At the KLI, I intend to develop a theory for the developmental-evolutionary concept of “tissue type” which will serve as the core conceptual thread linking the chapters of my final dissertation manuscript, and write this as a framework paper. Main Driving questions include how quasi-autonomous tissue identity originates and is maintained in evolution, how cell-cell interactions give rise to the emergent properties of tissues, how tissue microenvironment and cellular niche construction drive tissue identity and homeostasis, and how tissue type innovation occurs vis-à-vis cell type innovation.