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Common descent is a concept in
evolutionary biology Evolutionary biology is the subfield of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interacti ...
applicable when one species is the ancestor of two or more species later in time. All living beings are in fact descendants of a unique ancestor commonly referred to as the
last universal common ancestor The last universal common ancestor or last universal cellular ancestor (LUCA), also called the last universal ancestor (LUA), is the most recent population of organisms from which all organisms now living on Earth have a common descent Common ...
(LUCA) of all
life Life is a characteristic that distinguishes physical entities that have biological processes, such as Cell signaling, signaling and self-sustaining processes, from those that do not, either because such functions have ceased (they have Death ...

life
on
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wit ...

Earth
, according to modern evolutionary biology. Common descent is an effect of
speciation Speciation is the evolution Evolution is change in the Heredity, heritable Phenotypic trait, characteristics of biological populations over successive generations. These characteristics are the Gene expression, expressions of genes that are ...

speciation
, in which multiple species derive from a single ancestral population. The more recent the ancestral population two species have in common, the more closely are they related. The most recent common ancestor of all currently living organisms is the last universal ancestor, which lived about 3.9 billion years ago. The two earliest pieces of evidence for life on Earth are
graphite Graphite (), archaically referred to as plumbago, is a crystalline form of the element carbon Carbon (from la, carbo "coal") is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table ...

graphite
found to be
biogenic A biogenic substance is a product made by or of life forms. While the term originally was specific to metabolite compounds that had toxic effects on other organisms, it has developed to encompass any constituents, secretions, and metabolites of pla ...
in 3.7 billion-year-old
metasedimentary rock In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it is composed, and the processes ...
s discovered in western
Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an * * * within the and the , located between the and oceans, east of the . Though a part of the continent of , Greenland has been politically and culturally associated with (spec ...

Greenland
and
microbial mat The cyanobacterial algal mat, salty lake on the White Sea">algal_mat.html" ;"title="cyanobacterial algal mat">cyanobacterial algal mat, salty lake on the White Sea seaside A microbial mat is a multi-layered sheet of microorganisms, mainly bacteria ...
fossil A fossil (from Classical Latin Classical Latin is the form of Latin, Latin language recognized as a Literary language, literary standard language, standard by writers of the late Roman Republic and early Roman Empire. It was used from 75 ...

fossil
s found in 3.48 billion-year-old
sandstone Sandstone is a clastic sedimentary rock of a clast (sand grain), derived from a basalt Basalt (, ) is a fine-grained extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron ('' mafic ' ...

sandstone
discovered in
Western Australia Western Australia (abbreviated as WA) is a States and territories of Australia, state occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, and the S ...

Western Australia
. All currently living organisms on Earth share a common heritage, though the suggestion of substantial
horizontal gene transfer Horizontal gene transfer (HGT) or lateral gene transfer (LGT) is the movement of genetic material between unicellular A unicellular organism, also known as a single-celled organism, is an organism In biology, an organism (from Ancient G ...
during early evolution has led to questions about the
monophyly 300px, A cladogram of the primates, showing a ''monophyletic'' taxon: ''the simians'' (in yellow); a ''paraphyletic'' taxon: ''the prosimians'' (in cyan, including the red patch); and a ''polyphyletic'' group: ''the night-active primates, i.e., ...
(single ancestry) of life. 6,331 groups of
gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to describe the Mendelian_inheritance#History, Mendelian units of heredity..." (Greek language, Greek) meaning ''generation'' or ''birth'' ) is a basic unit of her ...

gene
s common to all living animals have been identified; these may have arisen from a single
common ancestor Common descent is a concept in evolutionary biology Evolutionary biology is the subfield of biology that studies the evolution, evolutionary processes (natural selection, common descent, speciation) that produced the Biodiversity, diversity ...

common ancestor
that lived 650 million years ago in the
Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of History of the Earth, Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the ...

