Symbiogenesis is the merging of two separate organisms to form a single new organism. The idea originated with Konstantin Mereschkowsky in his 1926 book
Symbiogenesis and the Origin of Species, which proposed that
chloroplastChloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve free energy in the form of ATP and reduce NADP to NADPH through a complex set of processes called photosynthesis.The word chloroplast is...
s originate from
cyanobacteriaCyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of bacteria that obtain their energy through photosynthesis. The name "cyanobacteria" comes from the color of the bacteria = blue)...
captured by a
protozoaProtozoa or Cornelius protozoans Protozoa or Cornelius protozoans Protozoa or Cornelius protozoans (from Greek πρῶτον proton "first" and ζῷα zoa "animals"; singular protozoon; (the word "protozoan" is originally an adjective, used as a noun) are microorganisms classified as unicellular eukaryotes....
n. Today both chloroplasts and
mitochondriaIn cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5–10 micrometers in diameter...
are believed to have such an origin; this is the
endosymbiotic theoryThe endosymbiotic theory concerns the origins of mitochondria and plastids , which are organelles of eukaryotic cells. According to this theory, these organelles originated as separate prokaryotic organisms that were taken inside the cell as endosymbionts...
.
In
Acquiring Genomes: A Theory of the Origins of Species,
biologistA biologist is a scientist devoted to and producing results in biology through the study of life.Typically biologists study organisms and their relationship to their environment. Biologists involved in basic research attempt to discover underlying mechanisms that govern how organisms work...
Dr. Lynn MargulisLynn Margulis is an American biologist and University Professor in the Department of Geosciences at the University of Massachusetts Amherst...
argued later that symbiogenesis is a primary force in
evolutionIn biology, evolution is change in the genetic material of a population of organisms from one generation to the next. Though changes produced in any one generation are normally small, differences accumulate with each generation and can, over time, cause substantial changes in the population, a...
.
Symbiogenesis is the merging of two separate organisms to form a single new organism. The idea originated with Konstantin Mereschkowsky in his 1926 book
Symbiogenesis and the Origin of Species, which proposed that
chloroplastChloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve free energy in the form of ATP and reduce NADP to NADPH through a complex set of processes called photosynthesis.The word chloroplast is...
s originate from
cyanobacteriaCyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of bacteria that obtain their energy through photosynthesis. The name "cyanobacteria" comes from the color of the bacteria = blue)...
captured by a
protozoaProtozoa or Cornelius protozoans Protozoa or Cornelius protozoans Protozoa or Cornelius protozoans (from Greek πρῶτον proton "first" and ζῷα zoa "animals"; singular protozoon; (the word "protozoan" is originally an adjective, used as a noun) are microorganisms classified as unicellular eukaryotes....
n. Today both chloroplasts and
mitochondriaIn cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5–10 micrometers in diameter...
are believed to have such an origin; this is the
endosymbiotic theoryThe endosymbiotic theory concerns the origins of mitochondria and plastids , which are organelles of eukaryotic cells. According to this theory, these organelles originated as separate prokaryotic organisms that were taken inside the cell as endosymbionts...
.
Theory of symbiotic relationships driving evolution
In
Acquiring Genomes: A Theory of the Origins of Species,
biologistA biologist is a scientist devoted to and producing results in biology through the study of life.Typically biologists study organisms and their relationship to their environment. Biologists involved in basic research attempt to discover underlying mechanisms that govern how organisms work...
Dr. Lynn MargulisLynn Margulis is an American biologist and University Professor in the Department of Geosciences at the University of Massachusetts Amherst...
argued later that symbiogenesis is a primary force in
evolutionIn biology, evolution is change in the genetic material of a population of organisms from one generation to the next. Though changes produced in any one generation are normally small, differences accumulate with each generation and can, over time, cause substantial changes in the population, a...
. According to her theory, acquisition and accumulation of random
mutationIn biology, a mutation is a randomly derived change to the nucleotide sequence of the genetic material of an organism.Mutations can be caused by copying errors in the genetic material during cell division, or by exposure to mutagens , or can be induced by the organism itself, by cellular processes...
s are not sufficient to explain how inherited variations occur; rather, new
organelleIn cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid membrane....
s, bodies,
organsIn biology and anatomy, an organ is a collection of tissues joined in structural unit to serve a common function ....
, and species arise from symbiogenesis. Whereas the classical interpretation of evolution (the
modern evolutionary synthesisThe modern evolutionary synthesis is a union of ideas from several biological specialties which forms a logical account of evolution. This synthesis has been accepted by nearly all working biologists...
) emphasizes competition as the main force behind evolution, Margulis emphasizes cooperation.
Many ecologists agree, but this idea has little support from other evolutionary biologists . They see little evidence that symbiogenesis has had a major impact on
eukaryoticA eukaryote is an organism whose cells contain complex structures enclosed within membranes. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear envelope, within which the genetic material is carried...
life, or that much of its diversification can be attributed to it. Other than the two examples of mitochondria and chloroplasts, there is no clear evidence of other major traits or transitions that can be attributed to symbiogenesis.
A fundamental principle of modern evolutionary theory is that mutations arise one at a time and either spread through the population or not, depending on whether they offer an individual fitness advantage. Nevertheless, this general case may not apply to all examples of evolutionary change. Indeed, genome mapping techniques have revealed that family trees of the major taxa appear to be extensively cross-linked—possibly due to lateral gene transfer.
Important publications
- Konstantin Mereschkowsky. Symbiogenesis and the Origin of Species. 1926.
- Lynn Margulis. Symbiotic Planet: A New Look at Evolution. Amherst, MA: Perseus Books Group, 1998. ISBN 0-456-07271-2.
- Lynn Margulis, Dorion Sagan. Acquiring Genomes: A Theory of the Origins of Species. Amherst, MA: Perseus Books Group, 2002. ISBN 0-465-04391-7.