Even when we know the mechanisms animals use, the precision with which they use them often defies current scientific understanding. For instance, the clocks of many species are far more precise than the biological clocks available to humans. After just twenty-four hours of continual darkness, the human circadian clock is skewed on average sixty minutes from the actual time. For honeybees, this sort of inaccuracy could prove disastrous. Just fifteen minutes off, explains Gould, and a honeybee could have a ten-degree error in orientation, which over shorter distances might result in a couple dozen feet off course. And for long-distance migratory birds like bar-tailed godwits, errors in accuracy are deadly. Every autumn these birds leave their nesting grounds in coastal Alaska and head south to feed in warmer parts. The sensible route is along the continental arc of Asia to the eastern coast of Australia; there are plenty of landmarks and places to rest along the way. Instead, the godwits set out for the vast open water of the Pacific Ocean. For eight days and nights they fly over more than six thousand miles of featureless ocean before arriving in New Zealand. If the birds make a directional error of even a few degrees, they will be hundreds of miles off course, nowhere near their feeding and nesting grounds, and out of fuel.
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Every year, humpback whales undertake migrations exceeding ten thousand miles across open ocean. These forty-ton mammals don’t travel in the general direction of north to south and back again; instead, the whales return to the exact places they were born and fed by their mothers as calves, which requires exceptional navigation.
Recently a consortium of researchers led by Travis Horton at the University of Canterbury revealed just how precise whales have to be by tagging sixteen humpbacks and tracking their movements with satellite telemetry over seven years. What they found was that for most of the journey, the whales maintained a constant course that barely deviated even a single degree. This takes some unpacking to understand. Humans can maintain a constant course, but only if landmarks are available by which to judge our progress and correct our course as we go. Without such course corrections, we start unwittingly walking in circles. At the Max Planck Institute for Biological Cybernetics, for example, researchers Jan Souman and Marc Ernst have found that this predilection for circles became especially strong in blindfolded individuals; with their eyes covered, people quickly started walking in circles measuring sixty-six feet in diameter; this happens even when people thought they were walking in a straight line. Humpbacks follow a direction “as straight as an arrow,” not just in short bursts but across thousands of miles. And they do it despite encountering multiple elements that could complicate their sense of direction. Humpbacks swim through storms, strong sea currents, and highly variable depth conditions; encounter entire underwater mountain ranges; and do so both during the day and night—and their course often varies less than one degree.
Humpbacks must be constantly compensating for these forces using spatial reference frames and orientation cues, but what are they? Perhaps humpbacks, like so many other species, are using a sun compass. Yet the researchers found that even when individual humpbacks began their journeys in different parts of the ocean, where the sun appeared at different altitudes and azimuths, they followed very similar headings. Other whales starting out in the same locations, where the sun appeared in the same place, used very different headings, meaning there had to be another reference they used to know their location. If humpbacks can’t logically depend on the sun alone, what is the other reference? The navigation of so many species prompts this same question. While the sun, stars, moon, landmarks, olfactory cues, memory, and genetics seem to have a place in various species’ strategies, none can fully explain how so many animals possess a powerful ability to orient with such remarkable exactitude. As a result, scientists have increasingly turned their attention to one of the senses at the so-called simplest level of the navigational toolbox to try and explain the most complicated migrations carried out by the likes of humpbacks and godwits: magnetism.
For decades, the idea of animal magnetic navigation was disparaged by the scientific community as pseudoscience. Then in 1958 a young graduate student in Germany was solicited to disprove the idea once and for all. As science historian Lisa Pollack has recounted, Wolfgang Wiltschko was asked to re-create an experiment conducted by a fellow student, who had put birds in a closed room without sunlight or stars but, to his surprise, discovered they could still orient. There were two possible explanations for this behavior: the birds used magnetism, or they used radio signals emitted from stars. Wiltschko thought the star hypothesis was the likely answer. He put European robins in a steel chamber that weakened the earth’s geomagnetic field, and he kept them in it for several days to try and manipulate their internal clock. But when he tested them in an orientation cage, they were still perfectly oriented. If he reversed magnetic north, the birds could sense the change and switched the direction in which they tried to fly. Working with his wife and fellow scientist Roswitha, Wiltschko became convinced that birds used an inclination compass—the angle between the magnetic field and the horizontal plane of the earth—to navigate, and he conducted dozens of experiments with birds to prove it. Meanwhile, other studies emerged showing that sharks, skates, cave salamanders, snails, rays, and even honeybees seemed to possess a magnetic sense. By the early 2000s, scientists had shown that seventeen other species of migratory birds, as well as homing pigeons, used magnetic compasses.
