Let's Reminisce: Persuading the human body to regenerate its limbs
Wouldn’t it be great if the human body could regenerate a missing limb? Michael Levin, a developmental biologist at Tufts University, believes it can be done. He studies how bodies grow, heal, and in some cases regenerate.
He has made a number of important discoveries by working on the planarian, a flatworm about two centimeters long. If you cut off its head, it grows a new one. Simultaneously, its severed head grows a new tail. In fact, researchers have discovered that no matter how many pieces you cut a planarian into—the record is 279—you will get that many new worms. Somehow each part knows what’s missing and builds it anew.
The most astonishing part is that Levin hasn’t touched the planarian’s genome. Instead, he’s changed the electrical signals among the worm’s cells. By altering this electric patterning, he revised the organism’s “memory” of what it was supposed to look like.
This is where possible applications to humans enter the conversation. Levin’s work is part of a convergence between biology and computer science. In the past 50 years, scientists have come to see the brain as a kind of computer. Levin extends this thinking to the body; he believes that mastering the code of electrical charges in its tissues will give scientists unprecedented control over how and where they grow.
Levin says that regeneration is not just for so-called lower animals. Deer can regenerate antlers; humans can regrow their liver. Human children below the age of approximately seven to eleven are able to regenerate their fingertips. So why couldn’t human-growth programs be activated for other body parts—severed limbs, failed organs, even brain tissue damaged by stroke?
Levin’s work involves a conceptual shift. The computers in our heads are often contrasted with the rest of the body; most of us don’t think of muscles and bones as making calculations. But how do our wounds “know” how to heal? How do the tissues of our unborn bodies differentiate and take shape without direction from a brain?
When a caterpillar becomes a moth, most of its brain liquefies and is rebuilt—and yet researchers have discovered that memories can be preserved across the metamorphosis. That suggests that limbs and tissues besides the brain might be able, at some primitive level, to remember, think, and act.
Levin’s work has appeared in textbooks and he publishes between thirty and forty papers a year. His collaborators include biologists, computer scientists, and philosophers. He is convincing a growing number of biologists that it is possible to decipher, and even speak, the bioelectric code.
Grasping the bioelectric code, Levin believes, will give us a new way of interacting with our bodies. And he is not alone in thinking that we will someday be able to regrow human limbs.
He and some other developmental biologists disagree only about how long it might take us to get there, and about how, exactly, regrowth would work. Other projects explore growing body parts in labs for transplantation; or 3-D-printing them whole; or injecting stem cells into residual limbs. The solution may eventually involve a medley of techniques.
Researchers disagree about the role that bioelectricity plays in morphogenesis. The consensus is that there are many things we still need to discover about how the process
works. Our intuitions tell us that it would be bad to be a machine, or a group of machines, but Levin’s work suggests precisely this reality. In his world, we’re robots all the way down.
Jerry Lincecum is a retired Austin College professor who now teaches classes for older adults who want to write their life stories. He welcomes your reminiscences on any subject: firstname.lastname@example.org.