Biology:Assembly theory
Assembly theory is a hypothesis that characterizes object complexity. When applied to molecule complexity, its authors claim it to be the first technique that is experimentally verifiable, unlike other molecular complexity algorithms that lack experimental measure.[1] This theory suggests that evolution abides to well defined physical laws, conceptualising objects not as point particles, but as entities defined by their possible formation histories. Thus introducing an assembly index (A), capturing the degree of causation required to produce a given ensemble of objects. [2] The theory was developed as a means to detect evidence of extraterrestrial life from data gathered by astronomical observations or probes.[3]
Background
The hypothesis was proposed by chemist Leroy Cronin in 2017 and developed by the team he leads at the University of Glasgow,[4][5][6] then extended in collaboration with a team at Arizona State University led by astrobiologist Sara Imari Walker, in a paper released in 2021.[7][8] It is difficult to identify chemical signatures that are unique to life.[6][9] For example, the Viking lander biological experiments detected molecules that could be explained by either living or natural non-living processes.[6][10][11]
Assembly theory outputs how complex a given object is as a function of the number of independent parts and their abundances. To calculate how complex an item is, it is recursively divided into its component parts. The 'assembly index' is defined as the shortest path to put the object back together:[1]
[math]\displaystyle{ A=\mathop{\sum }\limits_{i=1}^{N}{e}^{{a}_{i}}\left(\frac{{n}_{i}-1}{{N}_{{\rm{T}}}}\right) }[/math]
Where [math]\displaystyle{ A }[/math] is the assembly of the ensemble, [math]\displaystyle{ a_i }[/math] is the assembly index of object [math]\displaystyle{ i }[/math], [math]\displaystyle{ n_i }[/math] is the object's copy number, [math]\displaystyle{ N }[/math] is the total number of unique objects, [math]\displaystyle{ e }[/math] is Euler's number, and [math]\displaystyle{ N_T }[/math] is the total number of objects in the ensemble.[2]
For example, the word 'abracadabra' contains 5 unique letters (a, b, c, d and r) and is 11 symbols long. It can be assembled from its constituents as a + b --> ab + r --> abr + a --> abra + c --> abrac + a --> abraca + d --> abracad + abra --> abracadabra, because 'abra' was already constructed at an earlier stage. Because this requires 7 steps, the assembly index is 7. The string ‘abcdefghijk’ has no repeats so has an assembly index of 10.
While other approaches can provide a measure of complexity, the researchers claim that assembly theory's molecular assembly number is the first to be measurable experimentally. They argue that the molecular assembly number can be used to gauge the improbability that a complex molecule was created without life, with a higher number of steps corresponding to a higher improbability.[6] This method could be implemented in a fragmentation tandem mass spectrometry instrument to search for biosignatures.[6] Cronin stated "Our system is the first falsifiable hypothesis for life detection and is based on the idea that only living systems can produce complex molecules that could not form randomly in any abundance, and this allows us to sidestep the problem of defining life."[7]
The theory was extended to map chemical space with molecular assembly trees. These trees were formed by arranging constituent pieces in size order. When two or more molecules have common units, their trees are combined, including the two target molecules and various hybrids.[12][4]
The theory was described in detail as a framework that does not alter the laws of physics, but redefines the concept of an ‘object’ on which these laws act. Assembly Theory (AT) conceptualizes objects not as point particles, but as entities defined by their possible formation histories. This allows objects to show evidence of selection, within well-defined boundaries of individuals or selected units. A measure is introduced called assembly (A), capturing the degree of causation required to produce a given ensemble of objects. This approach means it is possible to incorporate novelty generation and selection into the physics of complex objects. It explains how these objects can be characterized through a forward dynamical process considering their assembly. By reimagining the concept of matter within assembly spaces, AT provides a powerful interface between physics and biology. It discloses a new aspect of physics emerging at the chemical scale, whereby history and causal contingency influence what exists.[13]
See also
References
- ↑ 1.0 1.1 "Identifying molecules as biosignatures with assembly theory and mass spectrometry". Nature Communications 12 (3033): 3033. 24 May 2021. doi:10.1038/s41467-021-23258-x. PMID 34031398. Bibcode: 2021NatCo..12.3033M.
- ↑ 2.0 2.1 Sharma, Abhishek; Czégel, Dániel; Lachmann, Michael; Kempes, Christopher P.; Walker, Sara I.; Cronin, Leroy (October 2023). "Assembly theory explains and quantifies selection and evolution" (in en). Nature 622 (7982): 321–328. doi:10.1038/s41586-023-06600-9. ISSN 1476-4687. PMC 10567559. Bibcode: 2023Natur.622..321S. https://www.nature.com/articles/s41586-023-06600-9.
- ↑ Smith, Adam (25 May 2021). "Scientists create 'life detection' tool help hunt down alien life". The Independent. https://www.independent.co.uk/life-style/gadgets-and-tech/alien-life-molecule-assembly-theory-b1853340.html.
