Editing Heterotroph (section)

== Origin and diversification ==
The chemical [[Origin of Life|origin of life]] hypothesis suggests that life originated in a [[Primordial soup|prebiotic soup]] with heterotrophs.<ref name=":03">{{Cite journal |last=Bada |first=Jeffrey L. |date=2013 |title=New insights into prebiotic chemistry from Stanley Miller's spark discharge experiments |url=http://xlink.rsc.org/?DOI=c3cs35433d |journal=Chemical Society Reviews |language=en |volume=42 |issue=5 |pages=2186–2196 |doi=10.1039/c3cs35433d |pmid=23340907 |bibcode=2013CSRev..42.2186B |issn=0306-0012}}</ref> The summary of this theory is as follows: early Earth had a highly [[reducing atmosphere]] and energy sources such as electrical energy in the form of lightning, which resulted in reactions that formed simple [[organic compound]]s, which further reacted to form more complex compounds and eventually resulted in life.<ref>{{Cite journal |last=Bracher |first=Paul J. |date=2015 |title=Primordial soup that cooks itself |url=http://www.nature.com/articles/nchem.2219 |journal=Nature Chemistry |language=en |volume=7 |issue=4 |pages=273–274 |doi=10.1038/nchem.2219 |pmid=25803461 |bibcode=2015NatCh...7..273B |issn=1755-4330}}</ref><ref>{{Citation |last=Lazcano |first=Antonio |title=Primordial Soup |date=2015 |url=http://link.springer.com/10.1007/978-3-662-44185-5_1275 |encyclopedia=Encyclopedia of Astrobiology |pages=2010–2014 |editor-last=Gargaud |editor-first=Muriel |place=Berlin, Heidelberg |publisher=Springer Berlin Heidelberg |language=en |doi=10.1007/978-3-662-44185-5_1275 |bibcode=2015enas.book.2010L |isbn=978-3-662-44184-8 |access-date=2022-04-23 |editor2-last=Irvine |editor2-first=William M. |editor3-last=Amils |editor3-first=Ricardo |editor4-last=Cleaves |editor4-first=Henderson James}}</ref> Alternative theories of an autotrophic origin of life contradict this theory.<ref>{{Cite journal |last1=Schönheit |first1=Peter |last2=Buckel |first2=Wolfgang |last3=Martin |first3=William F. |date=2016 |title=On the Origin of Heterotrophy |url=https://linkinghub.elsevier.com/retrieve/pii/S0966842X15002292 |journal=Trends in Microbiology |language=en |volume=24 |issue=1 |pages=12–25 |doi=10.1016/j.tim.2015.10.003|pmid=26578093 }}</ref>

The theory of a chemical origin of life beginning with heterotrophic life was first proposed in 1924 by [[Alexander Oparin|Alexander Ivanovich Oparin]], and eventually published "The Origin of Life."<ref>{{Cite journal |last1=Sanger |first1=F. |last2=Thompson |first2=E. O. P. |date=1953-02-01 |title=The amino-acid sequence in the glycyl chain of insulin. 1. The identification of lower peptides from partial hydrolysates |url=http://dx.doi.org/10.1042/bj0530353 |journal=Biochemical Journal |volume=53 |issue=3 |pages=353–366 |doi=10.1042/bj0530353 |pmid=13032078 |pmc=1198157 |issn=0306-3283}}</ref> It was independently proposed for the first time in English in 1929 by [[J. B. S. Haldane|John Burdon Sanderson Haldane]].<ref>Haldane, J.B.S. (1929) The Origin of Life. The Rationalist Annual, 3, 3–10.</ref> While these authors agreed on the gasses present and the progression of events to a point, Oparin championed a progressive complexity of organic matter prior to the formation of cells, while Haldane had more considerations about the concept of genes as units of heredity and the possibility of light playing a role in chemical synthesis ([[autotroph]]y).<ref>{{Cite journal |last=Tirard |first=Stéphane |date=2017 |title=J. B. S. Haldane and the origin of life |url=http://link.springer.com/10.1007/s12041-017-0831-6 |journal=Journal of Genetics |language=en |volume=96 |issue=5 |pages=735–739 |doi=10.1007/s12041-017-0831-6 |pmid=29237880 |s2cid=28775520 |issn=0022-1333}}</ref>  