Precambrian
. Universal common descent through an
evolution Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; either through asexual reproduction or sexual reproduction, ...

evolution
ary process was first proposed by the British
naturalist Natural history is a domain of inquiry involving organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classif ...

naturalist
Charles Darwin Charles Robert Darwin (; ; 12 February 1809 – 19 April 1882) was an English , and , best known for his contributions to the science of . His proposition that all species of life have descended from is now widely accepted and cons ...

Charles Darwin
in the concluding sentence of his 1859 book ''
On the Origin of Species ''On the Origin of Species'' (or, more completely, ''On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life''),The book's full original title was ''On the Origin of Species by Me ...
'':


History

The idea that all living things (including things considered non-living by science) are related is a recurring theme in many indigenous worldviews across the world. Later on, in the 1740s, the French
mathematician A mathematician is someone who uses an extensive knowledge of mathematics Mathematics (from Greek: ) includes the study of such topics as numbers ( and ), formulas and related structures (), shapes and spaces in which they are contained ( ...

mathematician
Pierre Louis Maupertuis Pierre Louis Moreau de Maupertuis (; ; 1698 – 27 July 1759) was a French mathematician, philosopher and man of letters An intellectual is a person who engages in critical thinking, research, and Human self-reflection, reflection about t ...
arrived at the idea that all organisms had a common ancestor, and had diverged through random variation and
natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype right , Here the relation between genotype and phenotype is illustrated, using a Punnett square, for the character of peta ...
. In ''Essai de cosmologie'' (1750), Maupertuis noted:
May we not say that, in the fortuitous combination of the productions of Nature, since only those creatures ''could'' survive in whose organizations a certain degree of adaptation was present, there is nothing extraordinary in the fact that such adaptation is actually found in all these species which now exist? Chance, one might say, turned out a vast number of individuals; a small proportion of these were organized in such a manner that the animals' organs could satisfy their needs. A much greater number showed neither adaptation nor order; these last have all perished.... Thus the species which we see today are but a small part of all those that a blind destiny has produced.
In 1790, the philosopher
Immanuel Kant Immanuel Kant (, , ; 22 April 1724 – 12 February 1804) was a German Philosophy, philosopher and one of the central Age of Enlightenment, Enlightenment thinkers. Kant's comprehensive and systematic works in epistemology, metaphysics, ethi ...

Immanuel Kant
wrote in ''Kritik der Urteilskraft'' (''
Critique of Judgment The ''Critique of Judgment'' (), also translated as the ''Critique of the Power of Judgment'', is a 1790 book by the German philosopher Immanuel Kant Immanuel Kant (, ; ; 22 April 1724 – 12 February 1804) was a German Philosophy, philo ...
'') that the similarity of animal forms implies a common original type, and thus a common parent. In 1794, Charles Darwin's grandfather,
Erasmus Darwin Erasmus Robert Darwin (12 December 173118 April 1802) was an English physician. One of the key thinkers of the Midlands Enlightenment, he was also a natural philosophy, natural philosopher, physiology, physiologist, Society for Effecting the A ...
asked:
uld it be too bold to imagine, that in the great length of time, since the earth began to exist, perhaps millions of ages before the commencement of the history of mankind, would it be too bold to imagine, that all warm-blooded animals have arisen from one living filament, which endued with animality, with the power of acquiring new parts attended with new propensities, directed by irritations, sensations, volitions, and associations; and thus possessing the faculty of continuing to improve by its own inherent activity, and of delivering down those improvements by generation to its posterity, world without end?
Charles Darwin Charles Robert Darwin (; ; 12 February 1809 – 19 April 1882) was an English , and , best known for his contributions to the science of . His proposition that all species of life have descended from is now widely accepted and cons ...

