Cited by 160Complex Network Analysis TechniquesComplex Systems and DynamicsBioinformatics and Genomic Networks

The DOI matches its Crossref record; 76 of the 79 references it cites were found in a registry or an index, and 1 are not checked yet; none of the 48 sources its claims cite is checked for support yet.

On the origins of hierarchy in complex networks

Open access
Corominas-Murtra, Bernat, Goñi, Joaquín, Solé, Ricard V., Rodríguez-Caso, Carlos·2013·Proceedings of the National Academy of Sciences

Abstract

Hierarchy seems to pervade complexity in both living and artificial systems. Despite its relevance, no general theory that captures all features of hierarchy and its origins has been proposed yet. Here we present a formal approach resulting from the convergence of theoretical morphology and network theory that allows constructing a 3D morphospace of hierarchies and hence comparing the hierarchical organization of ecological, cellular, technological, and social networks. Embedded within large voids in the morphospace of all possible hierarchies, four major groups are identified. Two of them match the expected from random networks with similar connectivity, thus suggesting that nonadaptive factors are at work. Ecological and gene networks define the other two, indicating that their topological order is the result of functional constraints. These results are consistent with an exploration of the morphospace, using in silico evolved networks.

Checked 2026-10-07 · 1 reference not checked yet

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

The paper defines a 3D morphospace of hierarchy using treeness, feedforwardness, and orderability, then maps 125 real networks and null models into it. It finds four major clusters, with two matching random-network expectations and two—ecological and gene networks—apparently shaped by functional constraints.

Key findings

  • The morphospace Ω is defined by coordinates \(u(G)=(T,F,O)\), with perfect hierarchy at \((1,1,1)\) and a totally cyclic network at \((0,0,0)\); random homogeneous and broad networks occupy basically the same region, within the bow-tie plane \(T(G)=0\).
  • Among 125 real networks across 13 classes, most fall into four clusters: metabolic, neural, linguistic, and some social networks lie in the lower bow-tie domain within the random-graph cloud; electronic circuits and software graphs form a feedforward band with \(-0.2<T(G)<0.2\); gene regulatory networks plus a kinase network show slightly positive \(T(G)\) and high \(O\); ecological flow graphs cluster around \(u(G)=(0.35,0.45,0.25)\).
  • Isolated extremes include a cell lineage at \(u(G)=(0.95,1,1)\) and a small social network at \(u(G)=(-1,0.06,0.09)\).
  • In silico evolution over 300 target points, three \(O\) values \(\{0.15,0.5,0.85\}\), and \(10^3\) generations showed some regions are accessible while others are inaccessible, suggesting non-adaptive processes may play a major role in shaping hierarchies.

Methods

  • Directed graphs are condensed by collapsing strongly connected components into a node-weighted condensed graph \(G_C\); hierarchy is quantified by treeness \(T\) from forward/backward entropies over DAGs and leaf-removal subgraphs, feedforwardness \(F\) from path weights of cyclic modules, and orderability \(O\) as the fraction of nodes not in any cycle.
  • The study analyzes 125 real networks from 13 classes and compares them with directed Erdős–Rényi, Barabási–Albert, and Callaway model ensembles; randomization uses two methods preserving either the undirected degree sequence and component structure or the directed degree sequence and component structure, with 100 replicas per network and \(4|E|\) link switches or \(20|E|\) trials.
  • An evolutionary search starts from small random graphs and selects graphs minimizing Euclidean distance to target points in Ω via random link addition and deletion, with 250 replicas per target point and up to 1000 generations.

Limitations

  • The paper states that the study uses a static view dominated by causal relations and does not include functionality, dynamics, or weighted structures; these are left for further work.
  • The paper notes that the evolutionary algorithm’s parameters may shape the observed fitness landscape, that the experiment has high computational cost, and that small network sizes provide only a coarse-grained picture of reachability.
  • The formalism assumes connected directed graphs; the Appendix states that unconnected components have no causal relation and that hierarchy loses meaning across them. Exact analytical estimates are not derived for \(F\), and the \(T\) and \(O\) random-graph estimates rely on simplifying assumptions.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1073/pnas.1300832110

Cites

76 of 77 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Verification

Claims the paper makes

69 Own interpretation · 38 Own result · 27 Not checked yet · 13 No basis given · 7 Own method

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Show all 87 claims

  • It may state two separate claims as one. 31
  • Probably not a substantial claim. 44
  • The quote only partly states this claim. 3
67 of 67
  • The paper relies on this without support.

    No general theory that captures all features of hierarchy and its origins has been proposed yet.

    “Despite its relevance, no general theory that captures all features of hierarchy and its origins has been proposed yet.”
  • The paper relies on this without support.

