A visual aid, representing a multidimensional space that includes the dimension of time, devised by Conrad H. Waddington (1905-1975) to capture some of the main features of genotype-phenotype interaction during development (i.e., those of epigenetics) such as canalization, equifinality, and homeorhesis (see figure below). The landscape varies between individuals, but nevertheless maintains its basic shape of a sloping surface ending in the same valley. No matter how the phenotype (depicted by a rolling ball) traverses the landscape, it will always end up in that valley. It is interesting to note that Waddington originally trained as a geologist and thus drew on this experience to devise this visual analogy between a geographical structure consisting of hills and intersecting valleys on the one hand and ontogenetic development and the other.
Waddington used a visual metaphor to his illustrate his epigenetic landscape as representing a dynamical developmental process. The topography of the landscape in terms of valleys and hills stands for the total genotype of the developing system. The ball rolling down the landscape can be regarded as a phenotypic manifestation at the level of a cell, an organ, an individual, or even a species. The layout of the landscape can vary at different levels of organization such as that for morphological systems, individual organisms and species, and perhaps even between cultures. It encapsulates a number of features designed to cater for organism-environment interactions, and is to be considered as a multidimensional space that includes a time dimension. Coursing through this space are a number of trajectories or developmental pathways that are represented by interlinked valleys. These are referred to as chreods and imply stabilised trajectories of species-characteristic developmental sequences, each with their own differentiated end state. Stability is catered for by what Waddington called ‘canalization’ and ‘homeorhesis’, with the depth of a valley indicating the degree of canalization, and together with homeorhesis ensuring equifinality. It is important to recognize that the epigenetic landscape is nothing more than a descriptive model or analogy, and in no way serves to explain ontogenetic development. However, catastrophe theory, the brain child of René F. Thom (1923-2002), was directly inspired by the epigenetic landscape.
See Analogy (biology), Canalization, Catastrophe theory, Diachronic biology, Epigenesis, Epigenetics, Equifinality, Homeorhesis