Reviews of "Lifecode" by Stuart Pivar

R. M. Hazen, Carnegie Institution

Pivar and colleagues propose a topological model of embryogenesis that is based on the properties of a toroidal surface. The principal evidence for this hypothesis consists of topological congruencies of a mechanical latex and polymer model (toroidal balloons) with observed embryological forms. The claim is made that this toroidal form arises during development from a process of self-organization. To me, the most intriguing and original aspects of this work are the design of the toroidal model and the closely-observed characterizations of the modes of its deformation (for example in the Hall et al. manuscript, pages 2-3 and Plate 1). I am not an expert in this area of topology and mechanics, but I'm sure there is a place for a more rigorous mathematical exploration of the relationships among such variables as length, width, viscosity, forces, and resultant segmented morphology. However, even the qualitative presentation is fascinating and seems worthy of publication. The extension of the mechanical model to embryo morphogenesis is also intriguing and would seem to bear further study, perhaps with photographic documentation. As drawn in the many fine illustrations, there does appear to be a correspondence between the segmented model forms of Plate 1 of the article and volume to early stages of embryo development. Plate 10 is especially dramatic and has some of the gratifying aesthetic quality typified by the best 19th-century natural history illustration. It would be nice to see corresponding embryo photographs. Finally, I am sympathetic to the references to "self-organized structures" as an underlying theme to aspects of embryo development. To me, that phrase implies that individual cells are responding to local (presumably chemical and mechanical) stimuli in their division, shape, apoptosis, etc. This idea makes a lot of sense, and it points to specific experiments that can be performed on developing embryos. After all, if an embryological form can be altered by specific chemical or mechanical stimuli, then we'll gain insight into development. In fact, I suspect that there's a significant literature on exactly this kind of experiment. Taken together, these three aspects the behavior of the mechanical toroid, the observations of early embryonic stages, and the concept of self-organization might conceivably be woven together more tightly to produce a predictive model of the evolutionary sequence of embryo development.

Robert Hazen is a leader in origin of life science and  NASA Astrobiology Institute affiliate.

Dr. Dimitar Sasselov

"I believe the model is plausible. I will defend it."
 

Dimitar Sasselov is the director of the Harvard initiative for the study of the origins of life.
 

Dr. Brain Goodwin

"This pure structuralist model of life origin is a contribution to biological taxonomy."

 
Brian Goodwin is the author of How the Leopard Changed its Spots
 

Dr. Neil de Grasse Tyson

Another possibility is that life has encoding that has nothing to do with DNA. That would be more important for biology than finding other life with DNA, because it would be a way to encode life that no one has dreamt of before No mere mathematical curiosity, this physically plausible model should be investigated seriously by biologists.

Neil de Grasse Tyson is the  director of the Hayden Planetarium