Evolution of eukaryotes: Difference between revisions
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For roughly the fist 1.7 billion years of life on Earth consisted of prokaryotes, nucleus-less cells grouped into bacteria and archea. Then 2 billion years, two prokaryotes symbiotically joined to form the more complex ''eukaryotic'' cells that make up all animals, plants, and fungi. | |||
Starting in the 1960s, the biologist Lynn Margulis did much to clarify and make mainstream the theory of the symbiotic origin of eukaryotes.<ref>David Quammen, ''The Tangled Tree: A Radical New History of Life'' (New York: Simon & Schuster, 2018) Part III.</ref> Margulis writes with her co-author (and son) Dorion Sagan, "The creative force of symbiosis produced eukaryotic cells from [[Bacteria|bacteria]]. Hence all larger organisms--protocoists, fungi, animals, and plants--originated symbiogenetically."<ref>Lynn Margulis and Dorion Sagan, ''Acquiring Genomes: A Theory of the Origin of Species'' (New York: Basic Books, 2002), 55-56.</ref> | |||
There are a number of reasons to believe that components of eukaryotic cells originated as independent prokaryotes. The DNA of a eukaryote's component parts, specifically, mitochondria and plastids, is unlike the DNA of the nucleus. Mitochondria and plastids make proteins in ways that prokaryotes do and are affected by drugs that affect prokaryotes. One way that the symbiosis may have occurred is that the host cell may have preyed on and digested the bacteria. A second way is that the host cell and the bacteria may have lived side by side, producing substances for each other, until the host took the other cell inside itself.<ref>Richard Cowen, ''History of Life'', fourth edition (Malden: Blackwell Publishing, 2005), 30-32.</ref> | |||
Science journalist David Quamm explains, "[E]xperts agree nowadays that endosymbiosis played an essential role: somehow a bacterium got captured and domesticated inside another cell, a host, where it became a mitochondrion."<ref>Quammen, ''The Tangled Tree'', Part VII.</ref> | |||
In 2015, however, a group of scientists led by Thijs Ettema proposed that the host cell was a type of archea (not bacteria) they found at the bottom of the Atlantic Ocean between Greenland and Norway. They called the it ''Lokiarchaeum'' and found it to be closely related to eukaryotes.<ref>Quammen, ''The Tangled Tree'', Part VII.</ref> | |||
The evolution of eukaryotes involved epigenetic inheritance according to Eva Jablonka and Marion Lamb: | |||
<blockquote> | |||
Without reliable structural inheritance, the transition would not have been possible: the internal skeleton that was necessary after the prokaryotic cell was lost, the structural elements necessary for mitosis, and the construction of the membranes of the cell and its organelles, all depend on information transmitted through guided assembly.<ref>Eva Jablonka and Marion Lamb, “The Evolution in the major transitions,” ''Journal of Theoretical Biology'' 239 (2006): 236-246. | |||
</blockquote> | |||
<references/> | <references/> | ||
Latest revision as of 16:37, 22 November 2024
For roughly the fist 1.7 billion years of life on Earth consisted of prokaryotes, nucleus-less cells grouped into bacteria and archea. Then 2 billion years, two prokaryotes symbiotically joined to form the more complex eukaryotic cells that make up all animals, plants, and fungi.
Starting in the 1960s, the biologist Lynn Margulis did much to clarify and make mainstream the theory of the symbiotic origin of eukaryotes.[1] Margulis writes with her co-author (and son) Dorion Sagan, "The creative force of symbiosis produced eukaryotic cells from bacteria. Hence all larger organisms--protocoists, fungi, animals, and plants--originated symbiogenetically."[2]
There are a number of reasons to believe that components of eukaryotic cells originated as independent prokaryotes. The DNA of a eukaryote's component parts, specifically, mitochondria and plastids, is unlike the DNA of the nucleus. Mitochondria and plastids make proteins in ways that prokaryotes do and are affected by drugs that affect prokaryotes. One way that the symbiosis may have occurred is that the host cell may have preyed on and digested the bacteria. A second way is that the host cell and the bacteria may have lived side by side, producing substances for each other, until the host took the other cell inside itself.[3]
Science journalist David Quamm explains, "[E]xperts agree nowadays that endosymbiosis played an essential role: somehow a bacterium got captured and domesticated inside another cell, a host, where it became a mitochondrion."[4]
In 2015, however, a group of scientists led by Thijs Ettema proposed that the host cell was a type of archea (not bacteria) they found at the bottom of the Atlantic Ocean between Greenland and Norway. They called the it Lokiarchaeum and found it to be closely related to eukaryotes.[5]
The evolution of eukaryotes involved epigenetic inheritance according to Eva Jablonka and Marion Lamb:
Without reliable structural inheritance, the transition would not have been possible: the internal skeleton that was necessary after the prokaryotic cell was lost, the structural elements necessary for mitosis, and the construction of the membranes of the cell and its organelles, all depend on information transmitted through guided assembly.<ref>Eva Jablonka and Marion Lamb, “The Evolution in the major transitions,” Journal of Theoretical Biology 239 (2006): 236-246.
- ↑ David Quammen, The Tangled Tree: A Radical New History of Life (New York: Simon & Schuster, 2018) Part III.
- ↑ Lynn Margulis and Dorion Sagan, Acquiring Genomes: A Theory of the Origin of Species (New York: Basic Books, 2002), 55-56.
- ↑ Richard Cowen, History of Life, fourth edition (Malden: Blackwell Publishing, 2005), 30-32.
- ↑ Quammen, The Tangled Tree, Part VII.
- ↑ Quammen, The Tangled Tree, Part VII.
