Conclusion

Minor extensions or combination of reactions that are based on self-enhancement and one or two antagonistic reactions can generate a remarkable variability of pattern. Thus, part of the spatial complexity of a developing organism may be generated by an appropriate combination of elements taken from a basic toolbox.

An essential property in these models is their inherent capability for self-regulation. This accounts for the fact that development is a very robust process up to the point that normal development can remain possible even after removal of some essential parts (Figs. 3 and 8). By this self-corrections the propagation of errors into subsequent levels can be avoided. Thus, an understanding of the dynamics of the interactions on which pattern formation is based provides a key for the reliability that is characteristic for many developmental processes.

Acknowledgement: I wish to express my sincere thanks to Prof. Alfred Gierer. Much of the basic work described here emerged from a fruitful collaboration over many years.