Sponge Bobs Upward in Respect
The simplest group of multicellular animals, the sponges, is not so simple. “Researchers have long regarded sponges as the most primitive form of animal life,” wrote Helen Pilcher in Nature;1 “At first glance, sponges seem simple. They have no gut, no brain, no obvious front or back, left or right. Adults pump water through a system of canals and cavities to extract food.” That apparent simplicity belies some pretty advanced technologies possessed by these creatures. Pilcher mentions several (emphasis added in all quotes):
- They contain a diversity of cell types; one species contains “at least 11 specialized cell types arranged in a particular pattern.”
- They contain collar cells with whip-like tails that create currents in the body to ingest food and excrete waste.
- They produce sperm and egg cells.
- They have an epithelial layer that provides protection.
- They make use of a cellular adhesive, integrin, that works with collagen to provide a tether.
- They communicate with signals that tell developing embryonic cells where to go. “Like more complex animals,” Pilcher writes, “sponges solve this problem by using specific molecules to guide differentiation and migration as the cells develop in their embryos.”
These and other characteristics of sponges suggest to evolutionary biologists that the genetic toolkit for these functions was already present in a putative unicellular ancestor before the first metazoan emerged. It seems that the unknown ancestor must have already been “a sophisticated creature.”
Later, in Science,2 more marvels about the sponge called Venus Flower Basket were revealed (see 03/01/2004 entry). Not only does it know how to create high-performance, flexible fiber optic cable at low temperatures; now, says MSNBC News, it is able to “build glass cages that have biologists and materials scientists oohing, ahhing and taking notes for future bio-inspired engineering projects and materials.” Reporter Daniel B. Kane continues, “These glass cages have at least seven levels of structural organization, many of which follow basic principles of mechanical engineering,” referring to the paper by Aizenberg et al. who wrote in the abstract, “The ensuing design overcomes the brittleness of its constituent material, glass, and shows outstanding mechanical rigidity and stability. The mechanical benefits of each of seven identified hierarchical levels and their comparison with common mechanical engineering strategies are discussed.” Their opening paragraph puts this discovery in context:
Nature fascinates scientists and engineers with numerous examples of exceptionally strong building materials. These materials often show complex hierarchical organization from the nanometer to the macroscopic scale. Every structural level contributes to the mechanical stability and toughness of the resulting design. For instance, the subtle interplay between the lattice structure, fibril structure, and cellulose is responsible for the remarkable properties of wood. In particular, it consists of parallel hollow tubes, the wood cells, which are reinforced by nanometer-thick cellulose fibrils wound helically around the cell to adjust the material as needed. Deformation occurs by shearing of a matrix rich in hemicelluloses and lignin, “gluing” neighboring fibrils, and allowing a stick-slip movement of the fibrils. Wood is an example that shows the wide range of mechanical performance achievable by constructing with fibers. Bone is another example of a hierarchically assembled fibrous material. Its strength critically depends on the interplay between different structural levels—from the molecular/nanoscale interaction between crystallites of calcium phosphate and an organic framework, through the micrometer-scale assembly of collagen fibrils, to the millimeter-level organization of lamellar bone. Whereas wood is fully organic material, bone is a composite, with about half organic and half mineral components tightly interconnected at the nanoscale. However, nature has also evolved almost pure mineral structures, which—despite the inherent brittleness of most minerals—are tough enough to serve as protection for the organism. In mollusk nacre, for example, the toughening effect is due to well-defined nanolayers of organics at the interfaces between microtablets of calcium carbonate. In such structures, the stiff components (usually mineral) absorb the bulk of the externally applied loads. The organic layers, in turn, provide toughness, prevent the spread of the cracks into the interior of the structure, and even confer a remarkable capacity for recovery after deformation.