Charles Darwin
's views about common descent, as expressed in ''
On the Origin of Species ''On the Origin of Species'' (or, more completely, ''On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life''),The book's full original title was ''On the Origin of Species by Me ...
'', were that it was probable that there was only one progenitor for all life forms:
Therefore I should infer from analogy that probably all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed.
But he precedes that remark by, "Analogy would lead me one step further, namely, to the belief that all animals and plants have descended from some one prototype. But analogy may be a deceitful guide." And in the subsequent edition, he asserts rather,
"We do not know all the possible transitional gradations between the simplest and the most perfect organs; it cannot be pretended that we know all the varied means of Distribution during the long lapse of years, or that we know how imperfect the Geological Record is. Grave as these several difficulties are, in my judgment they do not overthrow the theory of descent from a few created forms with subsequent modification".
Common descent was widely accepted amongst the
scientific community The scientific community is a diverse network of interacting scientist A scientist is a person who conducts Scientific method, scientific research to advance knowledge in an Branches of science, area of interest. In classical antiquity, there w ...
after Darwin's publication. In 1907,
Vernon Kellogg Vernon Lyman Kellogg (December 1, 1867 in Emporia, Kansas – August 8, 1937 in Hartford, Connecticut) was an American entomologist, evolutionary biologist, and science administrator. His father was Lyman Beecher Kellogg, first president of the Kan ...
commented that "practically no naturalists of position and recognized attainment doubt the theory of descent." In 2008, biologist T. Ryan Gregory noted that:
No reliable observation has ever been found to contradict the general notion of common descent. It should come as no surprise, then, that the scientific community at large has accepted evolutionary descent as a historical reality since Darwin’s time and considers it among the most reliably established and fundamentally important facts in all of science.


Evidence


Common biochemistry

All known forms of life are based on the same fundamental biochemical organization: genetic information encoded in
DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral gro ...

DNA
, transcribed into
RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Repe ...

RNA
, through the effect of
protein Proteins are large s and s that comprise one or more long chains of . Proteins perform a vast array of functions within organisms, including , , , providing and , and from one location to another. Proteins differ from one another primarily ...

protein
- and RNA-
enzyme Enzymes () are s that act as s (biocatalysts). Catalysts accelerate . The molecules upon which enzymes may act are called , and the enzyme converts the substrates into different molecules known as . Almost all in the need in order to occu ...

enzyme
s, then translated into proteins by (highly similar)
ribosome Ribosomes ( ), also called Palade granules, are , found within all , that perform (mRNA translation). Ribosomes link together in the order specified by the s of (mRNA) molecules to form chains. Ribosomes consist of two major components: the ...

ribosome
s, with
ATP ATP may refer to: Companies and organizations * Association of Tennis Professionals * American Technical Publishers * ', a Danish pension * Armenia Tree Project * Association for Transpersonal Psychology * ATP architects engineers office * ATP ...

ATP
, NADPH and others as energy sources. Analysis of small sequence differences in widely shared substances such as
cytochrome c The cytochrome complex, or cyt ''c'', is a small hemeprotein found loosely associated with the inner membrane of the mitochondrion A mitochondrion (, plural mitochondria) is a double membrane-bound organelle In cell biology, an organelle i ...

cytochrome c
further supports universal common descent. Some 23 proteins are found in all organisms, serving as
enzyme Enzymes () are s that act as s (biocatalysts). Catalysts accelerate . The molecules upon which enzymes may act are called , and the enzyme converts the substrates into different molecules known as . Almost all in the need in order to occu ...

enzyme
s carrying out core functions like DNA replication. The fact that only one such set of enzymes exists is convincing evidence of a single ancestry. 6,331
gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to describe the Mendelian_inheritance#History, Mendelian units of heredity..." (Greek language, Greek) meaning ''generation'' or ''birth'' ) is a basic unit of her ...

gene
s common to all living animals have been identified; these may have arisen from a single
common ancestor Common descent is a concept in evolutionary biology Evolutionary biology is the subfield of biology that studies the evolution, evolutionary processes (natural selection, common descent, speciation) that produced the Biodiversity, diversity ...

common ancestor
that lived 650 million years ago in the
Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of History of the Earth, Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the ...

Precambrian
.


