Lynn Margulis

1.1 The Orthodoxy of the Modern Synthesis

In the mid-twentieth century, evolutionary biology was consolidated under the Modern Synthesis (Neo-Darwinian theory). Developed between 1930 and 1950 by synthesizing Mendelian genetics, Darwinian selection, and mathematical population genetics (Ronald Fisher, J.B.S. Haldane, Sewall Wright), and codified by Ernst Mayr and Theodosius Dobzhansky, the paradigm rested on four axioms: 1. Gradualism: Evolution proceeds exclusively by accumulating small, discrete variations (point mutations and allelic recombinations). 2. Exclusivity of Natural Selection: Natural selection acting on differential reproductive success among individual organisms is the sole organizing force of adaptive evolution. 3. Strict Vertical Inheritance: Genetic inheritance is strictly genealogical. Phylogeny is an uncrossable, bifurcating tree ($A \to B$ and $C$) where branches never rejoin. 4. Zoocentric Bias: Conceptual models were calibrated against sexually reproducing diploid macro-organisms (animals and flowering plants). Microorganisms were treated as primitive oddities outside the core evolutionary engine.

1.2 Historical Precursors: The Discarded Heresies

Composite cellular models had surfaced earlier, but lacked biochemical mechanisms and were dismissed as fringe speculation: * Andreas Schimper (1883): Observed that chloroplasts (Chlorophyllkörner) divide autonomously and suggested green plants arose from the union of a colorless organism and a chlorophyll-bearing microbe. * Konstantin Mereschkowski (1905, 1910): Coined symbiogenesis (symbiogenez), proposing that plant cells arose through the combination of an amoeboid host and photosynthetic cyanobacteria. His dismissal was sealed by his rejection of Mendelian genetics. * Boris Kozo-Polyansky (1924): Published A New Principle of Biology, seeking to reconcile symbiogenesis with Darwinian selection; his Russian text was unread in the West. * Ivan Wallin (1927): Published Symbionticism and the Origin of Species, arguing mitochondria were bacterial endosymbionts. Wallin claimed to cultivate isolated mitochondria in vitro—an unreplicable finding that discredited symbiotic hypotheses for decades.

1.3 Lynn Sagan (Margulis) and "On the Origin of Mitosing Cells" (1967)

In 1965–1966, while at Boston University, Lynn Margulis (publishing under her married name, Lynn Sagan) synthesized emerging cytological, biochemical, and electron-microscopy data into Serial Endosymbiotic Theory (SET).

The manuscript was rejected by approximately fifteen journals (frequently dismissed as ungrounded storytelling) before being accepted by James F. Danielli in the Journal of Theoretical Biology:

Sagan, Lynn (1967). "On the Origin of Mitosing Cells." Journal of Theoretical Biology, 14(3), 225–274.

The paper made three testable assertions: 1. Mitochondria: Originated as aerobic eubacteria engulfed by an anaerobic host during the oxygenation crisis. 2. Plastids: Originated in a subsequent endosymbiosis where a mitochondriate eukaryote engulfed a photosynthetic cyanobacterium. 3. Undulipodia (Cilia/Flagella): Originated from ectosymbiotic spirochetes attached to the host surface.

Margulis expanded this framework in two monographs: Origin of Eukaryotic Cells (1970) and Symbiosis in Cell Evolution (1981).

========================================================================================
                          SERIAL ENDOSYMBIOTIC THEORY (SET)
========================================================================================

 [Anaerobic Host Cell]   +   [Aerobic Bacterium] 
 (Methanogenic/Asgard)       (Alphaproteobacterium)
           │                           │
           └─────────────┬─────────────┘
                         ▼
             [Primary Endosymbiosis I]
                         │
                         ▼
            [Ancestral Aerobic Eukaryote]   +   [Cyanobacterium]
            (Mitochondriate Protist)            (Photosynthetic)
                         │                             │
                         └──────────────┬──────────────┘
                                        ▼
                            [Primary Endosymbiosis II]
                                        │
                                        ▼
                             [Photosynthetic Eukaryote]
                             (Ancestral Alga / Green Plant)
========================================================================================

The vindication of SET was driven by unambiguous cytological, pharmacological, and phylogenomic proofs.

