Morphogenetic field


 * This article is about the mainstream developmental biology concept. For Rupert Sheldrake's concept of the same name see the corresponding section of Morphic field.

In developmental biology, a morphogenetic field is a group of cells able to respond to discrete, localized biochemical signals leading to the development of specific morphological structures or organs. The spatial and temporal extent of the embryonic fields are dynamic, and within the field is a collection of interacting cells out of which a particular organ is formed. As a group, the cells within a given morphogenetic field are constrained &mdash; i.e. cells in a limb field will become a limb tissue, those in a cardiac field will become heart tissue. Importantly, however, the specific cellular programming of individual cells in a field is flexible: an individual cell in a cardiac field can be redirected via cell-to-cell signaling to replace specific damaged or missing cells. Imaginal discs in insect larvae are examples of morphogenetic fields.

Historical development
The concept of the morphogenetic field was foundational for the study of embryological development in the early twentieth century. The notion was first introduced by Alexander G. Gurwitsch in 1910. Experimental evidence was given by Ross Granville Harrison, with experiments transplanting fragments of a newt embryo into different locations. In this way Harrison was able to identify fields of cells producing organs such as limbs, tail and gills. Furthermore, he was able to show that these fields could be fragmented, or have undifferentiated cells added, and a complete normal final structure would still result.

It was thus considered that the field of cells, rather than individual cells themselves, were patterned for subsequent development of particular organs. The field concept was developed further by Hans Spemann, who was a friend of Harrison, and then by Paul Weiss and others.

In the 1930s, the work of geneticists, especially Thomas Hunt Morgan, revealed the importance of chromosomes and genes for controlling development, and with the rise of the new synthesis in evolutionary biology, the field concept took back stage. Morgan was a particularly harsh critic of fields, since it was then considered that the gene and the field were competitors for the proper unit of ontogeny. With the discovery and mapping of master control genes, such as the homeobox genes, the pre-eminence of genes seemed assured.

In the late twentieth century, the field concept was "rediscovered" as a useful part of developmental biology. It was found, for example, that different mutations could cause the same malformations. This suggested that the mutations were impacting a complex of structures as a unit, and this unit corresponded to the field of classical embryology. Scott Gilbert proposes that the morphogenetic field is a middle ground between genes and evolution. That is, genes act upon fields, which then act upon the developing organism.

Jessica Bolker describes morphogenetic fields not merely incipient structures or organs, but as dynamic entities with their own localized development processes, which are central to the emerging field of evolutionary development ("evo-devo").