A plant evolutionary biologist has now reviewed the history of multicellularity and the changes that cells must have had to go through - like aspects of their shape, function, structure, and development - in order to be able to functionally combine with other cells.
Karl Niklas (Cornell University, Ithaca, NY), said that the curtail point is that the evolution of multicellular organisms occurred multiple times and involved different developmental 'motifs,' like chemistry of the 'glues' that allow cells to stick together.
However, there are certain sets of requirements that must be met in order for multicellularity to evolve. These include that cells must adhere to, communicate with, and cooperate with each other, and that cells must specialize in their functions.
In order to make these things happen, cells must not reject each other. In other words, they must be genetically compatible to some extent - analogous to how our human bodies reject foreign items that are not recognized by our cells. This first step is termed "alignment-of-fitness."
Interestingly, this "alignment-of-fitness" requires a "bottleneck" or unicellular stage when the organism consists of just one cell-a spore, zygote, or uninucleate asexual propagule.
The "export-of-fitness" stage is the second step necessary to the evolutionary process of multicellularity. This requires that cells work together for a common goal of reproducing more cohesive units, or individuals, like themselves and thereby work in a concerted way toward increasing their fitness. Once this is achieved, a distinct phenotype, or form, of organism exists.
The research has been published in the American Journal of Botany.