function. Perhaps the cells descended from a "cancer" that proliferated faster over other cells in a primitive ancestor of that organism.

The answer that "cancer exists because our bodies make mistakes" doesn't satisfy me when everything else around us evolved and formed due to a multitude of different pressures.

In an effort to make this question less broad my question is basically this:

Is it plausible that cancer is a phenomenon that began to occur relatively early in Earth's evolutionary history as a form of survival for cells in primitive organisms or am I applying evolutionary theory incorrectly?

(I know there is a better word for "pressure" to describe the variables that guide evolution but right now my brain can't come up with anything better).

Answer 1

There is a lot of terminology, semantic and biology to be discussed if one was to fully answer your question and it would take a whole book. Below I am just trying to push you to reading more on the subject.

Evolution of cancer prevalence

The probability of getting a cancer is under selective pressure for sure. Citing cancer.net, here is some information on the genetics of cancer:

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Many of the genes that contribute to the development of cancer fall into broad categories:

• Tumor suppressor genes are protective genes. Normally, they limit cell growth by monitoring how quickly cells divide into new cells, repairing mismatched DNA, and controlling when a cell dies. When a tumor suppressor gene is mutated, cells grow uncontrollably and may eventually form a mass called a tumor. BRCA1, BRCA2, and p53 are examples of tumor suppressor genes. Germline mutations in BRCA1 or BRCA2 genes increase a woman’s risk of developing hereditary breast or ovarian cancers. The most commonly mutated gene in people who have cancer is p53. In fact, more than 50% of all cancers involve a missing or damaged p53 gene. Most p53 gene mutations are acquired mutations. Germline p53 mutations are rare.
• Oncogenes turn a healthy cell into a cancerous cell. Mutations in these genes are not inherited. Two common oncogenes are:
  • HER2, which is a specialized protein that controls cancer growth and spread, and it is found on some cancer cells, such as breast and ovarian cancer cells
  • The ras family of genes, which make proteins involved in cell communication pathways, cell growth, and cell death.
• DNA repair genes fix mistakes made when DNA is copied. But if a person has an error in a DNA repair gene, these mistakes are not corrected. And then they become mutations, which may eventually lead to cancer. This is especially true if the mutation occurs in a tumor suppressor gene or oncogene. Mutations in DNA repair genes can be inherited, such as with Lynch syndrome, or acquired.

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Somatic Evolution in cancer

A cancer is a group of cells that proliferate. In other words a cancer is a group of cells having a higher fitness than other cells.

See Wikipedia > Somatic Evolution in cancer

Can a cancer be beneficial?

I am here attempting to answer your specific question.

We define a cancer based on the fact that it is detrimental to the organism carrying it. If a group of cells divide a lot more than the others and this is beneficial to the organism, then it is not a cancer but an adaptive developmental process.

Let's generalize the definition of cancer

To generalize the definition of cancer, one can say that a cancer is a group of individuals that proliferate to the detriment of the group. In other words, we need a social group of individuals (such as a multicellular organism) to get a cancer. Depending on your definition of a social group, one could consider a criminal organization as a cancer to human society.

If you push the definition a little further by either leaving out the need of a close phylogenetic relatedness between individuals of the group, one could say that "humans are a cancer of the earth". If you google this sentence you will get many hits!

Answer 2

That is a very insightful question. In general terms, you're right that cancer is unregulated cell division, which hijacks the mechanism of cell division which is ancestral to all multicellular life. In early multicellular life, it may well be the case that faster reproduction was selected for, while it has been selected against for most organisms as they became more complex.

The mutations which cause tumors are usually two-fold: first there is a mutation which causes a cell to get genetically switched on. This might be a mutation causing an overproduction of a protein signalling molecule which tells the cell it is time to grow. The second is usually a mutation in cancer prevention genes, since a cell going haywire is likely to be spotted and destroyed relatively quickly. If both of these mutations happen in the same cell, the cell can form a tumor (and if the tumor spreads to other parts of the body, it is called cancer).

Some people have suggested that cancer be thought of as "cell-level selection." This idea of levels of selection takes a little explanation. When evolution was first proposed (and the way in which it is introduced still) is individual-level selection. Individuals compete against other individuals to survive and reproduce. However George C. Williams suggested (and Dawkins later popularized in "The Selfish Gene") that genes might compete against other genes. This is called the gene-level view. In the mid 1980s, Leo Buss suggested that a cell might also be a level of selection, and that cancer represented cells trying to reproduce at the expense of the individual which carried them.

In some cases, such as instances of transmissible tumors (there are only a few such tumors known in the wild, none in humans). These cancers spread from individual to individual, rather than just within one individual. In that way, the cancer's evolutionary strategy was successful. However these are rare, so if we view cancer as an evolutionary strategy, it is not usually a successful one. As such, thinking of cancer as a cell-level selection has not yielded many interesting ideas so it is not widely used in biology today. It is not incorrect, but it doesn't further many research projects so it is not commonly taught or studied.

There's one exception to that, however. Thinking of cancer itself as an evolutionary process, where cells survive and die off according to their mutations, is very useful to understanding the progression of a tumor. If you're interested in this line of thought, there's a summary paper Merlo et al 2006 which you might want to take a look at.

Answer 3

You are wrong and right. Remi.b's answer is describing the idea is not right and the answer is generally accepted.

The cells in muticellular organisms have to be regulated tightly--some has to differentiate into skin to protect bodies, other, into stomach to secrete digestive enzymes, etc. This regulation was established when multicellular organisms appear.

In other words, unicellular organisms do not care about the regulation. They do not have to be skin, stopping cell growth. Not much problem that they grow as cancer cells do, although you don't call such unicellular cells "cancer" probably because they are not abnormal.