I Am a Rat and So Are You 

by Rob Dunn (SEED Magazine 2009)

HUMANS AND THE DOMESTICATED LAB RAT SHARE DNA, A HISTORY, AND INCREASINGLY, THEIR FATES

Natural selection is stingy in its edits. It takes only three letters to go from “Hamlet” to “ham” and hardly more differences in DNA nucleotides to span the distance back between rodent and Rodin. The entire diversity of mammals reflects a modest tinkering with the original mammal plan. We share 99 percent of our genes with chimps, but we also share 95 percent of our genes with pigs and rats. And so most of the story of humans, our biology and deep history, is told equally well by the body of any mammal — even a lowly rat. Especially a rat.

We imagine the rat as despicable, disease ridden, grotesque. In tandem with fleas and plague, rats nearly did us in. But they may also have saved us. It is from the rat that we have learned most of what we know about ourselves. Look into a lab rat’s black eyes and you will find, if not your sister, an increasingly good mirror. Rats have immune systems like our immune systems. They have brains like our brains, fat like our fat. They have no language. They don’t dream about the stars. But otherwise we are the same. And so we poke them to learn about ourselves. We have long known that rats are like us. What is new is the realization that our similarities to each other are greater each year. More and more, I am a laboratory rat, and so are you.

Our stories and the stories of rats were long divergent. Our most common shared ancestor lived more than 70 million years ago. From there, the lineage that would become the Norway rat — the species that is used in labs and that is also most common in cities — and the one that would become humans went different ways. You know our story. As for the Norway rats, they evolved somewhere in Asia in ancient history (“Norway” having apparently been bestowed on the rat by the Swedish). Eventually, they found us, our scraps, and our throwaways. They came to our doorsteps and stayed and prospered. As we spread, they spread, from Asia to Europe, from Europe to Americas and then beyond. They spread like and with us (the best evidence of the routes that Pacific islanders took from island to island comes from what we know about the genetics of rats introduced with those humans). As they spread, they carried disease. They also ousted other species and races and came to be generalists, living off what could be had. On islands, they ate flightless birds. In cities, they ate what we left them. They found the scraps of civilization and tended to them with their delicate pink hands.

But times have changed. Few of us still live a self-sufficient life, gathering from the land. We have built cities and industrial agriculture. The wild rat lives a life that echoes our past but is removed from our present. One can still find wild rats (sometimes in great abundance), but most rats escaped that hardscrabble life at the same time we did. They became domesticated. In the midst of the industrial revolution, we brought Norway rats into the lab. We built them apartments, like smaller versions of our own. We fed them, like we fed ourselves, on sugars and without end. We let them grow fat, just as we grew fat. We stripped them of their parasites and doused them with antibiotics, just as we did to ourselves. Wild rats in their varied wild habitats live divergent lives, but lab rats (like, some would argue, humans in cities), have a shared experience of life.

In some ways, the way we care for rats is more advanced, at least technically, than the way we care for our own. In the lab, rat parasites are nearly absent; babies are often born via C-section to prevent transmission of any parasites that might be present. Newborns are moved to sterile environments, by hand, one at a time. Born red-pink with blood and life, they are cared for from that day on. And attempts at even better care continue — all, of course, to the ultimate end of making the rats more useful, though that does not matter to them. While wild rats have become a study in our past, lab rats have become a vision of our future. We test our drugs first on them and then, if they work, use the drugs on them and only later on ourselves. We make discoveries in them and only later prove them to be the case for ourselves. A recent study concluded that rats that are afraid of novelty die sooner. Upon hearing this, one knows the rub: that when we get around to testing it, the same will be true of us. The rats are always a step ahead of us.

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