"In some colony like Volvox there once lay hidden the secret of the body and mind of man." Huxley 1912
(1) They comprise a group of closely related organisms that range in complexity from unicellular forms, undifferentiated colonies, to true multicellular individuals with completely differentiated germ and somatic cells.
(2) They are of such recent origin (in geological time) that there is hope that its various members may still retain within their genomes traces of the genetic changes that permitted transitions from one level of organizational complexity to the next.
(3) The transitions in complexity have occurred more than once, thus raising the hope that the genetic changes and selective factors required for these transitions may be analyzed.
(4) Stable mutant forms of V. carteri with disrupted germ-soma separation have been isolated and can serve to elucidate the costs and benefits of germ-soma differentiation and the means of fitness reorganization.
(5) Several social genes (regA, glsA) underlying germ-soma separation and fitness reorganization have been identified.
(6) They have been studied in detail by cytologists, biochemists, developmental biologists, geneticists, and molecular biologists.
(7) Their distribution, natural history, and ecology has been extensively studied.
(8) They can easily be obtained from nature and maintained in the lab under realistic growing conditions that allow for an eco-physiological framework.
(9) The facultative sexual cycle is well characterized.
10) Perhaps most interesting is that, while representing a lineage of closely related species of increasing complexity, this diversification only went so far—the road to higher plants lay elsewhere.