THE TREE OF LIFE
G. C. Williams
California Academy of Sciences
As recently as the mid-1960’s, all the known kinds of living organisms on Earth were aligned with either plants or animals. Many biology textbooks were commonly either botany or zoology texts. Botany covered a potpourri of biodiversity, including bacteria, algae, fungi, and green plants, while zoology covered animals and an enormous assemblage of single-celled organisms called protozoans.
Then,
in 1969 the five kingdom concept was introduced by Robert Whittaker – the five
major kingdoms included three multicellular groups (animals, plants, and fungi),
unicellular organisms (protists), and Monera (bacteria). An important
distinction was made between Prokaryotes
such as bacteria and archaeans (organisms
without membrane-bound organelles in their cells), and all other organisms
known as Eukaryotes (organisms with
membrane-bound organelles such as nuclei and mitochondria).
Also
at the end of the 1960s decade, Lynn Margulis proposed the the Endosymbiotic Theory – an
evolutionary theory that explains the origin of eukaryotic cells from
prokaryotes, in that several organelles of eukaryotes (such as the nucleus and
mitochondria) originated as a symbiosis between separate prokaryotes.
In recent years,
ever-more-sophisticated molecular techniques and the ability to completely
sequence genomes have revolutionized our thinking regarding the biodiversity of
life. We now recognize an overwhelming complexity of life. Instead of the
simple dichotomy of plants and animals, we have over 100 groups of eukaryotic
organisms that make up only one part of the tree of life. Eukaryotes join two
groups of prokaryotes (Bacteria and Archaea) in an overall view of life on our planet.
THE TREE OF LIFE
G. C. Williams
California Academy of Sciences
As recently as the mid-1960’s, all the known kinds of living organisms on Earth were aligned with either plants or animals. Many biology textbooks were commonly either botany or zoology texts. Botany covered a potpourri of biodiversity, including bacteria, algae, fungi, and green plants, while zoology covered animals and an enormous assemblage of single-celled organisms called protozoans.
Then,
in 1969 the five kingdom concept was introduced by Robert Whittaker – the five
major kingdoms included three multicellular groups (animals, plants, and fungi),
unicellular organisms (protists), and Monera (bacteria). An important
distinction was made between Prokaryotes
such as bacteria and archaeans (organisms
without membrane-bound organelles in their cells), and all other organisms
known as Eukaryotes (organisms with
membrane-bound organelles such as nuclei and mitochondria).
Also
at the end of the 1960s decade, Lynn Margulis proposed the the Endosymbiotic Theory – an
evolutionary theory that explains the origin of eukaryotic cells from
prokaryotes, in that several organelles of eukaryotes (such as the nucleus and
mitochondria) originated as a symbiosis between separate prokaryotes.
In recent years,
ever-more-sophisticated molecular techniques and the ability to completely
sequence genomes have revolutionized our thinking regarding the biodiversity of
life. We now recognize an overwhelming complexity of life. Instead of the
simple dichotomy of plants and animals, we have over 100 groups of eukaryotic
organisms that make up only one part of the tree of life. Eukaryotes join two
groups of prokaryotes (Bacteria and Archaea) in an overall view of life on our planet.
For further information see: The Tree of Life Gets a Makeover (https://www.sciencenews.org/article/tree-life-gets-makeover)
Plants and animals represent only two slices of the
Eukaryote pie of the over 100 slices now recognized
A simplified Hillis plot of the tree of life, based on completely sequenced genomes – Bacteria (blue); Archaea (green); Eukaryotes (red)
A simplified tree of life for Eukaryotes
For further information see: The Tree of Life Gets a Makeover (https://www.sciencenews.org/article/tree-life-gets-makeover)
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| Plants and animals represent only two slices of the Eukaryote pie of the over 100 slices now recognized |
 |
| A simplified Hillis plot of the tree of life, based on completely sequenced genomes – Bacteria (blue); Archaea (green); Eukaryotes (red) |
 A simplified tree of life for Eukaryotes |
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