2.1 Extranuclear Genomic Architecture

Mitochondria and chloroplasts maintain dedicated, semi-autonomous genetic hardware: * Topology: Organellar DNA (mtDNA and cpDNA) exists as covalently closed circular, double-stranded molecules devoid of eukaryotic histone spools, mirroring bacterial nucleoids. * Replication Kinetics: Replicates semi-conservatively via displacement loops (D-loops) using dedicated DNA polymerases ($\text{Pol }\gamma$, homologous to bacterial family-A polymerases). Replication occurs continuously, uncoupled from nuclear S-phase mitosis. * Irreversible Loss: If organelles are purged (e.g., ethidium bromide treatment), the cell cannot regenerate them de novo; they arise strictly from the binary fission of pre-existing organelles.

2.2 Translation Machinery and Pharmacological Profiles

Organellar protein synthesis displays prokaryotic biochemistry, distinct from the surrounding cytoplasm:

Antibiotics targeting bacterial ribosomes arrest organellar protein synthesis while sparing host cytosolic translation; cycloheximide halts cytosolic translation while sparing organelles.

2.3 Membrane Ultrastructure and Diagnostic Lipids

The double-membrane boundary preserves the anatomical scar of engulfment: 1. Membrane Division: The inner membrane represents the ancestral bacterial plasma membrane ($>75\%$ protein by mass), housing the electron transport chain and $F_0F_1$-ATP synthase. The outer membrane derives from the host phagosome, modified with bacterial porins. 2. Cardiolipin: The inner mitochondrial membrane is enriched ($20\%$ of phospholipids) with cardiolipin ($1,3\text{-bis}(sn\text{-}3'\text{-phosphatidyl})\text{-}sn\text{-glycerol}$), a signature lipid absent from eukaryotic plasma membranes and found elsewhere almost exclusively in Gram-negative eubacteria. 3. Porins: Outer mitochondrial and chloroplast membranes contain transmembrane $\beta$-barrel proteins (porins/VDAC), structural features unique to the outer envelopes of Gram-negative bacteria.

========================================================================================
                      MITOCHONDRIAL MEMBRANE ULTRASTRUCTURE
========================================================================================

          Eukaryotic Cytosol (Host Environment)
   ─────────────────────────────────────────────────────── Outer Membrane
       Porins (β-barrels, bacterial envelope origin)      (Phagosomal / Outer)
   ┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈ Intermembrane Space
       Proton ($H^+$) Reservoir ($\Delta\text{pH} + \Delta\Psi$)
   ─────────────────────────────────────────────────────── Inner Membrane
       Cardiolipin-Rich Bilayer (Bacterial Plasma Origin)
       Respiratory Chain Complexes (I, II, III, IV) & $F_0F_1$-ATP Synthase
   ┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈ Matrix (Bacterial Cytosol)
       Circular mtDNA, 70S/55S Ribosomes, Krebs Cycle Enzymes
========================================================================================

2.4 Phylogenomic Confirmation (Woese, Gray, Doolittle)

Definitive proof arrived via ribosomal RNA sequencing: * Carl Woese (1977) established that $16\text{S}$ rRNA acts as an evolutionary chronometer across deep time. * Michael W. Gray and W. Ford Doolittle (1982) demonstrated that chloroplast $16\text{S}$ rRNA clusters directly within Cyanobacteria ($>80\%$ identity with Synechococcus), while mitochondrial rRNA branches squarely inside the Alphaproteobacteria, closest to the Rickettsiales (obligate intracellular endosymbionts sharing homologous respiratory chains and ADP/ATP translocases). * The eukaryotic genome is a phylogenetic chimera: an archaeal-derived host containing alphaproteobacterial and cyanobacterial genomes.

