Degeneracy: Why Can Different Structures Perform Similar Functions?

Degeneracy means that structurally different parts can perform a similar function under some conditions while retaining distinct roles under others. It does not mean deterioration, nor is it simply two identical spare parts.

Imagine two routes to a city hospital: one crosses a railway line, while the other passes through residential streets. On an ordinary day, both reach the same destination. In heavy rain or peak traffic, however, they behave differently. Producing the same result has not erased their structural differences; those differences preserve room to adjust.

Degeneracy is close to redundancy, but redundancy stresses like-for-like backup, whereas degeneracy involves heterogeneous parts whose functions overlap only in limited contexts. It also differs from multifunctionality: one part serving several purposes is not the same as several unlike parts converging on a similar result. Reliability does not always come from copying. Sometimes difference itself is what keeps a system workable.

https://www.pnas.org/doi/10.1073/pnas.231499798