Fifteen Eighty Four

Academic perspectives from Cambridge University Press


Darwin and the “web of complex relations”

Devin Griffiths

Darwin was sick most of the time. He spent his adult life trying to recover from the physical toll taken by his famous Beagle voyage. But he was also fascinated by disease, especially diseases, like rabies, that could infect animals as well as humans. For Darwin, the movement of disease between species suggested the common nature of all life, providing evidence for our deep evolutionary history, and the intimate relation between humans and the other creatures – animals as well as plants – that make up our world.

Pasteur’s research into the rabies virus produced the first attenuated vaccine in the 1880s, a breakthrough that lead many to imagine medical science would one day eliminate infectious disease. And ever since – as work by scholars like Lorenzo Servitje reveals – epidemiologists, health organizations, and governments have talked of a great war to defeat illness, with endless pitched battles against a series of threats (whether polio, or flu, or malaria), and as an arms race, in which we seek better drugs, vaccines, and antibiotics to defeat these diseases once and for all.

You might say there’s something Darwinian in this thinking, imagining humans pitted in a war of survival against the microbiota that seek to take our lives. But this misunderstands both the nature of the problem we confront today and the texture of Darwin’s thought. Even if Darwin is best known for natural selection, popularly conceived as the survival of the fittest, his more basic insight was that natural systems evolved to become increasingly dependent on each other. In a passage from the Origin of Species, he muses on the interdepedence of clover, honey bees, mice, and cats: “it is quite credible that the presence of a feline animal in large numbers in a district might determine, through the intervention first of mice and then of bees, the frequency of certain flowers in that district!” This was just one more example, for Darwin, of “how plants and animals, most remote in the scale of nature, are bound together by a web of complex relations.” In the book that immediately followed, Darwin detailed lovingly the intricate adaptations through which orchids adapt to their insect pollinators: luring their interest, rewarding their attention. Until that time, most botanists assumed that bees, moths, and other insects were robbers, thieves who stole nectar from various flowers. Darwin showed that in fact most of these relations were beneficial, helping the insects live, helping the orchids reproduce and sustain their delicate lives. Darwin’s larger question was precisely this: in spite of competition, how does nature hang together? How do creatures become so deeply interdependent? He was, in a word, ecology’s founder.

Recently, a similar shift has taken place among virologists. We used to see viruses simply as diseases, machines that hijack living systems to propagate themselves. In his bestseller, The Hot Zone, Richard Preston describes them as “molecular sharks.” But it turns out that viruses are locked in a close evolutionary embrace with the species they infect, and that in some cases, this embrace may be beneficial. Humans (and in fact, all complex organisms), carry tons of viruses that are seemingly benign. Over time, we evolve with our pathogens, and they seem to evolve with us, settling into easier accommodations (as Luis Villarreal has long noted). Evidence is beginning to emerge that some species, like bats (a former host species of the SARS-COV-2 virus) have evolved to avoid killing off their viruses entirely, developing mechanisms that allow the viruses to persist, but not wreak havoc on their hosts (a point brought up recently by John Yewdell of the NIH). The key question: why? What might viruses be doing for us?

It may take some time to find out (though there is strong evidence that viruses play an important part in species evolution, perhaps even human evolution). The larger point is that viruses are a basic element of the human ecology, and we have to learn how to evolve with them. We are only now getting comfortable with what we’ve learned about the beneficial effects of our personal biome. A reappraisal of our viromes may be just around the corner. Vaccines, antivirals, and other therapies will play an important role in that process, helping us learn how to move into that future without permitting viruses to do so much harm to our lives and to those we love. To do that, perhaps what we need is a more Darwinian frame of mind: one that sees viruses as part of the story of where we come from, where we are going, and our deep dependence on “complex relations” with the world around and within us.

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