The notion that animals have a bio-compass that can “read” the earth’s geomagnetic field has now emerged as the most promising explanation of animal navigation. In addition to those marathon migratory species, nearly every animal that has been tested thus far demonstrates a capacity to orient to the geomagnetic field. Carp floating in tubs at fish markets in Prague spontaneously align themselves in a north-south axis. So do newts at rest, and dogs when they crouch to relieve themselves. Horses, cattle, and deer orient their bodies north-south while grazing, but not if they are under power lines, which disrupt the magnetic field. Red foxes almost always pounce on mice from the northeast. These organisms must all have some kind of organelle that functions as a magneto-receptor, the same way an ear receives sound and an eye receives space.
As evidence of such a capacity across species grew in the twentieth century, the allure of a universal theory for animal wayfinding based on magnetism increased. Could a biological compass based on magnetism explain the capacity for species like humpback whales to find their way?
Maybe. The only problem is that no one can find it.
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The search for a bio-compass has now spanned nearly half a century, attracting biologists, chemists, and even physicists. But the anatomical structure, mechanism, location, and neural connections of animals’ magneto-receptors remain a mystery. Kenneth Lohmann, an expert in sea turtle navigation, has called the search “maddeningly difficult.” Magnetic fields, Lohmann wrote in Nature, pass freely through biological tissue, which means that the magneto-receptors could be located almost anywhere inside an animal’s body. They may be so tiny as to be submicroscopic and dispersed throughout a body; it’s even possible that magneto-reception could in fact be a chemical response, which means there’s no single organ or structure devoted to it. “We are still crying out for how do they do this,” the geologist Joe Kirschvink told me. “The compass is a needle in the haystack.”
I met Kirschvink at a conference hosted by the Royal Institute of Navigation, which focuses on modern navigation by air, sea, river, and space. Every three years, their conference dedicated to animals brings together the world’s foremost scientists to present their research. The year I attended it was held at Royal Holloway College, an ornate Victorian-era building a few miles southwest of London whose lavish interiors have appeared as sets in Downton Abbey. During tea and sandwich breaks it was clear that the conference was a reunion for researchers who have worked in the field for decades, and the mood was friendly. But there was a schism between the scientists.
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In one camp were those who believed the bio-compass could be explained by magnetite, iron crystals in animal cells that enable the development of organs capable of detecting the geomagnetic field. In the second camp were those who believed magneto-reception is best explained as a biochemical reaction that is influenced by the geomagnetic field—a model of navigation that depends on quantum physics. Although some of these scientists maintained that the bio-compass might involve a combination of mechanisms, many scientists at the conference had focused entire laboratory budgets on proving one hypothesis over the other, turning the search for the bio-compass into a scientific race. There was a lot at stake, not only the distinction of solving a problem that science has thus far been unable to solve but also potentially widespread applications for technology and medicine. The discovery of the bio-compass mechanism, for instance, could give momentum to the emerging field of quantum biology, the idea that quantum mechanics is more than “the deep substrate on which biology exists” but is actually the mechanism behind many biological phenomena, or it could launch a new era of magnetogenetics—the ability to control molecules in cells using magnetic fields.
It was Kirschvink who discovered the mineral called magnetite, a naturally occurring oxide of iron, in honeybees and homing pigeons as a PhD student at Princeton University, and soon thereafter he presented magnetite as the basis of a bio-compass in animals. Just a few crystals of magnetite, he wrote, needed to be present in a cell in order to detect the geomagnetic field. Energetic and outspoken, he remains a firm believer in the magnetite hypothesis of animal navigation. It is, he explained, the most rational evolutionary pathway for migratory behavior seen in the full range of animals. Natural selection took something that worked marginally—the receptivity of magnetite to the magnetic field—and through mutation and gene replication made it better and better until it produced navigational wizards such as the bar-tailed godwit. “You have to be able to build these things step by step. You have to have something to select for it,” he said. “You can do that with a magnet easily.”
The presence of magnetite in so many animals does seem like sure proof of the bio-compass. Throughout the 2000s a lot of researchers honed in on the presence of magnetite in olfactory cells of rainbow trout and brains of mole rats, as well as in the upper beaks of homing pigeons, as potential magneto-receptors. But then a team of scientists at the Institute of Molecular Pathology in Vienna took a closer look, slicing the beaks of hundreds of pigeons and staining them to detect iron-rich cells, and they found big discrepancies in the number of cells present. Some pigeons had a couple hundred while others had tens of thousands. The likely explanation was that the cells were simply the product of an immune response in the birds’ white blood cells. This doesn’t mean that the magnetite hypothesis is dead—far from it. “One equivalent of a magnetic bacteria can give a whale a compass. One cell,” said Kirschvink. “Good luck finding it.”
Around the same time that Kirschvink was finding magnetite in honeybees, a German physicist by the name of Klaus Schulten was looking at how radical pairs, two molecules each with an unpaired electron, could be responsive to magnetic fields. When the two electrons in a radical pair are correlated—in a state of either entanglement or coherence, meaning particles or waves affect one another even when separated over distances or split—the magnetic field is capable of modulating the electrons’ spinning motion. Two years later, Schulten published a second paper suggesting that this phenomenon might be the basis of a biomagnetic sensor in birds, a kind of “chemical compass,” he wrote, that was triggered when light caused an electron transfer reaction, generating radical pairs, that was then influenced by the external magnetic field.