3.1 The Eocyte Hypothesis and Asgard Archaea

For thirty years, host identity was contested: * The Archezoa Hypothesis (Cavalier-Smith, 1987): Proposed that early eukaryotes (Archezoa, e.g., Giardia, Trichomonas) branched off before acquiring mitochondria. By the late 1990s, this was disproven: all known "amitochondriates" possess derived relict organelles (mitosomes or hydrogenosomes) and nuclear genes of alphaproteobacterial origin. Mitochondria are ancestral to all living eukaryotes. * The Asgard Archaea Discovery (2015–2020): Metagenomic discovery of the Asgard superphylum (Lokiarchaeota, Thorarchaeota, Heimdallarchaeota) confirmed James Lake’s 1988 Eocyte hypothesis: eukaryotes branch directly from within Archaea. Asgard genomes encode eukaryotic signature proteins (ESPs)—actin, profilin, ubiquitin systems, Rab-like GTPases, and ESCRT membrane-remodeling complexes.

========================================================================================
               THE TWO-DOMAIN TREE OF LIFE (EOCYTE / ASGARD TOPOLOGY)
========================================================================================

  BACTERIA                                    ARCHAEA
     │                                           │
     ├── Cyanobacteria ──(Plastid)───┐           ├── Euryarchaeota
     │                               │           ├── TACK Superphylum
     └── Alphaproteobacteria         │           └── Asgard Archaea (Lokiarchaeota)
              │                      │                          │
              └──(Mitochondrion)──┐  │                          ▼
                                  ▼  ▼                  ┌───────────────┐
                                ┌───────────────────────┤ EUKARYA (HOST)│
                                │   Genomic Chimera     └───────────────┘
                                └───────────────────────────────────────┘
========================================================================================

3.2 Syntrophy: The Hydrogen Hypothesis

William Martin and Miklós Müller (1998) resolved the initial selective driver via the Hydrogen Hypothesis: 1. Host: An anaerobic, autotrophic archaeon dependent on molecular hydrogen ($H_2$) and carbon dioxide ($CO_2$) for methanogenesis: $$\text{CO}_2 + 4\text{H}_2 \longrightarrow \text{CH}_4 + 2\text{H}_2\text{O}$$ 2. Symbiont: A facultatively anaerobic alphaproteobacterium fermenting organic substrates in anoxia and releasing $H_2$ and $CO_2$ as metabolic waste. 3. Selective Entrainment: The host closely associated with the symbiont to harvest waste $H_2$. When oxygen flooded the biosphere during the Great Oxidation Event (GOE) (~2.4–2.1 Ga), the symbiont utilized cytochrome $c$ oxidase to detoxify oxygen and generate immense ATP yields: $$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 + 32\text{ADP} + 32\text{P}_i \longrightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + 32\text{ATP}$$

3.3 The Bioenergetic Expansion of Complexity (Lane & Martin)

Nick Lane and William Martin (2010) resolved why morphological complexity evolved only in eukaryotes: * The Prokaryotic Surface-Area Bottleneck: Bacteria drive ATP synthesis across their external plasma membrane. As cell volume scales ($V \propto r^3$), surface area lags ($A \propto r^2$). Scaling up prokaryotic cell size requires duplicating the entire genome at the cell periphery to run local bioenergetics, keeping energy available per gene virtually flat: $$\text{Energy per gene (Prokaryote)} \approx 10^{-14} \text{ W / gene}$$ * Internalized Bioenergetics: By packing thousands of energy-transducing bacterial symbionts inside the cell, eukaryotes expanded internal respiratory membrane surface area up to $100,000$-fold without increasing outer cell surface area. * Asymmetric Genome Downsizing: The symbiont transferred $>99\%$ of its genes to the central nucleus, retaining only minimal local genomes. The host maintains immense bioenergetic capacity at near-zero genetic maintenance cost: $$\text{Energy per gene (Eukaryote)} \approx 10^{-9}\text{--}10^{-10} \text{ W / gene} \quad (\sim 100,000\times \text{ surplus})$$ This bioenergetic surplus funded the costs of nuclear architecture, introns, alternative splicing, chromatin regulation, and massive multicellular development.

