OK, it may be informative with the following highlights from the article:
A. “Multicellular organisms typically develop in one of two ways, either through division without cell separation or through cell aggregation. The first mode of multicellular development is exemplified by organisms like plants, animals and fungi while the second mode, a less common strategy among eukaryotes, is nicely illustrated by the dictyostelid slime molds.”
B: “Many of the multicellular lineages present on earth today evolved from unicellular ancestors with rigid cell walls [like] land plants, fungi, and red and brown algae […]. For these cells, adhesion is a passive process very different from the intimate cellular associations found in animals and Dictyostelids; physical connections are established as new cells form and the resulting attachments between cells are stabilized and maintained throughout life. This type of multicellular development, in which cells divide and remain linked by their shared cell wall, has important implications for the developing organism as the cells cannot reposition themselves after cytokinesis.”
C: " animal cells lack cell walls, permitting them to adhere dynamically and reorganize into complex tissues and organs during development. In contrast, […] a cell wall […] provides structural integrity but prohibits cell rearrangement."
So, in summary, there are two main pathways (A) for achieving multicellularity:
- Division without cell separation (plants, fungi & animals)
- Aggregration of formerly disassociated cells (dictyostelid slime molds)
And there are two modes (B) of multicellularity:
- cell wall linkage (algae, plants & fungi)
- collagenous matrix embedment (animals)
The aggregative pathway (A1) is highly transitional and it’s hard to see how to arrive at an integral multicellular that way. The cell wall linkage mode (B1) is much more limiting and rigid and clearly only has yielded passive life forms.
So to boil it down for to something very simple in-game, it would make sense to stick to these phases:
MICROBE STAGE
- Prokaryotic phase Simple prokaryote-like cell
- Eukaryotic phase With the acquisition of nucleus
- Aggregative phase Like A1 and with the acquisition of “binding factors”
- Multicellular phase Like B2 and with the acquisition of “junction factors”
The latter phase will then set things up for the transition to the MULTICELLULAR STAGE.