{{technical|date=September 2024}} {{Short description|Possible earliest ancestor of the LUCA ancestral cell}} The '''first universal common ancestor''' ('''FUCA''') is proposed to have been a non-cellular entity that was the earliest organism with a genetic code capable of performing biological translation of RNA molecules to protein formation through peptides synthesis.<ref name=":04">{{Citation |last1=Prosdocimi |first1=Francisco |title=The First Universal Common Ancestor (FUCA) as the Earliest Ancestor of LUCA's (Last UCA) Lineage |date=2019 |work=Evolution, Origin of Life, Concepts and Methods |pages=43–54 |editor-last=Pontarotti |editor-first=Pierre |url=https://www.preprints.org/manuscript/201806.0035/v1/download |access-date=2023-11-02 |archive-url=https://web.archive.org/web/20220629043452/https://www.preprints.org/manuscript/201806.0035/v1/download |archive-date=2022-06-29 |url-status=live |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-030-30363-1_3 |isbn=978-3-030-30363-1 |s2cid=199534387 |last2=José |first2=Marco V. |last3=de Farias |first3=Sávio Torres |url-access=subscription}}</ref><ref name=":32">{{Cite book |last1=Prosdocimi |first1=Francisco |url=https://www.researchgate.net/publication/338753723 |title=From FUCA To LUCA: A Theoretical Analysis on the Common Descent of Gene Families |last2=Farias |first2=Farias |year=2020 |doi=10.31080/ASMI.2020.03.0494 |access-date=2023-11-02 |doi-broken-date=12 July 2025}}</ref> Its descendants would include the last universal common ancestor (LUCA) and, therefore, all modern cells.<ref name=":04" /><ref name=":12">{{Cite journal |last1=Harris |first1=Hugh M. B. |last2=Hill |first2=Colin |date=2021 |title=A Place for Viruses on the Tree of Life |journal=Frontiers in Microbiology |volume=11 |doi=10.3389/fmicb.2020.604048 |issn=1664-302X |pmc=7840587 |pmid=33519747 |doi-access=free}}</ref> FUCA would also be the ancestor of ancient sister lineages of LUCA with no direct modern descendants, but which may have transferred genetic material horizontally into the genomes of early descendants of LUCA.<ref name=":12" />
FUCA is thought to have been composed of progenotes, ancient biological systems that would have used RNA for their genome and self-replication.<ref name=":22">{{Cite journal |last1=de Farias |first1=Sávio Torres |last2=Jose |first2=Marco V. |last3=Prosdocimi |first3=Francisco |year=2021 |title=Is it possible that cells have had more than one origin? |url=https://www.preprints.org/manuscript/202012.0657/v1/download |url-status=live |journal=Bio Systems |volume=202 |bibcode=2021BiSys.20204371D |doi=10.1016/j.biosystems.2021.104371 |issn=1872-8324 |pmid=33524470 |archive-url=https://web.archive.org/web/20231230224025/https://www.preprints.org/manuscript/202012.0657/v1/download |archive-date=2023-12-30 |access-date=2024-02-23 |article-number=104371}}</ref><ref name=":42">{{Cite journal |last=Woese |first=Carl |date=1998-06-09 |title=The universal ancestor |journal=Proceedings of the National Academy of Sciences |language=en |volume=95 |issue=12 |pages=6854–6859 |bibcode=1998PNAS...95.6854W |doi=10.1073/pnas.95.12.6854 |issn=0027-8424 |pmc=22660 |pmid=9618502 |doi-access=free}}</ref><ref name="NLane_Funke2">{{cite book |author-link1=Nick Lane |url=https://archive.org/details/vitalquestionene0000lane |title=The Vital Question – Energy, Evolution, and the Origins of Complex Life |vauthors=Lane N |date=2015 |publisher=WW Norton |isbn=978-0-393-08881-6 |page=[https://archive.org/details/vitalquestionene0000lane/page/77 77] |url-access=registration}}</ref> By comparison, LUCA would have had a complex metabolism and a DNA genome containing hundreds of genes grouped into several gene families.<ref name=":04" />