3.4 Endosymbiotic Gene Transfer (EGT) and the CoRR Hypothesis

Following the merger, Endosymbiotic Gene Transfer (EGT) transferred thousands of bacterial genes to the nuclear genome. Human mtDNA now retains only 37 genes (13 polypeptides, 22 tRNAs, 2 rRNAs), while $>1,200$ mitochondrial proteins are encoded in the nucleus and imported through TOM/TIM translocons.

The CoRR Hypothesis (Co-location for Redox Regulation): John F. Allen (1992, 2003) showed why organelles retain any DNA at all: * Retained organellar genes code for core hydrophobic electron transport proteins (Cytochrome $b$, Cytochrome $c$ oxidase subunits I–III, ATP synthase subunit 6). * Mismatched electron flow causes electrons to leak to oxygen, producing reactive oxygen species ($O_2^{\bullet-}$, $H_2O_2$, $^\bullet OH$), resulting in membrane lipid peroxidation and cell lysis. * Signaling the distant nucleus takes minutes to hours; local organellar genomes permit millisecond-scale transcriptional autoregulation responsive to local redox state, avoiding lethal electron leakage.

While Margulis's mitochondrial and plastid theories were canonized, her third claim—the symbiotic origin of cilia, flagella, and the mitotic apparatus—proved to be an untenable overreach.

4.1 The Spirochete Model and Mixotricha paradoxa

Margulis maintained that eukaryotic motility structures (which she termed undulipodia to distinguish them from prokaryotic flagella) arose from ectosymbiotic spirochetes (Treponema-like bacteria) attaching to the host cortex, evolving into basal bodies, and migrating inward to form the mitotic spindle.

Her living model was Mixotricha paradoxa, a gut symbiont of the termite Mastotermes darwiniensis. Light microscopy suggests Mixotricha swims via cilia, but electron microscopy revealed that $500,000$ surface-attached spirochetes coordinated by membrane brackets drive its movement, proving bacteria can serve as outsourced motility engines.

========================================================================================
            MARGULIS'S PROPOSED SPIROCHETE-TO-UNDULIPODIUM TRANSITION
========================================================================================

 [Free-Living Spirochete]  ──>  [Ectosymbiotic Attachment]  ──>  [Internalized Axoneme]
 (e.g., Treponema)               (e.g., Mixotricha surface)      ((9+2) Undulipodium)
                                                                           │
                                                                           ▼
                                                                  [Mitotic Spindle Aster]
                                                                  (Centrosome / Mitosis)
========================================================================================

4.2 Falsification and Modern Consensus

The spirochete origin was decisively falsified: 1. Absence of Basal Body DNA: Centrioles, kinetosomes, and basal bodies contain zero endogenous nucleic acid. Early reports of basal-body DNA were disproven as cytoplasmic RNA artifacts. 2. Tubulin vs. Flagellin: Bacterial flagella are formed of flagellin and driven by proton-motive rotary stators. Eukaryotic $(9+2)$ axonemes are composed of $\alpha$- and $\beta$-tubulin heterodimers powered by dynein ATPases. Tubulin is an evolutionary homolog of FtsZ, an ancestral archaeal/bacterial GTPase present across the Asgard Archaea (artubulin, cetZ), confirming host autogenous origin. 3. Genomic Incongruence: Spirochete genomes (Treponema, Borrelia) lack homologs to the axonemal dynein heavy chain, radial spokes, or intraflagellar transport (IFT) complexes.

Axonemes and mitosis evolved autogenously within the archaeal host line via diversification of ancestral cytoskeletal elements.

Between 1970 and 1980, Margulis collaborated with atmospheric chemist James Lovelock, developing the Gaia Hypothesis into a grounded ecological theory.

5.1 Atmospheric Disequilibrium

Lovelock discovered while designing planetary life-detection systems for NASA JPL that Earth's atmosphere is in persistent chemical disequilibrium: * Dead Planets (Mars, Venus): $>95\%\ \text{CO}_2$, trace nitrogen, virtually no oxygen or methane—thermodynamically spent equilibrium. * Earth (Living System): $21\%\ \text{O}_2$, $78\%\ \text{N}_2$, and $1.7\text{ ppm}\ \text{CH}_4$. Because oxygen and methane react rapidly, their steady coexistence requires life to continuously inject megatons of both gases annually.

