Darwin's Theory and Cancer
Darwinist blogger Orac recently took issue with my observation that Darwin's theory plays no important role in medicine. Orac, a surgical oncologist, insisted that Darwin's theory is very helpful in modern cancer research. He wrote:
Now, using the principles of evolution, Maley et al have found one potential indicator of which patients with Barrett's esophagus will progress to cancer and which will not. Basically, they adapted a diversity measure from ecology and evolution known as the Shannon diversity index. I'm going to have to leave it to my evolutionary biology colleagues to tell me more whether this was appropriately done, but for purposes of this paper the authors treated each sample ot as a single organism but as thousands of cells. Diversity was measured as the number of distinct clones of cells within the specimen. Using various measures of genetic diversity, including loss of heterozygosity (LOH), microsatellite instability, and differences in chromatin content and telomere length, the number of distinct clones in each patient was estimated and the Shannon index calculated. These were then correlated with the occurrence of cancer. The investigators also controlled for established genetic risk factors, such as loss or mutation of the p53 tumor suppressor gene.Darwin's contribution to the understanding of cancerous transformation in Barrett's esophagus is negligible. Orac asserts that the authors treated each tissue sample not as "a single organism" but as "thousands of cells." That's not new. The view that tumors are heterogeneous aggregates of "thousands of cells" dates to Virchow, in the mid-19th century. All pathologists think of tumors (and pre-cancerous tissue) as thousands of cells, and no oncologist treats tumors as "a single organism." Chemotherapy and radiation therapy are designed with the view that the tumor is a heterogeneous collection of cells. That's why radiation therapy is usually delivered in fractionated doses over a period of time, to destroy cells that are cycling through intervals of sensitivity and insensitivity. Is the view that pre-cancerous lesions are "thousands of cells" and not just a "single organism" really novel to Orac, who is a surgical oncologist? Of course not.
We have known since the 19th century that abnormal "diversity" of cells makes cancerous transformation more likely. This is the traditional basis for the microscopic classification of tumors as benign or malignant. Maley, et al have applied Shannon's diversity index to counting genetic clones of cells in pre-cancerous lesions. The more genetic diversity, the more likely the lesion is to become cancerous. Their statistical method may provide more reliable predictions than the traditional less-quantitative methods, but the basic concepts are very old, and they gain little from Darwin's theory.
Yet Darwin's theory is related to cancer, in a very important way. Darwin asserted that all natural integrated biological complexity arose by random variation and natural selection. Cancer does seem to grow in accordance with Darwin's mechanism. The "variation" of cancer cells seems random, and cancer cells are certainly "naturally selected," in the tautological sense that replicating cells eventually outnumber non-replicating cells. Darwin's theory can be applied to cancer, trivially.
The converse is more interesting: cancer can be applied to Darwin's theory. Cancer is a Darwinian process, unlike the examples of experimental molecular design and artificial selection that Darwinists often cite inappropriately as applications of Darwin's theory. Darwinists claim that "random variation and natural selection" is a model of cancer growth, and they're right.
However, Darwinists also claim the antithesis. Darwinists claim that all functional biological complexity--the seamless integration of cells, tissues, organs, and systems--arose by random mutation and natural selection. Yet cancer demonstrates the destructive power of random mutation and natural selection. Cancer cells don't make better organs and they don't create new integrated physiological systems.
The evolutionary biology literature is generally tangential to Darwin's central claim that all natural biological complexity arose by chance and necessity. It is the cancer literature that actually addresses Darwin's mechanism--random variation and natural selection--as applied to functional biological complexity. It is a model of biological disintegration.
Cancer is the clearest empirical test of Darwin's theory. Tumors, without exception, degrade biological function and integration. Darwin's mechanism of "random mutation and natural selection" never gives rise to life. It destroys it.