- ↑ 4.0 4.1 Welter, Kira (13 October 2021). "Exploiting evolution to explore chemical space shows promise for drug discovery". Chemistry World. Royal Society of Chemistry. https://www.chemistryworld.com/news/exploiting-evolution-to-explore-chemical-space-shows-promise-for-drug-discovery/4014561.article.
- ↑ Marshall, Stuart M.; Murray, Alastair R. G.; Cronin, Leroy (2017). "A probabilistic framework for identifying biosignatures using Pathway Complexity". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375 (2109). doi:10.1098/rsta.2016.0342. PMID 29133442. Bibcode: 2017RSPTA.37560342M.
- ↑ 6.0 6.1 6.2 6.3 6.4 "Complex molecules could hold the secret to identifying alien life" (Press release). University of Glasgow. 24 May 2021. Retrieved 2021-07-30.
- ↑ 7.0 7.1 Baptista, Kim (28 May 2021). "Scientists develop new molecular tool to detect alien life" (Press release). Arizona State University.
- ↑ Sara Imari Walker; Leroy Cronin; Alexa Drew; Shawn Domagal-Goldman; Theresa Fisher; Michael Line; Camerian Millsaps (7 April 2019). "Probabilistic Biosignature Frameworks". Planetary Astrobiology. doi:10.2458/azu_uapress_9780816540068-ch018. https://books.google.com/books?id=x8fcDwAAQBAJ&pg=PA477.
- ↑ Schwieterman, Edward W.; Kiang, Nancy Y.; Parenteau, Mary N.; Harman, Chester E.; Dassarma, Shiladitya; Fisher, Theresa M.; Arney, Giada N.; Hartnett, Hilairy E. et al. (2018). "Exoplanet Biosignatures: A Review of Remotely Detectable Signs of Life". Astrobiology 18 (6): 663–708. doi:10.1089/ast.2017.1729. PMID 29727196. Bibcode: 2018AsBio..18..663S.
- ↑ NASA Astrobiology (2 September 2021). Universal Life Detection: Astrobiology & Assembly Theory. YouTube.
- ↑ Plaxco, Kevin W.; Gross, Michael (2011-08-12). Astrobiology: A Brief Introduction. JHU Press. pp. 285–286. ISBN 978-1-4214-0194-2. https://books.google.com/books?id=x83omgI5pGQC&pg=PA285. Retrieved 2013-07-16.
- ↑ Liu, Yu; Mathis, Cole; Bajczyk, Michał Dariusz; Marshall, Stuart M.; Wilbraham, Liam; Cronin, Leroy (2021). "Exploring and mapping chemical space with molecular assembly trees". Science Advances 7 (39): eabj2465. doi:10.1126/sciadv.abj2465. PMID 34559562. Bibcode: 2021SciA....7J2465L.
- ↑ Sharma, Abhishek; Czégel, Dániel; Lachmann, Michael; Kempes, Christopher P.; Walker, Sara I.; Cronin, Leroy (October 2023). "Assembly theory explains and quantifies selection and evolution" (in en). Nature 622 (7982): 321–328. doi:10.1038/s41586-023-06600-9. ISSN 1476-4687. PMC 10567559. Bibcode: 2023Natur.622..321S. https://www.nature.com/articles/s41586-023-06600-9.
Further reading
| Library resources about Assembly theory |
- Cronin, Leroy; Walker, Sara Imari (2016-06-03). "Beyond prebiotic chemistry" (in en). Science 352 (6290): 1174–1175. doi:10.1126/science.aaf6310. ISSN 0036-8075. PMID 27257242. Bibcode: 2016Sci...352.1174C. https://www.science.org/doi/10.1126/science.aaf6310.
- Cronin, Leroy; Krasnogor, Natalio; Davis, Benjamin G.; Alexander, Cameron; Robertson, Neil; Steinke, Joachim H. G.; Schroeder, Sven L. M.; Khlobystov, Andrei N. et al. (2006). "The imitation game—a computational chemical approach to recognizing life" (in en). Nature Biotechnology 24 (10): 1203–1206. doi:10.1038/nbt1006-1203. ISSN 1546-1696. PMID 17033651. https://www.nature.com/articles/nbt1006-1203.
- Ball, Philip (4 May 2023). "A New Theory for the Assembly of Life in the Universe" (in en). Quanta Magazine. https://www.quantamagazine.org/a-new-theory-for-the-assembly-of-life-in-the-universe-20230504/.
External links
- Finding Life by Looking for Complexity: Interview with Leroy Cronin about assembly theory on Planetary Radio broadcast, 30 June 2021.
- Lee Cronin: Origin of Life, Aliens, Complexity, and Consciousness: Interview with Leroy Cronin in which assembly theory is discussed (starting at 1:27:23) on the Lex Fridman Podcast.
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