========================================================================================
                          PLANETARY ATMOSPHERIC PROFILES
========================================================================================

  GAS COMPONENT         EARTH (LIVE)         MARS (DEAD)          VENUS (DEAD)
  ─────────────────────────────────────────────────────────────────────────────
  Carbon Dioxide (CO2)     0.04%                95.3%                96.5%
  Molecular Oxygen (O2)   20.95%                 0.13%               Trace
  Molecular Nitrogen (N2) 78.08%                 2.7%                 3.5%
  Methane (CH4)            1.7 ppm               0.00 ppm             0.00 ppm
  Thermodynamic State:   Extreme Disequilibrium  Complete Equilibrium Complete Equilibrium
========================================================================================

5.2 Margulis's Microbial Engines

Margulis anchored Lovelock's cybernetic models in microbial biogeochemistry: 1. The CLAW Hypothesis (Charlson, Lovelock, Andreae, Warren, 1987): Marine phytoplankton release dimethylsulfoniopropionate (DMSP), cleaved into volatile dimethyl sulfide (DMS). Atmospheric DMS oxidizes into sulfate aerosols, acting as cloud condensation nuclei (CCN). Increased cloud cover raises planetary albedo, cooling the oceans and regulating algal blooms. 2. Carbon-Silicate Weathering: Atmospheric $\text{CO}_2$ dissolved in rain forms carbonic acid ($\text{H}_2\text{CO}_3$), weathering continental silicate rocks: $$\text{CaSiO}_3 + 2\text{CO}_2 + \text{H}_2\text{O} \longrightarrow \text{Ca}^{2+} + 2\text{HCO}_3^- + \text{SiO}_2$$ Marine organisms precipitate $\text{CaCO}_3$ shells, sequestering carbon into limestone sediments. Soil microbes and mycorrhizae accelerate rock weathering by $10\text{--}100\times$, stabilizing global climate despite a $30\%$ increase in solar luminosity since the Archean (Faint Young Sun Paradox). 3. Oxygen Homeostasis: Sustained near $21\%$—below the $25\%$ spontaneous combustion threshold for terrestrial flora and above the $15\%$ hypoxic threshold for respiratory fauna.

5.3 Daisyworld and Rejection of Teleology

Critics (Richard Dawkins, W. Ford Doolittle) objected that a planet cannot evolve homeostatic regulation by natural selection without a population of competing, reproducing planets.

Lovelock and Andrew Watson (1983) answered with Daisyworld, an analytical model: * Two daisy species populate a planet: black (absorbs heat, warms locally) and white (reflects heat, cools locally). * As solar luminosity rises, black daisies dominate the cold early phase, warming the planet; white daisies expand in the late hot phase, cooling the planet. * Global temperature stability emerges entirely from local individual selection without foresight or group selection.

Margulis maintained the scientific boundary: Gaia is not an organism. Gaia is an emergent homeorhetic property of an interconnected planetary ecosystem of ecosystems.

Margulis launched a profound structural challenge to neo-Darwinism:

6.1 The Holobiont and Hologenome

Margulis demonstrated that solitary organisms do not exist in isolation: * The Holobiont: An anatomical host combined with its resident microbial ecosystem. * The Hologenome: The collective genetic sum of host and microbial partners. * Obligate Consortia: * Lichens: Obligate symbiotic composites of fungi (mycobiont) and algae/cyanobacteria (photobiont). * Termites: Retying wood digestion and nitrogen fixation to dense hindgut consortia of protists and bacteria. * Ruminants: Rumen fermentation vats where anaerobic consortia convert cellulose into volatile fatty acids. * Human Holobionts: $\sim 3.8 \times 10^{13}$ bacterial cells outnumbering host cells, encoding $>2$ million unique microbial genes modulating gut immunity, metabolic homeostasis, and neurological signaling.