== Origins == {{see also|Abiogenesis}} Long before compartmentalized biology like FUCA appeared, life is hypothesized to have emerged through the organization of a pre-cellular era in the RNA world.<ref name=":22" /> In this era, self-replicating RNA molecules would have both stored genetic information and catalyzed chemical reactions. Translation machinery and the genetic code is universally present in all known cells and viruses, indicating a single origin for biological systems (monophyly).<ref name=":04" /><ref name=":22" />
FUCA is thought to have been the first organism capable of biological translation, using RNA molecules to convert information into peptides and produce proteins.<ref name=":04" /> This first translation system is thought to have formed at the same time as an error-prone early genetic code.<ref name=":04" /> FUCA would be the first biological system to have a genetic code that dictates specific protein assembly.<ref name=":32" />
The development of FUCA would have been a gradual process initially without the genetic code.<ref name=":04" />{{clarify inline|date=December 2025}} FUCA is hypothesized to have arisen from the ribosome, a complex made of RNA and proteins<ref name=":04" /> that evolved from a more primitive ribonucleoprotein machinery.<ref name=":22" /> FUCA appeared when the early peptidyl transferase center first emerged and when RNA world replicators could bond amino acids into short chained oligopeptides.<ref name=":04" />
The first genes of FUCA most likely encoded ribosomal components, primitive tRNA-aminoacyl transferases, and other proteins that helped stabilize and maintain biological translation.<ref name=":32" /> These random peptides may have bound back to the single strand nucleic acid polymers which increased their stability and the robustness of the system, binding other stabilizing molecules.<ref name=":04" /> When FUCA matured, its genetic code was then completely established.<ref name=":04" />
It has been proposed that FUCA was composed by a population of open-systems, exchanging components and information with the environment, and a population of self-replicating ribonucleoproteins.<ref name=":22" /> The progenote era began when these interaction systems arrived.<ref name=":22" /> These systems reached maturity when self-organization processes resulted in the emergence of a genetic code.<ref name=":22" /> This genetic code was, for the first time, able to organize an ordered interaction between nucleic acids and proteins through the formation of a biological language.<ref name=":22" /> This caused pre-cellular open systems to start to accumulate information and self-organizing, producing the first genomes by the assembling biochemical pathways.<ref name=":22" /> The pathways probably appeared in different progenote populations that independently evolved.<ref name=":22" />
== Progenotes == Progenotes (also called ribocytes or ribocells)<ref name=":022">{{Cite journal |last1=José |first1=Marco V. |last2=Rêgo |first2=Thais Gaudêncio |last3=Farias |first3=Sávio Torres de |date=2015-12-03 |title=A proposal of the proteome before the last universal common ancestor (LUCA) |journal=International Journal of Astrobiology |language=en |volume=15 |issue=1 |pages=27–31 |doi=10.1017/S1473550415000464 |issn=1473-5504 |doi-access=free}}</ref><ref name="Yarus22">{{cite journal |vauthors=Yarus M |year=2002 |title=Primordial genetics: phenotype of the ribocyte |journal=Annual Review of Genetics |volume=36 |pages=125–51 |doi=10.1146/annurev.genet.36.031902.105056 |pmid=12429689}}</ref><ref name="Viruses2">{{cite book |title=Viruses: Essential Agents of Life |vauthors=Forterre P, Krupovic M |year=2012 |isbn=978-94-007-4898-9 |pages=43–60 |chapter=The Origin of Virions and Virocells: The Escape Hypothesis Revisited |doi=10.1007/978-94-007-4899-6_3}}</ref> are open or semi-open biological systems capable of intensely exchanging genetic information, before the existence of cells and LUCA.