A negative feedback loop occurs when the output of a process inhibits or reverses that process, reducing the original change. It stabilizes a system by counteracting deviations and moving the system back toward equilibrium.
This is a core SL and HL concept in IB ESS Subtopic 1.2, Systems. The mechanism works in four stages:
- A disturbance moves a system away from its equilibrium.
- The system detects or responds to that change.
- The response acts in the opposite direction to the disturbance.
- The original change is reduced, helping restore stability.
For example, consider a deer population near its carrying capacity, the maximum population size supported by available resources. If the population increases, competition for food intensifies. Mortality may rise and reproduction may fall, causing the population to decrease toward carrying capacity again.
| Change in the system | Stabilizing response |
|---|---|
| Population rises above carrying capacity | Competition increases, reducing population growth |
| Population falls below carrying capacity | More resources per individual may increase survival and reproduction |
| Room temperature rises above a thermostat setting | Heating switches off |
Negative feedback commonly maintains a stable equilibrium, in which the system fluctuates around an average condition. In an open ecosystem, continuous inputs and outputs mean conditions are rarely completely constant; instead, feedback limits the size of fluctuations and increases resilience.
A common misconception is that “negative” means environmentally harmful. It does not. Negative describes the direction of the feedback: it opposes change. By contrast, positive feedback amplifies a disturbance and may drive a system toward a tipping point.
Exam technique: For an “explain” question, identify the initial disturbance, show how the response opposes it, and link this explicitly to equilibrium or stability. In a systems diagram, use arrows to show the causal sequence and label whether each relationship increases or decreases the next variable.