Pattern Formation: An Integument Paradigm

Patterns can be defined as order embedded in randomness: they can appear as spatial arrangements or temporal series. In repetitive patterning, the elements may appear identical or with variations. Patterns exist in the physical world as well as in living systems. In the 'physical world', patterns can emerge from apparent chaos or randomness of the physical world, at different levels, revealing the physical and chemical processes underlying their formation. We are all familiar with patterns in clouds, water waves, rock layers, sand dunes, and so on. In the 'biological world', we can also appreciate patterns at different hierarchical levels: from molecular pathways, genome organization, developmental interactions, tissues, organs, body plans, to the level of animal behavior. At the genomic level, the sequential arrangement of nucleotides stores the information of each genome. At the multicellular level, different cell types and tissues are organized into different body plans. At the organism level, apparent patterns can be seen in leopard spots, zebra stripes, peacock feathers, cephalopod body patterning, and so on. At the level of behavior, humans can create sophisticated patterns, as seen in ancient architecture (e.g., pyramid), or an array of symbols or syllables (e.g., language, music) created at the dawn of civilization. In plants, we can also appreciate flower patterns, leaf shapes, tree branching patterns, and so on. Here, we discuss spatial and temporal patterns in animals and use skin appendage organs as examples since their patterns are most obvious to us.