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.
How exactly steps such as cell-to-cell adhesion or communication were achieved in plants, animals, fungi, and algae differs among the major eukaryotic clades, yet an important aspect is that these multicellular organisms all went through a similar series of steps on their way to becoming multicellular, functional organisms.
As Niklas puts it: "This convergent evolution is well summarized by the saying 'There are many roads to Rome, but Rome is not what it used to be'."
In fact, these stages can be mapped on to theoretically possible body plans, illustrating the most plausible series of evolutionary stepsunicellular to colonial to multicellularthat is seen in algae, land plants, and animals. Niklas also posits a plausible alternate evolutionary route, starting with a single cell containing multiple nuclei (e.g., from a siphonous to multicellular form) and finds support for this in the observed forms of some fungi and algae.
"This review of the literature has now brought my attention to 'cooperation'" concludes Niklas, "because multicellularity requires cells to work together. Cheating cells cannot be tolerated over the long run because like a cancer they can gain the upper hand and kill a multicellular organism."
|Contact: Richard Hund|
American Journal of Botany