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Multicellular organisms

Leo W. Buss (1987) in a pioneering monograph has explored the transition from unicellular to multicellular organisms in great detail, and has exemplified how the competition among cells for differential propagation by fission created obstacles to the emergence of multicellular organisms with cellular differentiation (i.e., division of labor). He says:
"The path from a unicellular condition to a multicellular one has been well-traveled. Of the same 23 monophyletic protist groups, fully 17 have multicellular representatives. The path from multicellularity to cellular differentiation, however, proved a far less porous filter. Of the 17 multicellular taxa, only 3 groups—the plants, the fungi, and the animals—have developed cellular differentiation in more than a handful of species. With the evolution of cellular differentiation, kingdoms were made of some protist groups; yet we know virtually nothing as to why this transition was closed to all but a few taxa." (Buss, 1987, p. 70
In agreement with Turchin's definition of Metasystem Transition, Buss portrays the first stage of multicellularity without differentiation of function, except for accidents of location in the adhering mass. With differentiation comes the distinction between germ cells and somatic cells. Somehow the germ cells exchange proliferation by fission within the organism for reproduction by seed across generations, and the specialized somatic cells gain in reproductive opportunities by fission within the organism. It helps in achieving differentiated multicellularity that all of the cells are identical twins in terms of chromosomal genes (implying a shared control). This has not removed the competition among cells for reproduction by fission. Adaptive distribution of such specialized cell proliferation requires additional controls. These are not under any centralized coordination, but are achieved through a widely distributed variety of inducing and inhibiting adjacencies. Keeping these controls tuned so that the integrated division of labor which produces a multicellular-organismic functionality is preserved requires a node of selection at the whole organism level. Such a node was also a prerequisite for its development. This node is implemented by differential propagation of the seeds produced by the germ cells.

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Copyright© 1995 Principia Cybernetica - Referencing this page

Author
D. T. Campbell

Date
Apr 25, 1995 (modified)
Sep 1991 (created)

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