Audit of empirical and theoretical assertions associated with Lynn Margulis: * V Verified = Verified: Empirically confirmed, validated across methods, modern canon. * C Corroborated = Corroborated: Strong empirical backing, prevailing scientific consensus. * S Single-Source = Speculative: Plausible hypothesis, open debate, incomplete empirical data. * [F] = Falsified: Definitively disproven by subsequent genomic/biochemical data. * [R] = Reframed: Misleading popular caricature rejected; valid under rigorous reframing.

8.1 Cooperative Game Theory and Irreversible Collateral

• Non-Zero-Sum Metabolic Regimes: Classical competition maps to zero-sum games ($A$'s gain is $B$'s loss). Endosymbiosis unlocks non-zero-sum pay-offs: combining anaerobic glycolytic capacity with oxidative phosphorylation yields a $16$-fold increase in ATP per glucose molecule, expanding total system capacity.
• Raising the Cost of Defection to Infinity: In iterated Prisoner's Dilemma games, cooperation collapses under free-riding. In endosymbiosis, Endosymbiotic Gene Transfer (EGT) serves as irreversible collateralization: once the symbiont offloaded essential genes to the host nucleus, neither entity could defect without immediate metabolic death.

8.2 Economics and Corporate M&A (Mergers & Acquisitions)

• Internal R&D vs. Inorganic Acquisition: Organizations facing sudden paradigm shifts face the choice of slow internal trial-and-error R&D (point mutations) or inorganic acquisition of pre-built external capabilities (symbiogenesis). Eukaryogenesis was the corporate acquisition of an established energy utility.
• Post-Merger Overhead Rationalization (EGT): Acquirers eliminate duplicate back-office infrastructure (HR, accounting) by centralizing them at corporate headquarters (the nucleus) while maintaining the acquired engineering engine on-site (the mitochondrion).
• The CoRR Principle in Enterprise Operations: John F. Allen’s CoRR principle mirrors distributed business architecture: centralize long-term strategy and common services, but keep immediate operational decision loops co-located on the production floor where signaling latency causes critical damage.

8.3 Systems Architecture and Software Engineering

• Composition Over Inheritance: Classical object-oriented class inheritance ($A \text{ extends } B$) mirrors bifurcating Darwinian cladograms, leading to brittle, over-coupled hierarchies. Modern software strongly favors composition over inheritance (has-a instead of is-a). The eukaryotic cell is the ultimate triumph of composition: embedding pre-compiled bacterial engines inside an orchestrator.
• Monolith to Microservices: Bacteria operate as single monolithic processes where transcription, translation, and respiration compete in a single shared memory space. Eukaryotes partition tasks into isolated microservices: energy production in isolated containers (mitochondria), information storage behind an authenticated gateway (the nuclear envelope with nuclear pore complexes), and distribution through dedicated message queues (the ER-Golgi network).
• Legacy Protocol Wrapping: Modern systems rarely rewrite stable, low-level legacy binaries; they construct modern API wrappers around them. The eukaryotic nucleus and TOM/TIM protein translocases serve as high-level API wrappers managing an ancient bacterial hardware engine.

8.4 Distributed Systems and Edge Computing

• Biological Edge Computing: Routing all real-time sensor evaluations through a central processor creates bandwidth saturation and latency failures. Organellar DNA retention is biological edge computing: local redox imbalances at the inner membrane are sensed and addressed on-site at millisecond latency, preventing electron leaks and apoptotic failure.
• Homeorhesis vs. Homeostasis: In cybernetics, homeorhesis describes stabilization around an evolving trajectory rather than a static equilibrium set-point. Earth's biosphere maintains habitability not by freezing temperatures, but by dynamically modulating greenhouse flux rates to counterbalance an evolving star.