<ref name=":43">{{Cite journal |last=Woese |first=Carl |date=1998-06-09 |title=The universal ancestor |journal=Proceedings of the National Academy of Sciences |language=en |volume=95 |issue=12 |pages=6854–6859 |bibcode=1998PNAS...95.6854W |doi=10.1073/pnas.95.12.6854 |issn=0027-8424 |pmc=22660 |pmid=9618502 |doi-access=free}}</ref><ref name=":23">{{Cite journal |last1=de Farias |first1=Sávio Torres |last2=Jose |first2=Marco V. |last3=Prosdocimi |first3=Francisco |year=2021 |title=Is it possible that cells have had more than one origin? |url=https://www.preprints.org/manuscript/202012.0657/v1/download |url-status=live |journal=Bio Systems |volume=202 |bibcode=2021BiSys.20204371D |doi=10.1016/j.biosystems.2021.104371 |issn=1872-8324 |pmid=33524470 |archive-url=https://web.archive.org/web/20231230224025/https://www.preprints.org/manuscript/202012.0657/v1/download |archive-date=2023-12-30 |access-date=2024-02-23 |article-number=104371}}</ref> The term progenote was coined by Carl Woese in 1977,<ref name=":43" /> around the time he introduced the concept of the three domains of life (bacteria, archaea, and eukaryotes). Woese also proposed that each domain originated from a different progenote.<ref name=":23" /><ref>{{Cite journal |last=Koonin |first=Eugene V |date=2014-03-01 |title=Carl Woese's vision of cellular evolution and the domains of life |journal=RNA Biology |volume=11 |issue=3 |pages=197–204 |doi=10.4161/rna.27673 |issn=1547-6286 |pmc=4008548 |pmid=24572480}}</ref> The meaning of progenote changed over time, when in the 1980s, Doolittle and Darnell used the term to refer to the single ancestor of all three domains of life,<ref>{{Cite journal |last1=Doolittle |first1=W. F. |last2=Darnell |first2=J. E. |date=1986-03-01 |title=Speculations on the early course of evolution |journal=Proceedings of the National Academy of Sciences |language=en |volume=83 |issue=5 |pages=1271–1275 |bibcode=1986PNAS...83.1271D |doi=10.1073/pnas.83.5.1271 |issn=1091-6490 |pmc=323057 |pmid=2419905 |doi-access=free}}</ref> now referred to as the last universal common ancestor (LUCA).'''<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 |volume=14 |issue=8 |doi=10.1371/journal.pgen.1007518 |issn=1553-7390 |pmc=6095482 |pmid=30114187 |doi-access=free |article-number=e1007518}}</ref>'''
The terms ribocyte and ribocell refer to progenotes as early forms of ribosomes (protoribosomes), hypothetical primitive cellular organisms with self-replicating RNA<ref name="Yarus22" /><ref name="Viruses2" /> with an RNA genome instead of the usual DNA genome.<ref name="NLane_Funke3">{{cite book |author-link1=Nick Lane |url=https://archive.org/details/vitalquestionene0000lane |title=The Vital Question – Energy, Evolution, and the Origins of Complex Life |vauthors=Lane N |date=2015 |publisher=WW Norton |isbn=978-0-393-08881-6 |page=[https://archive.org/details/vitalquestionene0000lane/page/77 77] |url-access=registration}}</ref> In Carl Woese's Darwinian threshold period of cellular evolution, progenotes are also thought to have had RNA rather than DNA as informational molecule.<ref name=":022" />
The evolution of the ribosome from ancient ribocytes, the self-replicating RNA systems and machinery, into its current form as a translation machine may have been the selective pressure to then incorporate proteins into the ribosome's self-replicating mechanisms, which would increase its capacity to self-replicate.<ref name="NLane_Funke3" /><ref>{{cite journal |vauthors=Fox GE |date=September 2010 |title=Origin and Evolution of the Ribosome |journal=Cold Spring Harb Perspect Biol |volume=2 |issue=9 |doi=10.1101/cshperspect.a003483 |pmc=2926754 |pmid=20534711 |doi-access=free |article-number=a003483}}</ref> Ribosomal RNA is thought to have emerged before cells or viruses, during the time when progenotes existed.<ref name=":22" />