Evidence grew to support this theory in 1953, when [[Stanley Miller]] conducted an [[Miller–Urey experiment|experiment]] in which he added gasses that were thought to be present on [[early Earth]] – water (H<sub>2</sub>O), methane (CH<sub>4</sub>), ammonia (NH<sub>3</sub>), and hydrogen (H<sub>2</sub>) – to a flask and stimulated them with electricity that resembled lightning present on early Earth.<ref>{{Cite journal |last=Miller |first=Stanley L. |date=1953-05-15 |title=A Production of Amino Acids Under Possible Primitive Earth Conditions |url=https://www.science.org/doi/10.1126/science.117.3046.528 |journal=Science |language=en |volume=117 |issue=3046 |pages=528–529 |doi=10.1126/science.117.3046.528 |pmid=13056598 |bibcode=1953Sci...117..528M |issn=0036-8075}}</ref> The experiment resulted in the discovery that early Earth conditions were supportive of the production of amino acids, with recent re-analyses of the data recognizing that over 40 different amino acids were produced, including several not currently used by life.<ref name=":03" /> This experiment heralded the beginning of the field of synthetic prebiotic chemistry, and is now known as the [[Miller–Urey experiment]].<ref>{{Cite journal |last1=Lazcano |first1=Antonio |last2=Bada |first2=Jeffrey L. |title=The 1953 Stanley L. Miller experiment: Fifty years of prebiotic organic chemistry |date=2003 |url=http://link.springer.com/10.1023/A:1024807125069 |journal=Origins of Life and Evolution of the Biosphere |volume=33 |issue=3 |pages=235–242 |doi=10.1023/A:1024807125069|pmid=14515862 |bibcode=2003OLEB...33..235L |s2cid=19515024 }}</ref>

On early Earth, oceans and shallow waters were rich with organic molecules that could have been used by primitive heterotrophs.<ref name=":12">{{Cite journal |last1=Preiner |first1=Martina |last2=Asche |first2=Silke |last3=Becker |first3=Sidney |last4=Betts |first4=Holly C. |last5=Boniface |first5=Adrien |last6=Camprubi |first6=Eloi |last7=Chandru |first7=Kuhan |last8=Erastova |first8=Valentina |last9=Garg |first9=Sriram G. |last10=Khawaja |first10=Nozair |last11=Kostyrka |first11=Gladys |date=2020-02-26 |title=The Future of Origin of Life Research: Bridging Decades-Old Divisions |journal=Life |volume=10 |issue=3 |pages=20 |doi=10.3390/life10030020 |pmid=32110893 |pmc=7151616 |issn=2075-1729|doi-access=free |bibcode=2020Life...10...20P }}</ref> This method of obtaining energy was energetically favorable until organic carbon became more scarce than inorganic carbon, providing a potential evolutionary pressure to become autotrophic.<ref name=":12" /><ref>{{Citation |last=Jordan |first=Carl F |title=A Thermodynamic View of Evolution |url=http://dx.doi.org/10.1007/978-3-030-85186-6_12 |work=Evolution from a Thermodynamic Perspective |year=2022 |pages=157–199 |place=Cham |publisher=Springer International Publishing |doi=10.1007/978-3-030-85186-6_12 |isbn=978-3-030-85185-9 |access-date=2022-04-23}}</ref> Following the evolution of autotrophs, heterotrophs were able to utilize them as a food source instead of relying on the limited nutrients found in their environment.<ref name=":22">{{Cite journal |last1=Zachar |first1=István |last2=Boza |first2=Gergely |date=2020-02-01 |title=Endosymbiosis before eukaryotes: mitochondrial establishment in protoeukaryotes |url=http://dx.doi.org/10.1007/s00018-020-03462-6 |journal=Cellular and Molecular Life Sciences |volume=77 |issue=18 |pages=3503–3523 |doi=10.1007/s00018-020-03462-6 |pmid=32008087 |pmc=7452879 |issn=1420-682X}}</ref> Eventually, autotrophic and heterotrophic cells were engulfed by these early heterotrophs and formed a [[Symbiosis|symbiotic]] relationship.<ref name=":22" /> The [[Endosymbiont|endosymbiosis]] of autotrophic cells is suggested to have evolved into the [[chloroplast]]s while the endosymbiosis of smaller heterotrophs developed into the [[Mitochondrion|mitochondria]], allowing the differentiation of tissues and development into multicellularity. This advancement allowed the further diversification of heterotrophs.<ref name=":22" /> Today, many heterotrophs and autotrophs also utilize [[Mutualism (biology)|mutualistic]] relationships that provide needed resources to both organisms.<ref>{{Cite journal |last1=Okie |first1=Jordan G. |last2=Smith |first2=Val H. |last3=Martin-Cereceda |first3=Mercedes |date=2016-05-25 |title=Major evolutionary transitions of life, metabolic scaling and the number and size of mitochondria and chloroplasts |url=http://dx.doi.org/10.1098/rspb.2016.0611 |journal=Proceedings of the Royal Society B: Biological Sciences |volume=283 |issue=1831 |pages=20160611 |doi=10.1098/rspb.2016.0611 |pmid=27194700 |pmc=4892803 |issn=0962-8452}}</ref> One example of this is the mutualism between corals and algae, where the former provides protection and necessary compounds for photosynthesis while the latter provides oxygen.<ref>{{Cite journal |last1=Knowlton |first1=Nancy |last2=Rohwer |first2=Forest |date=2003 |title=Multispecies Microbial Mutualisms on Coral Reefs: The Host as a Habitat |url=http://dx.doi.org/10.1086/378684 |journal=The American Naturalist |volume=162 |issue=S4 |pages=S51–S62 |doi=10.1086/378684 |pmid=14583857 |bibcode=2003ANat..162S..51K |s2cid=24127308 |issn=0003-0147}}</ref>

