One of the greatest mysteries in biology is the question of how some animals are able to sense Earth’s magnetic field, and, in turn, use it as a compass to determine their spatial orientation. Migratory birds, famously, use this mysterious “magnetoreception” to navigate. Now, in a significant breakthrough, scientists say they may know how the birds use this sense. And it all comes down to quantum physics.
Henrik Mouritsen at The University of Oldenburg in Germany led the scientists behind the magnetoreception study, which they published in the journal Nature. The scientists were actually working off a hypothesis first proposed by a physicist back in the ’70s; one that proposed the idea that magnetoreceptive animals use light-sensitive molecules to sense Earth’s magnetic field.
The idea behind the strange sense organ is this: Light-sensitive molecules—called cryptochromes—in the birds’ eyes each contain two unpaired electrons. And when they absorb light, the electrons take on different “spin” states. (Spin in the context of quantum physics is an intrinsic form of angular momentum elementary particles carry.) Depending upon which spin state the electrons inside the molecules are in, the birds can, consequently, locate Earth’s magnetic field.
Observations of magnetic sensitivity in a protein from the eyes of the European robin indicate that it may function as part of a ‘living compass’ and allow migratory songbirds to navigate using the Earth’s magnetic field, according to a Nature paper. https://t.co/MTTa4wKTb8 pic.twitter.com/u0teAwWylZ— nature (@Nature) June 24, 2021
Put another way, the electrons inside of the cryptochromes serve as “scales” of sorts. They intrinsically exist between both spin states—the “singlet” and “triplet” states—but tip toward one or the other when they encounter a magnetic field.
To see if this was indeed how cryptochromes work in migratory birds, the scientists studied the molecules in the lab. The scientists took cryptochromes from European robins, and tested them to see how they interacted with light. And, lo and behold, light did indeed cause the electrons to tip toward one or the other spin state. Incredibly, the scientists also looked at chickens’ cryptochromes and found they were far less sensitive than the robins’. A finding that supports the idea migratory birds use the cryptochromes to migrate, as chickens obviously aren’t fans of flying anywhere.
“Not only could we show that the electrons jump inside the molecule exactly as predicted by the quantum chemists in theory, we could also show the photochemistry of that radical was actually magnetically sensitive,” Mouritsen says in a Nature explainer video (top). “Now, it’s not a hypothesis this molecule is magnetically sensitive, we can see it’s magnetically sensitive,” he adds.
Perhaps the most fascinating aspect of the discovery is the possibility migratory birds literally see Earth’s magnetic field. Mouritsen proposes the idea that they see it as a shadow that layers over the world in the visual spectrum. And, frankly, all we can say at this point is that when we get our Neuralinks, we want them to have this feature.
Feature image: nature video