Some Assembly Required’ Review: How Nature Finds a Way Did a virus help humans develop the ability to read, write and remember? Animals that fly evolved wings independently, but due to the physics of matter wings always share a similar form. PHOTO: PASCAL GOETGHELUCK/SCIENCE SOURCE By Daniel J. Levitin March 27, 2020 6:08 pm ET SAVE PRINT TEXT 9 If you’re over about 20 and learned about evolution in your high-school biology class, it’s likely that there were a number of things that didn’t seem to add up, and that you were exhorted to just take on faith. Random mutations occur, and across millions of births, the story goes, every once in a while an individual ends up with a mutation that confers a benefit for reproduction, or at least for living long enough to reproduce. The classic example is white-bodied moths (Biston betularia) on the trunk of a tree with white bark—they blend in and so are more difficult for predators to pick off. After the industrial revolution in the U.K. turned many of the white-barked trees black with soot, some moths that had randomly become black were better camouflaged; soon they were the only ones left to reproduce, and all U.K. moths became black-bodied. As science, evolution is not like a chemistry experiment, where you can mix baking soda and vinegar and see an instant reaction, or a physics experiment where you slam one pool ball into another. Like relativity theory, evolution can only really be understood through thought experiments. But those don’t work so well for larger-scale changes. Why don’t we see more “intermediate” species, such as fish with legs or short-necked giraffes? How could anything as complicated as eyes have developed through evolution? They are an intricate mechanism that requires a lot of different parts working harmoniously together, and in isolation the development of only a few of these parts would be pointless. Many a high-school and college student is left to throw questions like this onto the pile with other unanswerables, such as what there was before the universe formed, or whether cannibals avoid eating clowns because they taste funny. SOME ASSEMBLY REQUIRED By Neil Shubin Pantheon, 267 pages, $26.95 In “Some Assembly Required,” as well as his previous popular-science masterpiece “Your Inner Fish,” the biologist Neil Shubin shows himself to be a natural storyteller and a gifted scientific communicator. This new work catches us up on the latest progress in understanding such complicated cases—and there has been a lot of it, some providing the kind of hard, tangible evidence that many scientists once thought would be impossible to find without a time machine. But a time machine is effectively what Mr. Shubin and his colleagues at the University of Chicago and elsewhere have found by studying fossils, and by studying the natural variation that occurs in contemporary species such as salamanders. The author points out the very logical notion that not every mutation is equally as likely to occur. There are constraints—in the structure and materials of bones, cartilage and joints, for example. Consider flight—many creatures fly, but the feat takes similar form across bats, “flying” squirrels, birds and insects because flight requires a great surface area in order to bring the organism aloft. Yet wings are made out of a variety of things—webbing between fingers and toes, feathers and the translucent polysaccharide of insect wings. Animals that fly arrive at wings independently, but once they do, the physics of the matter dictates that wings will share a similar form. What about that missing link, the short-necked giraffe? Mr. Shubin describes something even more spectacular: independent evolution of radically different forms of an organism that have been geographically separated. Various Caribbean islands have similar lizards on them. Forest lizards come in three types, with specialized adaptations for living in the canopy of a tree, on the trunk or near the ground. You might expect that the canopy-living lizards, with their big, deep green heads (the color of foliage), would be most closely related to other canopy-living lizards across the islands. But they’re not. Rather, the lizards on each island “are most closely related to others on their own island.” What began as a single type of lizard on a given island became, over time, three types—on each island, they adapted independently, with evolution producing the same result over and over again. Something similar took place with mammals. Marsupials—those pouch mammals that include the kangaroo, wallaby, koala and, here, the Virginia opossum—include diverse species that mimic the forms of nonmarsupial mammals, another instance of evolution independently coming up with the same result. “There is a marsupial flying squirrel, a marsupial mole, a marsupial ground cat and even a marsupial groundhog. And those are just the ones that are alive today—marsupial lions, wolves, and even saber-toothed cats” once roamed Australia. These findings show us that the diversity of life as we know it is not the one-in-a-million shot of contingencies being just so. The forms that organisms take are constrained by the ways “genes and development build bodies, by the physical constraints of environments.” There is a certain poetry to Mr. Shubin’s account, as when he explains that “the genetic architecture that builds the bodies of flies, mice, and people reveals that we are all variations on a theme. From a common toolkit come the many branches of the tree of life.” You might say it’s in-gene-ious. With so much in the news about coronavirus, we could all do with a better understanding of what viruses are and how they work. Mr. Shubin provides: “Viruses . . . have genomes stripped of everything but the machinery needed for infection and reproduction. They invade cells, enter the nucleus, and invade the genome itself. Once in the DNA, they take over and use the host’s genome to make copies of themselves . . . with this infection, a single host cell becomes a factory to make millions of viruses.” Viruses are not “designed” to be destructive; indeed, if they are too infectious, the host will die and so will the viruses. And of course, not all viruses are bad; some are beneficial. So here’s where the story gets really wild. Scientists discovered a gene called Arc (Activity-regulated cytoskeleton-associated protein) that is activated every time you learn something; flaws in this gene have since been implicated in amnesia and Alzheimer’s disease. All land-living animals have the Arc gene, due to a virus (a relative of HIV, by the way) that invaded the genome of our common ancestor, about 375 million years ago. Once the virus entered a host, it brought with it the ability to make a protein that enhanced neuroplasticity and memories. Traits can appear in one species, only to be borrowed, stolen and modified by another through viral infections. “Our ability to read, write, and remember the moments of our lives,” Mr. Shubin writes, “is due to an ancient viral infection that happened when fish took their first steps on land.” Viral infection, and later domestication of the virus, is now understood to be a source of these “independent inventions,” such as the weird coincidence that written language appeared more or less simultaneously all around the globe. If you’re reading this while sheltering in place during the coronavirus pandemic, thank a different, benevolent virus for giving you the ability to read. And to remember that favorite song you want to play next time you’re feeling down. —Mr. Levitin’s latest book is “Successful Aging: A Neuroscientist Explores the Power and Potential of Our Lives.”
