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The conventional wisdom on negative feedback in biology is that it
checks spontaneous fluctuations and provides homeostasis to external
changes. We challenge this view by showing how different sources of
variation - spontaneous low-copy fluctuations, feedback noise, and
external changes - are suppressed according to incompatible principles,
generating frustration trade-offs where reducing one type of variation
amplifies another. The trade-offs produce physical limits to noise
suppression that can be formulated in terms of the biological
constraints. We further show how approaching the limits can require
exotic features that have been widely overlooked in biology, including
counteracting feedback loops, accelerating gains, and non-Markovian
molecular memory.
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