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Epigenetic landscape
Waddington’s epigenetic landscape is a metaphor for how gene regulation modulates development.[10] Among other metaphors, Waddington asks us to imagine a number of marbles rolling down a hill.[11] The marbles will compete for the grooves on the slope, and come to rest at the lowest points. These points represent the eventual cell fates, that is, tissue types. Waddington coined the term chreode to represent this cellular developmental process. This idea was actually based on experiment: Waddington found that one effect of mutation (which could modulate the epigenetic landscape) was to affect how cells differentiated. He also showed how mutation could affect the landscape and used this metaphor in his discussions on evolution—he was the first person to emphasise that evolution mainly occurred through mutations that affected developmental anatomy.
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