A recent article at Aeon magazine proposed that one of the master symbols of twentieth century biology, the double-helix structure of DNA, should be replaced by the symbol of a feedback loop. Jamie Davis provides a quick tour of the ways that understanding DNA has failed to capture or explain the development of organisms. The technology to sequence the genomes of many organisms has only developed in the last two decades and the optimistic hope that once the sequences were completed we would then be able to understand the whole of the organism, the causes of diseases, and much more has been mostly dashed. It turns out that biology is much more complex than the genetic explorers expected.
The mid-twentieth century vision for biology was, according to Davis, strongly reductionist. Many of the major scientists of the time believed that understanding the structure of DNA would reveal the causes for diseases and the reveal the blueprint for life on Earth. Genes are important but the picture of a single gene causing X is slowly unraveling. Instead we are left with “‘the gene for protein a, that interacts with proteins b, c and d to allow a cell to undertake process p, that allows that cell to co‑ordinate with other cells to make body feature x’. The very length of the above phrase, and the weakness of the blueprint metaphor, emphasises a conceptual distance that is opening up between the molecular-scale, mechanical function of genes and the interesting large-scale features of bodies.”
In place of the double helix Davis suggests that we should reconsider an even older symbol for understanding life: the concept of the feedback loop. There are numerous examples of how genes and the proteins they create form part of a larger system that includes feedback loops which control the outcomes of life. For example skin develops by connecting the internal cytoskeletons of cells to other cells through a process of production and elimination. Cytoskeleton connections branch out in all directions, in some directions the connections meet with other cells, in other directions the connections go nowhere. The blank connections dissolve but the connections which meet other cells are reinforced and become the bonds between individual skin cells. Other examples from the development of blood capillaries, drainage ducts in the kidneys, or the healing of skin all tell similar tales of self-organization and feedback.
Complexity theory and artificial life get their moment in the sun as other examples of how feedback loops play out in the real world. The flocking and schooling behavior of birds and fish can be simulated on computers using simple algorithms at the individual level - such as attraction, repulsion, alignment, and searching. Ecosystems seem to operate on some of the same principles of self-regulation
All of these examples, and many more like them, turn out to have something in common when analysed at the mechanistic level: in each case, what has been achieved so far by the system is used to control its current behaviour. This type of control is called feedback, and is represented by a loop feeding information from the output of a process back to its input.
After reading this article I was reminded of three connections from my own intellectual adventures. The first was a connection to the ideas of cybernetics introduced by Norbert Weiner in the middle of the twentieth century. I remember being struck by how much of Weiner’s initial work on cybernetics was driven by his work on weapons control systems during World War Two. The feedback loop needed to aim an artillery piece at a rapidly moving aircraft became the basis for describing both human and animal systems. Weiner’s work went on to have important impacts in systems theory and from there into ecological studies.
The other connection I made was to an idea I had twenty years ago during college. I thought then, and still do now, that much of our aesthetic appreciation of the arts depends on the idea of the loop. Music clearly has many aspects of looping involved. Rhythm and harmony are often looped in music. One of the big challenges in free jazz and some parts of modern classical music is the deliberate upsetting of the loops we have been taught to expect from music. Electronic feedback is a key ingredient in many genres of rock music.
Other arts, such as painting, have also troubled the idea of looping during the twentieth century. My favorite example is the work of Jackson Pollack with his obvious loops of dripping paint. But other abstract expressionists, like Mark Rothko, can also be included in this lineage. For Rothko, the layering of paint becomes the loop/self-reference which makes art possible. Pop art, like Warhol, feeds back on culture by appropriating commercial images like the Campbell Soup Can. Some earlier musing on Barnett Newman and Dieter Roth.
The final connection I’ll mention is to the strange loop theory of consciousness proposed by Douglas Hofstadter. For Hofstadter the feedback of our own internal mental representations becomes the root of our own consciousness.
Loops are interesting concepts which seem to crop up in sometimes unexpected places.