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Darwinian Medicine and Proximate and Evolutionary Explanations

This post is a continuation of my reply to Jerry Coyne's post on Darwinian medicine.

Evolutionary biologist Ernst Mayr asserted that there are two ways to understand biology: proximate explanations and evolutionary explanations.

Proximate explanations are the description of the process itself. A proximate explanation of type 1 diabetes is that it is caused by lack of insulin. A proximate explanation of Duchenne muscular dystrophy is that it is a recessive X-linked genetic disease that causes muscle degeneration, weakness and death. Males are affected, though females can be carriers. It is caused by a mutation in the dystrophin gene on the X chromosome (Xp21).

As you can see, proximate explanations are what medical researchers would call the scientific explanation for a disease. Proximate explanations are medical science and provide the foundation for all medical treatments.

Evolutionary explanations are speculation about how a disease came to be. For example, the malaria parasite (eukaryotic protists of the genus Plasmodium) insinuates itself in the hemoglobin of red blood cells. The abnormal hemoglobin of people with sickle cell trait is less hospitable to the malaria parasite, thereby giving people with the genetic trait some protection from malaria. Homozygous sickle anemia is often fatal, but the carrier state may confer benefits in an area in which malaria is endemic. This implies that it is possible that sickle cell anemia is an evolutionary adaptation to malaria.

The theory about sickle cell anemia and malaria is perhaps the most established application of evolutionary reasoning to disease. Other speculations, such as the speculation that malaria makes people prostrate so that mosquitoes can more easily land on their skin and transmit the disease to others, is a less accepted theory.

The difficulty with evolutionary explanations in medicine is:

1) All of the relevant pathophysiology is provided by the proximate explanations, which are the only explanations useful for treatment.

2) Evolutionary explanations are based on proximate explanations -- scientists understand a disease, and then, based on the detailed proximate explanation for the disease, evolutionary biologists concoct speculations as to how the disease evolved. Evolutionary explanations are always dependent on proximate explanations, not the other way around.

3) Evolutionary explanations do not provide a substantial basis for therapy. Even in situations in which evolutionary biologists claim that an evolutionary explanation has provided therapeutic insight, actual scientific confirmation of the effect of the therapy (i.e.- the proximate explanation) is needed to actually implement the theory.

4) Evolutionary explanations by themselves are worthless to medicine. All medical treatments are based on detailed proximate explanations

5) Even in areas of medicine in which evolutionary insight is claimed to be important (such as the development of antibiotic resistance in bacteria), the necessary expertise -- microbiology, cell biology, molecular biology, molecular genetics, population biology, pharmacology, pathology, etc. -- is already an integral part of medical education and research. Evolutionary biology has contributed nothing of substance in the past, except to point out that bacteria that are not killed by antibiotics are not killed by antibiotics, which is sole insight provided by 'natural selection' to antibiotic resistance.

6) As evolutionary biologists readily acknowledge, there are very few evolutionary biologists in medical schools, and modern medicine has progressed rapidly and far without evolutionary speculations about disease.

7) Evolutionary speculations about disease belong in departments of evolutionary biology, not in medical schools. Any genuine insight provided by such evolutionary speculation can be communicated to medical researchers through the normal process of communication (a brief e-mail, a paper presented at a scientific meeting, etc)

8) The incorporation of evolutionary biology in medical school curricula is a waste of valuable resources. It is the actual proximate scientific explanations for disease that guides medical research. Speculation about biological origins already has a scientific home, and provides little help to medicine.

More to come.

Cross-posted on Egnorance