Growth Transcends Categories

Your cells already know about modes. 

A cell rarely does just one thing for its entire life. Almost every cell goes through seasons. It goes through phases where one function is supremely important, and then its environment changes and its role changes. It enters an entirely different phase. 

There are two main modes that many of your cells occupy at some point in their lifetimes. The cell’s functions change entirely when it shifts between them. They two modes are epithelial – a mode for normal life – and mesenchymal – a mode for times of massive change. 

Epithelial cells are sticky and deeply oriented. They find their bearings by sensing their neighbors, they position themselves in one particular way, and then they sink in and hold on. They’re in it for the long haul, persistent in accomplishing their tasks, tough to dislodge and resistant to change. 

Mesenchymal cells are full of potential and lacking in specificity. They’re precursors, beginnings and starting points. Mesenchymal cells have the ability to differentiate – to develop – into just about any type of cell. But on their own, they’re not really able to get any particular job done. 

There’s one type of tissue whose cells are classified as both epithelial and mesenchymal. These are the cells that are neither and both at the same time, the ones that fit in no categories and transcend any attempt at definition.

Biology can be seen as an attempt to draw boxes around the diverse and multifaceted forms of life, but every once in a while there’s a living thing that insists on squirming out of that box, sprouting up until it pushes away that tightly fitted lid and showing us how foolish we were to ever think we could name, define and contain a mystery as wild as LIFE.

These cells, the ones that fall into both categories at the same time, are exactly those squirmy, surprising and defiant living things. 

What is this wild and mysterious tissue whose cells are both epithelial and mesenchymal? Developing tissue. These are cells that are neither precursors nor finished products. They’re somewhere in the middle. When we try to apply our definitions, they fit nowhere. Growth and development are marked by transcendence of categories.