Darwin and his ideas have had an enormous influence on modern medicine and medical research, writes MUIRIS HOUSTON.
ALTHOUGH Darwin’s work is primarily associated with biology and zoology, he has had an enormous influence on modern medicine.
His discoveries continue to generate insights. While most doctors do not formally study evolutionary biology, its theories offer a way of understanding why the body is vulnerable to disease.
According to Randolph Nesse, professor of psychiatry and psychology at the University of Michigan, “evolutionary biology offers a framework for organising the diverse facts in medicine”. Writing in Darwin’s Gifts, a special Lancet publication to mark the bicentennial of Charles Darwin’s birth, he says, “physicians who can use both the evolutionary and the proximate halves of biology to understand disease will make better decisions”.
A proximate explanation for a disease describes what is wrong with the body’s mechanism. An evolutionary explanation focuses on why we are all the same, but in ways that leave us vulnerable to disease. Take antibiotic resistance as an example of an evolutionary approach. Most antibiotics are derived from bacteria, which have themselves been battling each other for supremacy for generations. The nastiness or virulence of a particular bug is driven by a desire to spread.
An evolutionary view of MRSA suggests the bug has developed to resist previously effective antibiotics while at the same time utilising new methods of spreading.
An apparent “design fault” that makes us vulnerable to disease can be seen in heart failure. As the heart’s pumping action begins to weaken, the reduced cardiac output leads to fluid retention in the feet and in the lungs, which then makes the heart failure worse.
Natural selection seems to have failed in this instance until you realise the system was designed primarily to deal with dehydration, in which fluid retention is vital to survival.
Nesse has an interesting take on depression. In general, he says that feeling hopeless, worthless and lacking motivation is unhelpful. But what if depression was more like chronic pain than cancer, a deregulation of a response that could be useful in some situations? The psychiatrist says research has yet to identify what these situations are, but he claims there is a general consensus that “low mood offers advantages in inauspicious situations in which all efforts are wasted or risky”. An evolutionary interpretation of chronic disease suggests that humans do not evolve fast enough to keep up with changing environments. If we had strong motives to exercise and eat vegetables we might not now be facing the consequences of an obesity epidemic.
Even our defences have been influenced by evolution. Pain, fever, vomiting, inflammation and anxiety serve a purpose, but maybe the threshold for each of these defences has been set too low and they occur more readily than required. On the other hand, if the body did not initiate these responses early, the outcome could be catastrophic.
If medicine has been slow to acknowledge evolutionary principles in the causation of disease, neither was it of much use to Charles Darwin during his life. He dropped out of studying medicine in Edinburgh and went to Cambridge with the intention of becoming a priest. Not long after returning from his epic journey on HMS Beagle, his health failed and he spent much of his time pursuing some bizarre remedies.
When Darwin first published his theories he upset many in the establishment. The Lancet itself said: “this formula of evolution by natural selection . . . is no explanation but merely a form of words”.
But for those of us who believe in the art as much as the science of medicine, his humble approach and acknowledgement of the many gaps in his knowledge confirm the honesty of his approach.
Dr Muiris Houston is medical correspondent of The Irish Times