9.1 Foundational Works by Lynn Margulis

• Sagan, Lynn (1967). "On the Origin of Mitosing Cells." Journal of Theoretical Biology, 14(3), 225–274.
• Margulis, Lynn (1970). Origin of Eukaryotic Cells: Evidence and Research Implications for a Theory of the Origin and Evolution of Microbial, Plant, and Animal Cells on the Precambrian Earth. New Haven: Yale University Press.
• Margulis, Lynn (1981). Symbiosis in Cell Evolution: Life and Its Diverse Microbial Partners. San Francisco: W. H. Freeman & Co. (2nd ed., 1993).
• Margulis, Lynn (1998). Symbiotic Planet: A New Look at Evolution. New York: Basic Books.
• Margulis, Lynn, & Sagan, Dorion (1986). Microcosmos: Four Billion Years of Microbial Evolution. New York: Summit Books.
• Margulis, Lynn, & Sagan, Dorion (2002). Acquiring Genomes: A Theory of the Origins of Species. New York: Basic Books.

9.2 The Gaia Hypothesis (Lovelock & Margulis)

• Lovelock, James E., & Margulis, Lynn (1974). "Atmospheric Homeostasis by and for the Biosphere: The Gaia Hypothesis." Tellus, 26(1–2), 2–10.
• Margulis, Lynn, & Lovelock, James E. (1974). "Biological Modulation of the Earth's Atmosphere." Icarus, 21(4), 471–489.
• Lovelock, James E. (1979). Gaia: A New Look at Life on Earth. Oxford: Oxford University Press.
• Watson, Andrew J., & Lovelock, James E. (1983). "Biological Homeostasis of the Global Environment: The Parable of Daisyworld." Tellus B, 35(4), 284–289.
• Charlson, Robert J., Lovelock, James E., Andreae, Meinrat O., & Warren, Stephen G. (1987). "Oceanic Phytoplankton, Atmospheric Sulphur, Cloud Albedo and Climate." Nature, 326(6114), 655–661.

9.3 Molecular Phylogenomics and Bioenergetics

• Allen, John F. (1992). "Protein Phosphorylation in Regulation of Photosynthesis: An Evolutionary Perspective." Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1098(3), 275–335.
• Allen, John F. (2003). "Why Chloroplasts and Mitochondria Contain Genomes." Comparative and Functional Genomics, 4(1), 31–36.
• Cavalier-Smith, Thomas (1987). "The Simultaneous Origin of Mitochondria and Chloroplasts." Annals of the New York Academy of Sciences, 503(1), 55–71.
• Doolittle, W. Ford (1981). "Is Nature Really Motherly?" The CoEvolution Quarterly, 29, 58–63.
• Gray, Michael W., & Doolittle, W. Ford (1982). "Has the Endosymbiont Hypothesis Been Proven?" Microbiological Reviews, 46(1), 1–42.
• Lake, James A. (1988). "Origin of the Eukaryotic Nucleus Determined by Rate-Invariant Analysis of rRNA Sequences." Nature, 331(6152), 184–186.
• Lane, Nick, & Martin, William (2010). "The Energetics of Genome Complexity." Nature, 467(7318), 929–934.
• Martin, William, & Müller, Miklós (1998). "The Hydrogen Hypothesis for the First Eukaryote." Nature, 392(6671), 37–41.
• Spang, Anja, Saw, Jimmy H., Jørgensen, Steffen L., Zaremba-Niedzwiedzka, Katarzyna, Martijn, Joran, Lind, Anders E., van Eijk, Roel, Schleper, Christa, Guy, Lionel, & Ettema, Thijs J. G. (2015). "Complex Archaea That Bridge the Gap Between Prokaryotes and Eukaryotes." Nature, 521(7551), 173–179.
• Woese, Carl R., & Fox, George E. (1977). "Phylogenetic Structure of the Prokaryotic Domain: The Primary Kingdoms." PNAS, 74(11), 5088–5090.

9.4 Holobionts and the Extended Evolutionary Synthesis

• Bordenstein, Seth R., & Theis, Kevin R. (2015). "Host Biology in Light of the Microbiome: The Hologenome Concept." PLOS Biology, 13(8), e1002226.
• Dawkins, Richard (1982). The Extended Phenotype: The Long Reach of the Gene. Oxford: Oxford University Press.
• Zilber-Rosenberg, Ilana, & Rosenberg, Eugene (2008). "Role of Microorganisms in the Evolution of Animals and Plants: The Hologenome Theory of Evolution." FEMS Microbiology Reviews, 32(5), 723–735.