Last update: December 19, 2025

Lynn Margulis (1938-2011): Symbiosis as the Engine of Evolution

A Biologist Breaking with Classical Neodarwinism

Lynn Margulis (1938-2011) was an American biologist whose work profoundly changed the understanding of evolutionary mechanisms. At a time when the neo-Darwinian synthesis favored random mutation and natural selection as almost exclusive drivers of biological innovation, she proposed an alternative vision based on symbiosis.

Her central idea is that major evolutionary transitions, particularly the emergence of eukaryotic cells, do not result solely from gradual accumulations of mutations, but from cooperative integration events between distinct organisms.

The Modern Endosymbiotic Theory

Lynn Margulis' major contribution is the formalization and experimental support of the endosymbiotic theory. According to this theory, mitochondria and chloroplasts derive from free-living bacteria that were internalized by a primitive host cell.

The arguments put forward are based on well-established facts today:

Presence of circular DNA specific to mitochondria and chloroplasts
Double membrane compatible with a phagocytosis mechanism
Binary fission division analogous to that of bacteria
Phylogenetic similarities with α-proteobacteria and cyanobacteria

These observations indicate that the eukaryotic cell is a composite system, resulting from a stable fusion rather than simple internal complexification.

A Systemic and Thermodynamic Approach to Life

Lynn Margulis considered living organisms as open systems, far from thermodynamic equilibrium, capable of maintaining their organization through flows of energy and matter. In this context, symbiosis appears as an energy optimization mechanism.

The integration of a metabolically efficient symbiote, such as a respiratory bacterium, allows a significant increase in energy yield, an essential condition for the emergence of complex structures. The metabolic power of mitochondria can be linked to an increase in energy dissipation capacity, in accordance with the principles of non-equilibrium thermodynamics.

Consequences for the Notion of Biological Individual

Lynn Margulis' work leads to redefining the biological individual not as an isolated entity, but as a holobiont. The organism then becomes an integrated community of cooperating genomes.

This vision challenges a strictly competitive interpretation of evolution and introduces cooperation as a structuring factor on a large scale, without denying the role of natural selection.

Comparative Table: Evolutionary Mechanisms

Comparison of evolutionary mechanisms according to the neodarwinian and symbiotic approaches
Aspect	Classical Neodarwinism	Lynn Margulis' Approach	References
Main Driver	Random mutation and selection	Symbiosis and biological integration	Margulis, 1967
Origin of Eukaryotes	Gradual complexification	Fusion of prokaryotic lineages	Margulis, Sagan, 1986
Role of Cooperation	Secondary	Fundamental	Margulis, 1998
Vision of the Individual	Autonomous entity	Integrated symbiotic system	Gilbert et al., 2012

A Lasting Scientific Legacy

Long marginalized, Lynn Margulis' ideas are now widely integrated into modern biology, particularly in microbiology, ecology, and the study of the microbiome. They have paved the way for a more collective, physical, and systemic understanding of life.

Her legacy reminds us that evolution is not only a process of selection among competitors, but also a story of lasting alliances between forms of life.