(Originally published on the Access Research Network on the 28th Aug, 2008 as The Organocentric Illusion: The Biological Complexity Underlying Dynamic Systems)
Brian Goodwin died last week at the age of 78
Today much of evolutionary biology has focused on trying to establish how genes may have provided the raw material for natural selection to run its course (Ref 1, pp.1-2). In this genocentric view, inheritance through random mutation and selection is the basis upon which all of life and its ensuing diversity have arisen. Nevertheless several scientists including Open University biologist Brian Goodwin have challenged this view by postulating that organisms are built not only through genetic instruction but also through processes of dynamic organization that act independently of genes (Ref 1, pp.1-8). In his book How The Leopard Changed Its Spots, Goodwin outlines several key examples in nature that support his position. From the elegant concentric and spiral patterns of slime-mould amoebas to the dynamic mode of the mammalian heart and the brain, and finally to the ordering of haphazard ants into efficient, hard working colonies, (Ref 1, pp.43-76) Goodwin comes to the conclusion that in these systems, biological complexity has arisen through the ordering of dynamic systems independently of the action of genes. Experiments on the bacterial flagellum are yet another of his notable examples.
Bacterial flagellar filaments are made up of proteins called flagellins that fit together into repetitive, highly ordered arrays. The salmonella bacterium displays two types of flagella which are classified as ‘wavy’ or ‘curly’ depending on the degree of undulation present in the filament (Ref 1, pp.11-13). Experiments have shown that molecules taken from each of these different types of flagella seed their own formation- that is, wavy and curly flagellin will always assemble into their respective flagella forms (Ref 1, pp.11-13). This in itself is not remarkable. What is remarkable is that when wavy flagellin is mixed with curly fragments, these wavy flagellin molecules will assemble into curly flagella. In short, curly fragments can seed the formation of entire curly flagella when supplemented with wavy flagellin (Ref 1, pp.11-13). These results strongly suggest that changes between two different types of flagellar filament can arise independently of the genes that produce these filaments.
Perhaps Goodwin’s favorite illustration of this so-called organocentric origin of biological complexity is the acetabularia- a sea-dwelling, single-celled organism with a parasol-like structure that closely resembles a fluted coffee filter. In the acetabularia, structural complexity arises not from the blueprint of genetic instruction but rather from the organization of the cytoplasm into a shape that is dependent both upon the intrinsic nature of the cell itself and the immediate surroundings of the cell (Ref 1, pp. 77-114). In their own experiments, Goodwin and his colleagues have shown that the formation of these structures is highly dependent upon the interaction between calcium ions and the proteins that form the cytoskeleton. The cytoskeleton is a network of support structures that help to give the cell its rigidity and shape playing a role that is not too dissimilar from that of metal scaffolding holding up a tent.
Goodwin’s arguments on organocentricity contrast with those of evolutionary biologist Richard Dawkins who has written extensively on the overarching importance of the gene as the foundational source of life. According to Dawkins, all life forms are merely, “survival machines” that serve as, “lumbering robots” through which genes can achieve their own ends of replicating and surviving (see Ref 2, p.19). Genes are the ‘replicators’- the Darwinian ‘individuals’ that have chosen different ways of making a living (Ref 2, pp.21-24). Those genes that were most successful at surviving, we are told by Dawkins, will go on through successive generations to inhabit new bodies, in the process developing new strategies for survival (Ref 2, p.25). In Dawkins’ view our bodies are nothing more than the product of genes that are actively cooperating with each other and whose survival depends on how well they have predicted the sorts of environments that the body that they have taken residence in is going to experience (Ref 2, pp.51-56).
Through his own evidence Goodwin has done a formidable job in dismissing Dawkins’ purely reductionist stance. Nevertheless it is clear that the dynamic self-organization that Goodwin has observed relies on the presence of an already-existing complexity within the cell. A closer look at the process through which acetabularia establishes its shape, for example, reveals that the amount of calcium present in the cell is regulated by an elaborate set of pumps that sequester the calcium into storage chambers where special proteins can hold it in an inactive state (Ref 1, pp. 92-111).
Recent studies have demonstrated that calcium plays a number of roles within the cell and that there are strict limits on the amount of calcium that the cell can tolerate if proper function is to be maintained (Ref 1, pp.92-111). Moreover the cytoskeleton is itself an elaborate network of protein polymers. Some of these polymers provide rails not unlike train tracks that allow organelles to move within the cellular confines while others provide much of the cell’s own structural support. The cytoskeleton constantly shrinks and contracts as the cell adjusts to its external environment while also transporting proteins to cellular compartments where such proteins are needed. Rather impressively, in multi-cellular animals the entire cytoskeleton is responsive to proteins that span the cellular membrane some of which are able to detect the cell’s extra-cellular environment and make adjustments to the cytoskeleton accordingly (Ref 3, p.613).
Perhaps not to dissimilar to a national railway system but much more dynamic in its nature, the cytoskeleton is an impressive array of three different types of molecules- microtubules, which provide the cellular transportation network, and actin and intermediate filament proteins which supply the internal cellular structural support (Ref 3, p.613). It turns out that actin filaments are used by the microtubules as a kind of ‘guide-rope’ for ensuring that proteins are transported to their correct destination (Ref 4). How these microtubules attach to the actin filaments in mammalian cells was elucidated by a study headed by Rockefeller University biologist Elaine Fuchs. This study described the involvement of a little-known family of proteins called the actin cross-linking family (ACFs) that ensure the correct ‘coupling’ of the microtubules to actin (Ref 4). It is now well known that molecular motors called kinesins ferry cargo to different regions of the cell by moving along cytoskeletal filaments, not unlike cable cars moving along cables ferrying passengers to diverse destinations (Ref 5). We should expect similar structural and mechanistic roles to exist in the cytoskeleton of acetabularia.
So what of organocentricity? Clearly the dynamic organization that Goodwin has so vividly drawn our attention to is simply a manifestation of a complexity that is already present in living systems. Even the production of flagellin in bacteria requires machines- ribosomes- that synthesize the flagellin proteins from the genetic blueprint. The multi-component structure of the flagellar motor is likewise well-documented (Ref 6, pp.69-73). Within the cellular world there exist enormously complex molecular networks and biological machines. It is this complexity that has been the power behind the argument for intelligent involvement in biological design.
1. Brian Goodwin (1994), How The Leopard Changed It’s Spots: The Evolution Of Complexity, Princeton University Press, New Jersey, United States
2. Richard Dawkins (1976), The Selfish Gene, Oxford University Press, Oxford, UK
3. Bruce Alberts, Dennis Bray, Julian Lewis Martin Raff, Keith Roberts, James D Watson (1989), Molecular Biology of the Cell, Published by Garland Publishing Inc, New York, 2nd Ed
4. The review on the work done by Elaine Fuchs on ACF7 can be found in a News Release from the Rockefeller University entitled ‘Giant protein organizes the transportation railway system within cells’ which can be found on http://runews.rockefeller.edu/index.php?page=engine&id=68
5. Mikyung Yun, C.Eric Bronner, Cheon-Gil Park, Sun-Shin Cha, Hee-Won Park and Sharyn A. Endow (2003) Rotation of the stalk/neck and one head in a new crystal structure of the kinesin motor protein, Ncd EMBO J Vol. 22, pp. 5382-5389
6. Michael J Behe (1996), Darwin’s Black Box-The Biochemical Challenges to Evolution 1st Edition Published by Simon and Schuster, New York