When D'Arcy Thompson penned his 1917 book On Growth and Form he boldly declared that the morphologist — devoted to understanding the structure of organisms — is ipso facto a student of physical science. His meaning was clear: the growth of complex structures mediating specific biological function is underpinned by an intrinsic mechanics, an appreciation of which is crucial to a broader understanding of both form and function.

Thierry Savin and colleagues refer to Thompson's tome in their investigation, published in Nature, of the elaborate looped morphology that arises in the vertebrate gut (Nature 476, 57–62; 2011). Using experiment, simulation, and an innovative physical mock-up comprising rubber tubing stitched to latex, they have examined the forces arising from relative growth between the gut tube and a neighbouring sheet of tissue known as the dorsal mesentery. The study reveals a mechanism for the formation of loops based on differential strain between the two tissues.

Credit: © SPL

This is a timely nod to Thompson's century-old ideas, given the recent surge of physicists and mathematicians into the biological sciences, problem-solving artillery engaged. In another paper, published in Physical Review Letters, Edouard Hannezo, Jacques Prost and Jean-Francçois Joanny adopt a similarly mechanical approach to understanding the complex structures seen lining the small intestine (pictured), invoking an analogy with the buckling of metallic plates under compression (Phys. Rev. Lett. 107, 078104; 2011). They have developed a model that implicates cellular division and death as sources of internal stress, which in turn influences morphology and induces mechanical feedback on organ and tissue development.

One of the most interesting aspects of Thompson's treatise is an emphasis on the degree to which structures in different tissues and organisms can be related to one another by means of mathematical transformation. Both of the new papers offer striking evidence to this effect. For Savin et al., scaling arguments for the size, number and radius of loops account for qualitative and quantitative variation across different species, including chick, quail, finch and mouse. In a similar spirit, Hannezo and colleagues report that by tuning their model for the morphology of the small intestine, the markedly different structures populating the colon can also be reproduced.

The upshot of this and related work is that macroscopic mechanics drives morphology during the formation of tissues and organisms — bringing the formalism of physics to bear on long-standing problems in developmental biology.