    Null models do not consider optimal designs or functional constraints.

    “Since null models do not consider optimal designs or functional constraints, they provide good insights about the part of the morphospace where no selection pressure is at work.”
  • The paper relies on this without support.

    The region occupied by null models indicates where no selection pressure is at work.

    “Since null models do not consider optimal designs or functional constraints, they provide good insights about the part of the morphospace where no selection pressure is at work.”
  • The paper relies on this without support.

    In general, neither biological nor technological webs match the feedforward pattern.

    “But, in general, neither biological nor technological webs match the feedforward pattern.”
  • The paper relies on this without support.

    The 125 real networks used are representative of natural and artificial systems.

    “Here we use N n = 125 real networks encompassing 13 classes of natural and artificial systems”
  • The authors state this as an assumption.

    Unconnected components have no causal relation of any kind, and therefore the concept of hierarchy loses any meaning for them.

    “we assume that unconnected components have no causal relation of any kind and, therefore, the concept of hierarchy looses any meaning.”
  • The authors state this as an assumption.

    A perfectly hierarchical system has the properties of order, reversibility, and pyramidal structure.

    “The perfectly hierarchical system will have the following three properties: - order , - reversibility and - pyramidal structure .”
  • The paper relies on this without support.

    Links in a directed graph describe some kind of causal relation between two elements of the set which is considered relevant for the system.

    “In any directed graph, links describe some kind of causal relation between two elements of the set which is considered relevant for the system.”
  • The paper relies on this without support.

    Rigorous and systematic confrontation of real data with their randomized counterparts elucidates much of the possible origins of the observed patterns.

    “It is important to stress that the rigorous and systematic confrontation of real data with their randomized counterparts elucidates much of the possible origins of the observed patterns.”
  • The authors state this as an assumption.

    The ensemble G_C(G) is well behaved, meaning that the averages collapse to the most probable value of a given observable.

    “The first one concerns the assumption that the ensemble G C ( G ) is well behaved , which means that the averages collapse to the most probable value of a given observable.”
  • The authors state this as an assumption.

    Small SCCs that can also be present within the graph represent a negligible fraction of it when compared to the size of the GSCC.

    “if we assume that small SCC s that can be also present within the graph represent a negligible fraction of it when compared to the size of the GSCC”
  • The authors state this as an assumption.

    There is no correlation between in-degree and out-degree, p(k_in, k_out) approximately equals p(k_in)p(k_out).

    “Following [16], we know that, if there is no correlation between in and out -degrees p ( k in , k out ) ≈ p ( k in ) p ( k out ), we can estimate the size of the GSCC as:”
12 of 12

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

3 of 3

Citations

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Metadata

Authors
Corominas-Murtra, B., Goñi, J., Solé, R. V., & Rodríguez-Caso, C.
Affiliations
  • Institució Catalana per a la Recerca i Estudis Avancats–Complex Systems Laboratory, Universitat Pompeu Fabra, 08003 Barcelona, Spain;
  • Indiana University Bloomington (US)
  • Institució Catalana de Recerca i Estudis Avançats (ES)
Venue
Proceedings of the National Academy of Sciences
Published
2013-07-29
Volume
110
Issue
33
Pages
13316-13321
ISSN
  • 0027-8424 (ISSN-L)
  • 1091-6490
OpenAlex
W2141141714
Cited by
160
References
79
Citations by year
2026: 7 · 2025: 10 · 2024: 9 · 2023: 13 · 2022: 12 · 2021: 15 · 2020: 12 · 2019: 12 · 2018: 13 · 2017: 12 · 2016: 23 · 2015: 10 · 2014: 9 · 2013: 3
FWCI
10.67
Type
journal article
Language
en
Open access
Locations
  • Proceedings of the National Academy of Sciences (publishedVersion)
  • arXiv (Cornell University) (publishedVersion)
  • Europe PMC (PubMed Central) (publishedVersion)
  • PubMed Central (publishedVersion)
  • PubMed (publishedVersion)
  • DIGITAL.CSIC (Spanish National Research Council (CSIC)) (submittedVersion)
  • arXiv (Cornell University)
Topics
  • Physical Sciences › Physics and Astronomy › Statistical and Nonlinear Physics › Complex Network Analysis Techniques
  • Physical Sciences › Physics and Astronomy › Statistical and Nonlinear Physics › Complex Systems and Dynamics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Bioinformatics and Genomic Networks
Keywords
network hierarchy, complex networks, morphospace, theoretical morphology, network topology, ecological networks, gene regulatory networks, social networks, technological networks, random networks, functional constraints
MeSH terms
Cell Physiological Phenomena, Biological Evolution, Models, Theoretical, Social Support, Ecosystem, Gene Regulatory Networks

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