From here, they discuss how the Venus Flower Basket builds its glass house from the bottom up with each level of organization contributing to the high performance of the end product. Their concluding paragraph seems to contain mixed metaphors: design and evolution—
The structural complexity of the glass skeleton in the sponge Euplectella sp. is an example of nature’s ability to improve inherently poor building materials [e.g., glass]. The exceptional mechanical stability of the skeleton arises from the successive hierarchical assembly of the constituent glass from the nanometer to the macroscopic scale. The resultant structure might be regarded as a textbook example in mechanical engineering, because the seven hierarchical levels in the sponge skeleton represent major fundamental construction strategies such as laminated structures, fiber-reinforced composites, bundled beams, and diagonally reinforced square-grid cells, to name a few. We conclude that the Euplectella sp. skeletal system is designed to provide structural stability at minimum cost, a common theme in biological systems where critical resources are often limited. We believe that the study of the structural complexity of unique biological materials and the underlying mechanisms of their synthesis will help us understand how organisms evolved their sophisticated structures for survival and adaptation and ultimately will offer new materials concepts and design solutions.
In the same issue of Science,3 John Currey provided details on six of the levels of organization investigated by Aizenberg et al.:
Euplectella is a deepwater sponge whose glassy skeleton is a hollow cylinder. On the first level of structural hierarchy, nanometer-sized particles of silica are arranged around an organic axial filament. On the second level, alternating layers of silica and organic material form spicules. On the third level, these small spicules are bundled together to form larger spicules. On the fourth level, the larger spicules are arranged in a grid, with struts in longitudinal, circumferential, and diagonal directions, resisting all load modes (see the figure). In the mature animal, these larger spicules are coated with a cementing layer of silica. On the fifth level, this grid is wrapped into a curved cylinder. Finally, on the sixth level, helical surface ridges further resist torsion and stiffen the structure.
Currey was most intrigued with level four, a “most remarkable feature” with its cross-beams and struts providing load strength and protection from shear. The MSNBC article contains three photos illustrating the architecture in this “primitive” metazoan. Aizenberg told the reporter, “It puzzles me. In my wildest dreams I can’t imagine how these fibers are assembled to make the nearly perfect, highly regular square cells, diagonal supports and surface ridges of the cage.” Despite the simplicity of the sponge’s anatomy, possessing no brain or nervous system, these structures represent “some of the most complex and diverse skeletal systems known.”
1Helen Pilcher, “Back to our roots,” Nature 435, 1022-1023 (23 June 2005) | doi: 10.1038/4351022a.
2Aizenberg et al., “Skeleton of Euplectella sp.: Structural Hierarchy from the Nanoscale to the Macroscale,” Science, Vol 309, Issue 5732, 275-278 , 8 July 2005, [DOI: 10.1126/science.1112255]
3John D. Currey, “Materials Science: Hierarchies in Biomineral Structures,” Science, Vol 309, Issue 5732, 253-254 , 8 July 2005, [DOI: 10.1126/science.1113954].
Wild dreams and imagination are not science; they indicate that Aizenberg is in a philosophical slumber by attributing engineering to evolution. If evolution produced this sponge’s architecture, as assumed by faith by these investigators, each stage must have contributed to an end result. Stage four would not help unless the lower stages in the hierarchy were already conferring their benefits; it would be like trying to build struts out of crumbly styrofoam or bits of broken glass. But end results are prohibited by evolutionary theory which stresses that evolving organisms have no goal in mind. In the Nature article, Simon Conway Morris extolled Tinker Bell: “Evolution is an extremely dynamic system and paradoxically a very lazy one. It will co-opt whatever it can.” Evolutionists preach that laziness and tinkering with available parts produced wonders of engineering that are the envy of materials science.
It’s time to replace Darwin’s tomb in Westminster Abbey with Kepler’s, and change the objective of science from explaining away God back to thinking God’s thoughts after Him. This will lead to productive inquiry in science. Notice that the researchers here were oohing and ahhing not over Charlie’s little outworn myth, but over the engineering design apparent in the lowly sponge.