Waddington landscape, bistability, and irreversible fate decisions
Conrad Waddington's 1957 "epigenetic landscape" metaphor captures cell fate commitment as a ball rolling down a branching valley: early cells sit at a ridge (pluripotent), and progressively roll into one of several attractor valleys (committed fates), making increasingly irreversible decisions. This corresponds to a bistable dynamical system with mutual inhibition: two transcription factors (e.g., GATA1 vs PU.1) each repress the other, creating two stable states and one unstable equilibrium. Noise from stochastic gene expression perturbs cells across the ridge, with bias from instructive signals (morphogens, cytokines) tilting the landscape. Once committed, epigenetic silencing via H3K27me3 raises the barrier, making reversal energetically impossible without reprogramming factors (Yamanaka, 2006).