Symbiogenesis
Encyclopedia
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 chloroplast
s originate from cyanobacteria captured by a protozoa
n. Ivan Wallin also supported this concept in his book “Symbionticism and the Origins of Species." He suggested that bacteria might be the cause of the origin of species, and that species creation may occur through endosymbiosis. Today both chloroplasts and mitochondria
are believed to have such an origin; this is the endosymbiotic theory
.
In Acquiring Genomes: A Theory of the Origins of Species, biologist
Lynn Margulis
argued later that symbiogenesis is a primary force in evolution
. According to her theory, acquisition and accumulation of random mutation
s are not sufficient to explain how inherited variations occur; rather, new organelle
s, bodies, organs
, and species arise from symbiogenesis. Whereas the classical interpretation of evolution (the modern evolutionary synthesis
) emphasizes competition as the main force behind evolution, Margulis emphasizes cooperation. She argues that bacteria along with other microorganisms helped create the conditions that we require for life, such as oxygen. Margulis believes that these microorganisms make up a major component in Earth’s biomass and that they are the reason current conditions on earth are maintained. She also believes that the DNA in the cytoplasm of animal, plant, fungal and protist cells, rather than resulting from mutations, resulted from genes from bacteria that became organelles. She claimed that bacteria are able to exchange genes more quickly and more easily, and because of this, they are more versatile, which is why life was able to evolve so quickly.
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.
Chloroplast
Chloroplasts 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.Chloroplasts are green...
s originate from cyanobacteria captured by a protozoa
Protozoa
Protozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...
n. Ivan Wallin also supported this concept in his book “Symbionticism and the Origins of Species." He suggested that bacteria might be the cause of the origin of species, and that species creation may occur through endosymbiosis. Today both chloroplasts and mitochondria
Mitochondrion
In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5 to 1.0 micrometers in diameter...
are believed to have such an origin; this is the endosymbiotic theory
Endosymbiotic theory
The endosymbiotic theory concerns the mitochondria, plastids , and possibly other organelles of eukaryotic cells. According to this theory, certain organelles originated as free-living bacteria that were taken inside another cell as endosymbionts...
.
In Acquiring Genomes: A Theory of the Origins of Species, biologist
Biologist
A 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...
Lynn Margulis
Lynn Margulis
Lynn Margulis was an American biologist and University Professor in the Department of Geosciences at the University of Massachusetts Amherst. She is best known for her theory on the origin of eukaryotic organelles, and her contributions to the endosymbiotic theory, which is now generally accepted...
argued later that symbiogenesis is a primary force in evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
. According to her theory, acquisition and accumulation of random mutation
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
s are not sufficient to explain how inherited variations occur; rather, new organelle
Organelle
In 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 bilayer....
s, bodies, organs
Organ (anatomy)
In biology, an organ is a collection of tissues joined in structural unit to serve a common function. Usually there is a main tissue and sporadic tissues . The main tissue is the one that is unique for the specific organ. For example, main tissue in the heart is the myocardium, while sporadic are...
, and species arise from symbiogenesis. Whereas the classical interpretation of evolution (the modern evolutionary synthesis
Modern evolutionary synthesis
The modern evolutionary synthesis is a union of ideas from several biological specialties which provides a widely accepted account of evolution...
) emphasizes competition as the main force behind evolution, Margulis emphasizes cooperation. She argues that bacteria along with other microorganisms helped create the conditions that we require for life, such as oxygen. Margulis believes that these microorganisms make up a major component in Earth’s biomass and that they are the reason current conditions on earth are maintained. She also believes that the DNA in the cytoplasm of animal, plant, fungal and protist cells, rather than resulting from mutations, resulted from genes from bacteria that became organelles. She claimed that bacteria are able to exchange genes more quickly and more easily, and because of this, they are more versatile, which is why life was able to evolve so quickly.
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.