LAUSR

Published in 1917, “On Growth and Form” was the culmination of over twenty years of thought by the Scottish bio-mathematician, D’Arcy Wentworth Thompson, about the relationship between living things and physical phenomena. One striking aspect of the book is its extraordinary breadth, covering topics as diverse as temperature regulation, the growth of trees, and organ shape. Of course, it is arguably most famous for the development of the theory of transformations, whereby different biological forms can be explained through coordinate transformations of another form. The simplicity of such an idea – yet the complexity that can be derived from it – is a hallmark of Thompson’s approach. These ideas have endured the test of time and now, a century after the first publication of “On Growth and Form”, seems an appropriate time to reflect on this legacy. In particular, what influence do Thompson’s ideas still have on developmental biology? This special commemorative edition ofMechanisms of Development was commissioned in partnership with the International Society of Developmental Biology to coincide with the D’Arcy Thompson Centenary Symposium at its 18 Congress, held in Singapore June 2017. In it, five researchers give their personal perspective on the impact of “On Growth and Form” on their own work and their respective research fields. Olivier Hamant discusses how Thompson’s ideas motivated the field of “mechano-devo”, and the rise of interdisciplinary developmental biology. In particular, he outlines the importance of considering force when investigating processes such as organ scaling. A critical point is that the underlying physics is the same in both plant and animal cells. For example, membrane tension is critical across phyla and epidermal tension is essential for adhesion. This matches with Thompson’s ideas – the biophysics stands above the underlying specifics of the biology. Thomas Gregor looks at the future challenges facing the burgeoning field of quantitative biology, particularly with regard to development. A key point he raises is the use of theory to make testable predictions in vivo. As an example, he describes Berg and Purcell’s limits on information transfer during bacterial chemotaxis. He expands on this, and demonstrates how such ideas play an important role in gene regulation and cell fate. This demonstrates a critical point: the strength of theoretical approaches is that they are often not constrained to a particular system but can be applied across a range of biological fields. Timothy Saunders details how D’Arcy Thompson’s models of soap bubbles can effectively describe many observed phenomena – but yet also have limitations.With increased imaging quality, we can now observe living organisms for longer and with higher resolution and such analyses are revealing the inherently non-equilibrium nature of many biological systems. The development of tools – both experimental and theoretical – for probing non-equilibrium systems is going to be essential for understanding many biological systems. Carl-