THE DEVELOPMENTAL ROLE OF THE EXTRACELLULAR MATRIX SUGGESTS A MONOPHYLETIC ORIGIN OF THE KINGDOM ANIMALIA.

The fundamental events of early development are similar in all animals, including sponges. Recent developments in the molecular biology of the extracellular matrix strongly suggest that the molecular mechanisms behind these events are also similar among all animals. I propose that the complex (collagen, proteoglycan, adhesive glycoprotein, and integrin) system that mediates cell motility and transitions between epithelial and motile cell types is central to multicellularity in animals. I further propose that the extracellular matrix is a deep rooted homology that unites the kingdom Animalia into a monophyletic group of multicellular organisms. © 1993 The Society for the Study of Evolution.