The relatively new discipline of evolutionary medicine is making strides in the fields of cancer treatment and antibacterial resistance.
At age 20, Randolph Nesse was puzzled about why we grow old. He couldn’t wrap his head around why natural selection had not eliminated ageing altogether. He spent months coming up with theories to explain it, but was unable to solve the riddle. Yet, this idling of his inquiring mind would lay the seeds for a whole new way of thinking about medicine.
Some years later, friends at a local natural history museum pointed Nesse towards the theory that ageing is simply a side effect of the evolutionary pressure that has selected certain genes over others. If a condition only manifests after an organism passes its reproductive peak, then there will be no selective pressure to prevent it from being passed on. As a physician, Nesse realised that while he understood how these forces could shape species, he had no clue how natural selection works inside the human body.
“I learned one half of biology. Nobody had ever talked about the relevance of evolutionary biology [in medicine],” says Nesse. “I immediately started wondering if there were similar explanations for genes that cause disease.”
Nesse is now credited as a founding father of evolutionary medicine, sometimes also known as Darwinian medicine – a relatively new and growing discipline that applies evolutionary theory to questions about human health and disease. While most modern medical research focuses on the physical and molecular causes of disease, evolutionary medicine tries to understand why we might have evolved to be susceptible to conditions in the first place, and how we can use evolution to fight them.
“What we’re dealing with here is a whole new basic science that has not been applied to medicine,” Nesse says. It’s a very large enterprise to completely upend what we think about what the human body is and how it works. Yet, a growing number of scientists are trying to apply evolutionary thinking to improve medicine. Their work is already starting to change our understanding of how cancers and autoimmune diseases develop. It is also revealing new strategies for tackling pernicious healthcare-related problems such as antimicrobial resistance.
“I’ve been amazed that there have been so many practical implications so quickly,” says Nesse.
Cancers are themselves a demonstration of the evolutionary process in a microcosm. They are clusters of cells that are continually competing and cooperating with each other in ways that help the tumour grow and flourish. One recent study highlighted the almost “infinite” ability of cancer cells to evolve and survive. When a patient receives drug therapy, for example, it introduces a new selective pressure that weeds out the cells that are most vulnerable to the treatment. Those that are less vulnerable, or even immune from the effects of the treatment, survive to pass on their genetic traits to the cells that follow them. It is why even highly successful cancer therapies will eventually stop working in many patients – the cancer cells develop resistance to the treatment and then uncontrollably grow their populations.
“It is arguable that this is the proximate cause of death in most patients,” says Robert Gatenby, the co-director of the Center of Excellence for Evolutionary Therapy at Moffitt Cancer Center, in Florida, US. Through the lens of evolutionary thinking, Gatenby’s laboratory is developing two different strategies to tackle cancer: adaptive therapy, and extinction therapy.
Source: BBC News