Common genetic code

The
genetic code The genetic code is the set of rules used by living to information encoded within genetic material ( or sequences of nucleotide triplets, or codons) into s. Translation is accomplished by the , which links s in an order specified by (mRNA), u ...

genetic code
(the "translation table" according to which DNA information is translated into
amino acid Amino acids are organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, c ...

amino acid
s, and hence proteins) is nearly identical for all known lifeforms, from
bacteria Bacteria (; common noun bacteria, singular bacterium) are a type of biological cell The cell (from Latin ''cella'', meaning "small room") is the basic structural, functional, and biological unit of all known organisms. Cells are the sm ...

bacteria
and
archaea Archaea ( ; singular archaeon ) constitute a domain Domain may refer to: Mathematics *Domain of a function, the set of input values for which the (total) function is defined **Domain of definition of a partial function **Natural domain of a pa ...

archaea
to
animal Animals (also called Metazoa) are organisms that form the Animalia. With few exceptions, animals , , are , can , and grow from a hollow sphere of , the , during . Over 1.5 million animal have been —of which around 1 million are —b ...

animal
s and
plant Plants are predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energy that, through cellular respiration, can later be released to fuel ...

plant
s. The universality of this code is generally regarded by biologists as definitive evidence in favor of universal common descent. The way that
codon The genetic code is the set of rules used by living cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or reli ...

codon
s (DNA triplets) are mapped to
amino acid Amino acids are organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, c ...

amino acid
s seems to be strongly optimised. Richard Egel argues that in particular the
hydrophobic In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds composed of at ...
(non-polar) side-chains are well organised, suggesting that these enabled the earliest organisms to create
peptide Peptides (from Greek language Greek (modern , romanized: ''Elliniká'', Ancient Greek, ancient , ''Hellēnikḗ'') is an independent branch of the Indo-European languages, Indo-European family of languages, native to Greece, Cyprus, Albania, ...
s with water-repelling regions able to support the essential electron exchange (
redox (mild reducing agent) are added to powdered potassium permanganate Potassium permanganate is an inorganic compound with the chemical formula KMnO4 and composed of potassium ion, K+ and permanganate, . It is a purplish-black crystalline salt, ...

redox
) reactions for energy transfer.


Selectively neutral similarities

Similarities which have no adaptive relevance cannot be explained by
convergent evolution Convergent evolution is the independent evolution Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; eithe ...
, and therefore they provide compelling support for universal common descent. Such evidence has come from two areas:
amino acid Amino acids are organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, c ...

amino acid
sequences and DNA sequences. Proteins with the same three-dimensional structure need not have identical amino acid sequences; any irrelevant similarity between the sequences is evidence for common descent. In certain cases, there are several
codon The genetic code is the set of rules used by living cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or reli ...

codon
s (DNA triplets) that code redundantly for the same amino acid. Since many species use the same codon at the same place to specify an amino acid that can be represented by more than one codon, that is evidence for their sharing a recent common ancestor. Had the amino acid sequences come from different ancestors, they would have been coded for by any of the redundant codons, and since the correct amino acids would already have been in place,
natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype right , Here the relation between genotype and phenotype is illustrated, using a Punnett square, for the character of peta ...
would not have driven any change in the codons, however much time was available.
Genetic drift Genetic drift (allelic drift or the Sewall Wright effect) is the change in the frequency of an existing gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to describe the Mendelian_inheritance#History, M ...

Genetic drift
could change the codons, but it would be extremely unlikely to make all the redundant codons in a whole sequence match exactly across multiple lineages. Similarly, shared nucleotide sequences, especially where these are apparently neutral such as the positioning of
intron An intron (for ''intragenic region'') is any nucleotide sequence A nucleic acid sequence is a succession of bases signified by a series of a set of five different letters that indicate the order of nucleotides Nucleotides are organic molecul ...

intron
s and
pseudogene Pseudogenes are nonfunctional segments of DNA The structure of part of a DNA double helix Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, wh ...
s, provide strong evidence of common ancestry.


