In other words, is there any individual cell that can decide between two or more options, or all they all solely chemical and mechanical reactions without any self-determination at all?
There are good answers about differentiation from stem cells, process governed by the evolutionary determined genetic information stored within the cell itself. This genetic information was/is influenced by environment but that influence tends to be slow and subtle.
I have another answer to contribute. Metastatic cancer cells. These are cells which detach from primary tumors in any part of the body, then have to break into the lymph or blood and then they in a sense “decide” where they want to settle. We now know they’ll have preferences: some cancers will metastase to liver, some to lung, some to brain; but before they do so, these cells will literally circle around the body, searching for a “perfect spot”. Once they find it, they settle, often entirely changing their O.G. tumorous behaviour in the process which in return makes them super unpredictable and hard to kill. And all it takes is one wandering cell.
