Hossein Jorjani
First publication: 2026 – 06 – 30
In evolutionary genetics, the capacity of populations to adapt (their evolvability) is generally thought to depend on maintaining sufficient genetic variation. Too little variation may lead to rigidity and reduced adaptability, whereas excessive divergence may eventually weaken the coherence of the population and contribute to subdivision or speciation. Although the optimal balance depends on ecological and evolutionary circumstances, both excessive uniformity and excessive divergence may impose constraints on long-term persistence.
This line of reasoning may be extended to certain non-biological structures as well. In a democratic institution such as a parliament, it may likewise be prudent to maintain a balance between having too few and too many political parties. Too little political variation may result in rigidity, limited representational diversity, and reduced responsiveness to social change. Conversely, an excess of political fragmentation may weaken institutional coherence, impede effective decision-making, and divide the polity into smaller factions with diminished capacity to address shared challenges. A functional equilibrium between cohesion and diversification can contribute to institutional stability and adaptability.
Even from an evolutionary–ecological point of view, there is an inherent limit on the number of species that can coexist within a single niche. This constraint arises from fundamental principles of resource availability, competitive interactions, and the structural boundaries that define each ecological niche. The optimum number of species that a habitat can support naturally depends on the foraging range and spatial requirements of the organisms involved. Species with very small foraging ranges—such as many beetles and other insects—can coexist in far larger numbers within the same geographical area. By contrast, for larger vertebrates, especially carnivores, the energetic demands and territorial ranges required for stable populations sharply restrict the number of species that can be sustained. Thus, in many broad habitats the average number of large predatory species tends to fall in the range of roughly five to seven, reflecting the ecological balance between diversity and coherence.
At first sight, even quantum mechanics exhibits a superficially comparable pattern of limited coexistence appears even at the level of quantum particles. In quantum mechanics, fermions—such as electrons, protons, and neutrons—are subject to the Pauli Exclusion Principle, which states that no two identical fermions may occupy the same quantum state simultaneously. This rule imposes an absolute upper bound on the number of particles that can exist within any particular configuration, forcing additional fermions into higher energy states once the lower ones are filled. The resulting structure underlies the stability and stratification of matter, from atomic electron shells to the degeneracy pressure that sustains white dwarfs and neutron stars. Thus, comparable to ecological niches that can support only a limited number of species, quantum systems can support only a limited number of fermions in any given state, illustrating a deep and recurring pattern in nature: stable systems require constraints on occupancy, whether biological, ecological, or fundamental.
The Pauli Exclusion Principle also shapes the layered architecture of atoms by limiting the number of electrons that can occupy specific quantum states. As the principal quantum number n increases, the number of available orbitals—and thus the number of permissible electron states—expands rapidly, allowing progressively more complex atoms to exist. When n is small, as in the first two shells, only a few quantum states are available, and therefore only a limited number of elements can be constructed from such constrained configurations. By contrast, when n reaches the sixth or seventh shell, the number of orbitals becomes large, and the resulting atoms require intricate arrangements of electrons whose stability depends sensitively on subtle quantum interactions. Consequently, elements with electrons occupying the highest shells (n = 6-7 ) tend to be increasingly unstable, with many existing only in synthetic or short-lived forms, illustrating how the exclusion principle not only structures atomic architecture but also constrains the ultimate stability of matter.
Although the mechanisms governing these systems differ fundamentally, they all appear to confront a broadly similar structural problem: how to preserve sufficient diversity for adaptation or flexibility while maintaining enough coherence for stable organization. Whether this recurring pattern reflects a deeper organizing principle or merely analogous solutions to comparable structural problems remains an open question. At the very least, it suggests that durable systems—whether biological, ecological, institutional, or physical—often depend on balancing the generation of variation with the preservation of functional order.
Hossein Jorjani 