Cancer does not give us a view of a bygone biological age
Scientific enquiry often benefits from outsiders bringing a fresh insight. The awesome success of molecular biology in the second half of the 20th century, for instance, was driven by a significant number of physicists, attracted by the challenge of understanding the answer to the question, posed by Erwin Schrödinger, “What is life?“.
However, outsiders can also arrive ignorant of important background knowledge and thus make contributions that do not advance understanding because they misunderstand, or omit important aspects of a research topic. Often the proponents of these “new hypotheses” are so enamoured with their idea that they ignore all reasoned objections (and evidence that refutes them). This morning’s Comment is Free section of The Guardian contained a good (or rather bad?) example of this: “Cancer can teach us about our own evolution” by the physicist Paul Davies. He wrote a similar article for The Guardian last year, and I remember a rather confused student citing this after one of my lectures on cell division at the time. The latest article offers no new insight, and crucially no actual evidence.
Davies writes, cancer “is embedded in the basic machinery of life”, a statement that few biologists would take issue with. The problems arise when he explains why he thinks this is the case. His hypothesis, co-proposed with Charles Lineweaver (another physicist), is that cancer cells have somehow reverted back to an ancient state resembling aspects of the single-celled life that existed “on Earth before a billion years ago”. He appears to be arguing that cancer cells are activating a set of genetic pathways that are normally silenced in healthy cells, and that these pathways date back from the time when our ancestors were single-celled. There is a grain of truth in this view, all cells are generated by cell division, and so must contain the machinery and pathways that regulate and activate this process. Since these processes are ancient, actively dividing cells, such as cancer cells, maintain active cell division machinery. However, the same is also true of the stem cells in your bone marrow, which must continually divide throughout your life to maintain the cells that make up your blood, but that doesn’t mean these cells are somehow recapitulating the conditions that existed a billions years past.
Also, although it is true that single-celled organisms, by definition, cannot get cancer, they do not “have one imperative – to go on replicating”. Even single-celled organisms must still coordinate cell division with other cellular processes and signals from outside the cell. For instance, beginning cell division when there are insufficient nutrients, or when the cell is too small leads to catastrophe. Thus, in both single and multi-celled organisms, cell division must be tightly controlled.
The article takes several other liberties with biology, but I don’t have time to take issue with all of them. The estimable PZ Myers has previously upbraided Davies for his use of the long discredited view that human embryos recapitulate key events in vertebrate evolution as they develop: Aaargh! Physicists! This erroneous conception appears again here: “Every human, for example, possesses tails and gills for a time in the womb.” No! Both fish embryos and human embryos have the same general structures that become differentially specialised as they develop. At no point does a human embryo develop gills!
Davies uses this erroneous statement to make the leap that because genes active early in embryonic development are also those “reawakened in cancer” (this is true, for the most part), then this must be because the cancer cells are reverting not only to a state that existed in the early embryo, but to an ancestral, single-celled state. This is a curious logical jump made less for the strength of the evidence and more because it fits the author’s hypothesis.
There is more at stake here than simply getting the biology wrong, or proposing hypotheses that don’t advance our understanding of cancer. Davies is the principal investigator of one of twelve Physical Sciences – Oncology Centres launched by funding from the US National Cancer Institute, at approximately $2,000,000 apiece. To be sure, there may be benefits from this multidisciplinary approach, but only if those involved get the biology right.
Update PZ Myers has just posted an excellent
take down commentary of the Physical Biology paper that yesterday’s Guardian article was based on. Apparently there was also a Torygraph article earlier in the year that I missed, framing this dog’s breakfast of a “hypothesis” as “The final frontier in the war on cancer”!