However this hypothesis is controversial as CO<sub>2</sub> was the main carbon source at the early Earth, suggesting that early cellular life were autotrophs that relied upon inorganic substrates as an energy source and lived at alkaline hydrothermal vents or acidic geothermal ponds.<ref>{{Cite journal |last1=Muchowska |first1=K. B. |last2=Varma |first2=S. J. |last3=Chevallot-Beroux |first3=E. |last4=Lethuillier-Karl |first4=L. |last5=Li |first5=G. |last6=Moran |first6=J. |date=October 2, 2017 |title=Metals promote sequences of the reverse Krebs cycle. |journal=Nature Ecology & Evolution |volume=1 |issue=11 |pages=1716–1721 |doi=10.1038/s41559-017-0311-7 |issn=2397-334X |pmid=28970480|pmc=5659384 |bibcode=2017NatEE...1.1716M }}</ref> Simple biomolecules transported from space was considered to have been either too reduced to have been fermented or too heterogeneous to support microbial growth.<ref>{{Cite journal |last1=Weiss |first1=Madeline C. |last2=Preiner |first2=Martina |last3=Xavier |first3=Joana C. |last4=Zimorski |first4=Verena |last5=Martin |first5=William F. |date=2018-08-16 |title=The last universal common ancestor between ancient Earth chemistry and the onset of genetics |journal=PLOS Genetics |language=en |volume=14 |issue=8 |pages=e1007518 |doi=10.1371/journal.pgen.1007518 |pmid=30114187 |pmc=6095482 |s2cid=52019935 |issn=1553-7404 |doi-access=free }}</ref> Heterotrophic microbes likely originated at low H<sub>2</sub> partial pressures. Bases, amino acids, and ribose are considered to be the first fermentation substrates.<ref>{{Cite journal |last1=Schönheit |first1=Peter |last2=Buckel |first2=Wolfgang |last3=Martin |first3=William F. |date=2016-01-01 |title=On the Origin of Heterotrophy |url=https://www.sciencedirect.com/science/article/pii/S0966842X15002292 |journal=Trends in Microbiology |language=en |volume=24 |issue=1 |pages=12–25 |doi=10.1016/j.tim.2015.10.003 |pmid=26578093 |issn=0966-842X}}</ref>

Heterotrophs are currently found in each domain of life: [[Bacteria]], [[Archaea]], and [[Eukarya]].<ref name=":3">{{Cite book |last1=Kim |first1=Byung Hong |url=http://dx.doi.org/10.1017/9781316761625 |title=Prokaryotic Metabolism and Physiology |last2=Gadd |first2=Geoffrey Michael |date=2019-05-04 |publisher=Cambridge University Press |doi=10.1017/9781316761625 |isbn=978-1-316-76162-5|s2cid=165100369 }}</ref> Domain Bacteria includes a variety of metabolic activity including photoheterotrophs, chemoheterotrophs, organotrophs, and heterolithotrophs.<ref name=":3" /> Within Domain Eukarya, kingdoms [[Fungus|Fungi]] and [[Animal]]ia are entirely heterotrophic, though most fungi absorb nutrients through their environment.<ref name=":4">{{Citation |last1=Taylor |first1=D. L. |title=Mycorrhizal Specificity and Function in Myco-heterotrophic Plants |date=2002 |url=http://dx.doi.org/10.1007/978-3-540-38364-2_15 |pages=375–413 |place=Berlin, Heidelberg |publisher=Springer Berlin Heidelberg |isbn=978-3-540-00204-8 |access-date=2022-04-23 |last2=Bruns |first2=T. D. |last3=Leake |first3=J. R. |last4=Read |first4=D. J.|series=Ecological Studies |volume=157 |doi=10.1007/978-3-540-38364-2_15 }}</ref><ref>{{Cite journal |last=Butterfield |first=Nicholas J. |date=2011 |title=Animals and the invention of the Phanerozoic Earth system |url=http://dx.doi.org/10.1016/j.tree.2010.11.012 |journal=Trends in Ecology & Evolution |volume=26 |issue=2 |pages=81–87 |doi=10.1016/j.tree.2010.11.012 |pmid=21190752 |bibcode=2011TEcoE..26...81B |issn=0169-5347}}</ref> Most organisms within Kingdom [[Protist]]a are heterotrophic while Kingdom [[Plant]]ae is almost entirely autotrophic, except for [[Myco-heterotrophy|myco-heterotrophic]] plants.<ref name=":4" /> Lastly, Domain Archaea varies immensely in metabolic functions and contains many methods of heterotrophy.<ref name=":3" />