Other similarities

Biologists often point to the universality of many aspects of cellular life as supportive evidence to the more compelling evidence listed above. These similarities include the energy carrier
adenosine triphosphate Adenosine triphosphate (ATP) is an and that provides energy to drive many processes in living , such as muscle contraction, nerve impulse propagation, condensate dissolution, and chemical synthesis. Found in all known forms of life, ATP is ofte ...

adenosine triphosphate
(ATP), and the fact that all amino acids found in proteins are
left-handed In human biology Human biology is an interdisciplinary area of academic study that examines humans through the influences and interplay of many diverse fields such as human genetics, genetics, human evolution, evolution, human physiology, physi ...
. It is, however, possible that these similarities resulted because of the laws of physics and chemistry - rather than through universal common descent - and therefore resulted in convergent evolution. In contrast, there is evidence for homology of the central subunits of Transmembrane ATPases throughout all living organisms, especially how the rotating elements are bound to the membrane. This supports the assumption of a LUCA as a cellular organism, although primordial membranes may have been semipermeable and evolved later to the membranes of modern bacteria, and on a second path to those of modern archaea also.


Phylogenetic trees

Another important piece of evidence is from detailed phylogenetic trees (i.e., "genealogic trees" of species) mapping out the proposed divisions and common ancestors of all living species. In 2010, Douglas L. Theobald published a statistical analysis of available genetic data, mapping them to phylogenetic trees, that gave "strong quantitative support, by a formal test, for the unity of life." Traditionally, these trees have been built using morphological methods, such as appearance,
embryology Embryology (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 mi ...
, etc. Recently, it has been possible to construct these trees using molecular data, based on similarities and differences between genetic and protein sequences. All these methods produce essentially similar results, even though most
genetic variation thumb File:Genetic Variation and Inheritance.svg, Parents have similar gene coding in this specific situation where they reproduce and variation in the offspring is seen. Offspring containing the variation also reproduce and passes down traits t ...

genetic variation
has no influence over external morphology. That phylogenetic trees based on different types of information agree with each other is strong evidence of a real underlying common descent.


Potential objections


Gene exchange clouds phylogenetic analysis

Theobald noted that substantial
horizontal gene transfer Horizontal gene transfer (HGT) or lateral gene transfer (LGT) is the movement of genetic material between unicellular A unicellular organism, also known as a single-celled organism, is an organism In biology, an organism (from Ancient G ...
could have occurred during early evolution. Bacteria today remain capable of gene exchange between distantly-related lineages. This weakens the basic assumption of phylogenetic analysis, that similarity of genomes implies common ancestry, because sufficient gene exchange would allow lineages to share much of their genome whether or not they shared an ancestor (monophyly). This has led to questions about the single ancestry of life. However, biologists consider it very unlikely that completely unrelated proto-organisms could have exchanged genes, as their different coding mechanisms would have resulted only in garble rather than functioning systems. Later, however, many organisms all derived from a single ancestor could readily have shared genes that all worked in the same way, and it appears that they have.


Convergent evolution

If early organisms had been driven by the same environmental conditions to evolve similar biochemistry convergently, they might independently have acquired similar genetic sequences. Theobald's "formal test" was accordingly criticised by Takahiro Yonezawa and colleagues for not including consideration of convergence. They argued that Theobald's test was insufficient to distinguish between the competing hypotheses. Theobald has defended his method against this claim, arguing that his tests distinguish between phylogenetic structure and mere sequence similarity. Therefore, Theobald argued, his results show that "real universally conserved proteins are homologous."


See also

* ''
The Ancestor's Tale ''The Ancestor's Tale: A Pilgrimage to the Dawn of Life'' is a science book by Richard Dawkins Richard Dawkins (born 26 March 1941) is a British ethologist, evolutionary biologist, atheist thinker, and author An author is the crea ...
'' * Urmetazoan


Bibliography

* * The book is available fro
The Complete Work of Charles Darwin Online
Retrieved 2015-11-23. * Retrieved 2015-11-23. * * * *


Notes


References


External links


29+ Evidences for Macroevolution: The Scientific Case for Common Descent
from the
TalkOrigins Archive The TalkOrigins Archive is a website A website (also written as web site) is a collection of web page A web page (or webpage) is a hypertext File:Douglas Engelbart in 2008.jpg, Douglas Engelbart in 2009, at the 40th anniversary cele ...
.
The Tree of Life Web Project
{{DEFAULTSORT:Common Descent Evolutionary biology Descent Last common ancestors