Progenotes both composed FUCA and descended from FUCA. <ref name=":25">{{Cite journal |last1=de Farias |first1=Sávio Torres |last2=Jose |first2=Marco V. |last3=Prosdocimi |first3=Francisco |year=2021 |title=Is it possible that cells have had more than one origin? |url=https://www.preprints.org/manuscript/202012.0657/v1/download |url-status=live |journal=Bio Systems |volume=202 |bibcode=2021BiSys.20204371D |doi=10.1016/j.biosystems.2021.104371 |issn=1872-8324 |pmid=33524470 |archive-url=https://web.archive.org/web/20231230224025/https://www.preprints.org/manuscript/202012.0657/v1/download |archive-date=2023-12-30 |access-date=2024-02-23 |article-number=104371}}</ref> FUCA is thought to have organized the transition from initial biological systems to mature progenotes.<ref name=":25" /> Progenotes were the dominant forms during the Progenote age, when biological systems first originated and assembled.<ref name=":25" /> The Progenote age would have happened after the pre-biotic RNA-world and Peptide-world ages, but before the emergence and presence of organisms and mature biological systems like viruses, bacteria and archaea.<ref name=":25" />
The most successful progenotes populations were probably the ones capable of binding and processing carbohydrates, amino acids, and other intermediated metabolites and co-factors.<ref name=":22" /> In progenotes, there was not complete compartmentalization by membranes and translation of proteins was not precise. Not every progenote had a full metabolism on its own; different metabolic steps occurred in different progenotes. Therefore, it is assumed that there was a community of interacting sub-systems that began to cooperate collectively and eventually culminated in the LUCA.<ref name=":022" />
=== Ribocytes and viruses === {{Main article|Virus World hypothesis}} In the eocyte hypothesis linking the closest known archaeal relatives of eukaryotes (achaean eocytes), the organism at the root of the eocytes lineage may have been a ribocyte from the RNA-world. For cellular DNA and DNA processing systems, an "out of virus" scenario has been proposed. In this model, DNA as the main genetic information material may have first evolved in viruses and was later transferred to ribocytes twice: once transforming them into bacteria and once transforming them into archaea.<ref name="Viruses2" />
Similarly in viral eukaryogenesis, a hypothesis theorizing that eukaryotes evolved from a DNA virus, ribocytes may have been an ancient host for a DNA virus.<ref name="jean2">{{cite journal |last=Claverie |first=Jean-Michel |year=2006 |title=Viruses take center stage in cellular evolution |journal=Genome Biology |volume=7 |issue=6 |page=110 |doi=10.1186/gb-2006-7-6-110 |pmc=1779534 |pmid=16787527 |doi-access=free}}</ref> Because ribocytes used RNA to store their genetic information,<ref name="jean2" /> viruses may initially have used DNA as a way to resist RNA-degrading enzymes present in the host ribocells. The introduction of a DNA-based system may have been as significant for protocells as later additions of chloroplasts or mitochondria through endosymbiosis in evolving eukaryotic cells. In this hypothesis, bacteria, archaea, and eukaryotes each obtained their DNA informational system from a different virus.<ref name="pnas2">{{cite journal |last=Forterre |first=Patrick |date=March 2006 |title=Three RNA cells for ribosomal lineages and three DNA viruses to replicate their genomes: a hypothesis for the origin of cellular domain |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=103 |issue=10 |pages=3669–74 |bibcode=2006PNAS..103.3669F |doi=10.1073/pnas.0510333103 |jstor=30048645 |pmc=1450140 |pmid=16505372 |doi-access=free}}</ref>
In the reduction hypothesis, where giant viruses evolved from primordial cells that became parasitic, viruses might have evolved after FUCA but before LUCA.<ref name=":22" />
== See also == * Abiogenesis * Alternative abiogenesis scenarios * Earliest known life forms * RNP world * Protocell * Pre-cell * Proto-metabolism, that FUCA may or may not have had{{Citation needed|date=May 2026}} * Horizontal gene transfer in evolution
== References == <references />
Category:Origin of life Category:Hypothetical life forms Category:Evolutionary biology Category:Genetic genealogy Category:Events in biological evolution Category:Phylogenetics