Morphogen gradient theories have enjoyed considerable popularity since the beginning of this century, but conclusive evidence for a role of morphogens in controlling multicellular development has been elusive. Recently, work on three secreted signalling proteins, Activin in Xenopus, and Wingless and Dpp in Drosophila, has stongly suggested that these proteins function as morphogens. In order to define a factor as a morphogen, it is necessary to show firstly, that it has a direct effect on target cells and secondly, that it (...) affects the development of target cells in a concentration‐dependent manner. With these criteria in mind, the evidence available for a variety of proposed morphogens is discussed. While the evidence is not conclusive in most of the cases considered, there is a strong case in favour of the three proteins mentioned above, which suggests that morphogens are potentially of general importance in controlling the development of multicellular organisms. (shrink)

If, as is universally acknowledged, the proper goal of the mathematical sciences is the discovery of the least possible number of principles from which the universal laws of empirically given facts emerge with mathematical necessity, and thus the discovery of principles equivalent to those empirical facts, then it must appear as a duty of indubitable importance to reflect carefully on the principles that have already surfaced with some certainty in one area of the natural sciences and present them in a (...) form that really fulfills the equivalence requirement. (shrink)

Almost all admit that there is beauty in the natural world. Many suspect that such beauty is more than an adornment of nature. Few in our contemporary world suggest that this beauty is an empirical principle of the natural world itself and instead relegate beauty to the eye and mind of the beholder. Guided by theological and scientific insight, the authors propose that such exclusion is no longer tenable, at least in the data of modern biology and in our view (...) of the natural world in general. More important, we believe an empirical aesthetics exists that can help guide experimental design and development of computational models in biology. Moreover, because theology and science can both contribute toward and equally profit from such an aesthetics, we propose that this empirical aesthetics provides the foundation for a living synergy between theology and science. (shrink)