For the next twenty years, no one knew where such a radical pair reaction might take place in animals. “It was clear that the radical pair mechanism was genuine,” Peter Hore, a professor of physical and theoretical chemistry at Oxford University, told me, “but highly speculative that it might happen inside a bird’s body.” Then in 2000 Schulten proposed a newly discovered protein called cryptochrome, which was found in plants and believed to regulate growth during photosynthesis. Cryptochrome proteins are a kind of flavoprotein that is receptive to blue light; they have since been found in bacteria, the retinas of monarch butterflies, fruit flies, frogs, birds, and even humans. And they are the only candidate thus far that has the right properties for what some are calling the quantum compass.
Hore’s research is focused on the behavior of radical pairs, and he became interested in testing the cryptochrome hypothesis after Schulten presented it. Genteel, with white hair and thin wire-framed glasses, Hore explained to me during the conference how difficult it is to design a “killer experiment.” While researchers can show that radical pairs produced in the proteins are sensitive to magnetic fields, the weakest magnetic field capable of affecting cryptochrome is still twenty times stronger than the earth’s magnetic field: no one has yet shown how these radical pairs can respond to earth’s extremely weak geomagnetic field. At least part of the problem is that it has been nearly impossible to reproduce the actual conditions of the cell for experimentation. Hore predicts that proving cryptochrome as the bio-compass will require at least another five and perhaps as many as twenty years of research. If and when that day comes, it will constitute a critical contribution to a new field of quantum biology, the study of quantum effects in living organisms.
The idea that nature may have harnessed quantum mechanics in the course of evolution is compelling and controversial. There is now, for instance, evidence that quantum dynamics are involved in photosynthesis, when photons are absorbed and transferred to a cell’s reaction center, creating electron excitation. Discovering more examples may lead to new quantum technologies. “The hope is that if these things are genuinely quantum biology,” Hore said, “maybe we can learn lessons that would enable us to make better magnetic senses or more efficient solar cells using principles from nature.”
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The 2011 study of humpback whales concluded that magnetism alone couldn’t explain the animals’ migration, because there was a lack of any consistent relationship between their direction of travel and the magnetic inclination or declination. And I found a small group of researchers at the London conference who were skeptical of magnetism as a universal explanation for animal navigation. Kira Delmore is a young Canadian biologist at the Max Planck Institute for Evolutionary Biology, whose research focuses on the Swainson thrush, of which there are two different subspecies, each with a different migratory route. One travels along the west coast of North America to Central America and the other over the Midwest. Delmore wanted to know if by using a combination of geolocation gadgets and genetic sequencing she could find out whether the birds’ different migratory behaviors were associated with particular genetic traits. In other words, could migratory orientation be explained by genetics? After years of research, her data showed that a bird’s decision to go south or southeast does have a genetic basis. “Migration is such a complex behavior, the idea that there is a gene that might say whether I should go left or I should go right, if that’s genomic, it boggles my mind,” she said.
Hugh Dingle has proposed that evolution created what he calls “migratory syndromes,” made up of a combination of behaviors and physiologies such as the suppression of maintenance activities, the use of fat as fuel, and navigation, and that each syndrome is shared across species and defines them as migratory. The definition of the word syndrome is revealing. It comes from the Greek sun, meaning “together,” and dramein, “to run.” But in the mid-sixteenth century, syndrome also became a medical term referring to a condition, illness, disorder, or sickness. Maybe that is what migratory syndrome feels like for the snow goose driven north to the Arctic each spring: not like a choice but like a powerful compulsion. In 1702 the ornithologist Ferdinand von Pernau described feathered migrants as forced to depart because of a “hidden drive at the right time.” In the late eighteenth century, natur
alist Johann Andreas Naumann kept golden orioles and pied flycatchers in a room, cutting a small hole in the door so that come winter he could watch them become agitated and restlessly try to escape their captivity. Charles Darwin once wrote about how John James Audubon kept a “pinioned wild goose in confinement, and when the period of migration arrived, it became extremely restless, like all other migratory birds under similar circumstances; and at last it escaped.” What inner longings steer a goose on its long journey north? What forces propel it there? These feelings or intuitions aren’t alien to our own human experience. Indeed the Swiss-American psychologist Elisabeth Kübler-Ross likened the hidden drives in animals and men to one another. As a young woman she traveled by ship from Europe to America, a place she had never been before, and during the journey wrote in her journal, “How do these geese know when to fly to the sun? Who tells them the seasons? How do we, humans, know when it is time to move on? As with the migrant birds, so surely with us, there is a voice within, if only we would listen to it, that tells us so certainly when to go forth into the unknown.”
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