Biological Sciences
Last Universal Common Ancestor
The Last Universal Common Ancestor (LUCA) is the hypothetical organism that is believed to be the common ancestor of all life on Earth. It is thought to have existed around 3.5 to 4 billion years ago and was likely a single-celled organism that lived in a hydrothermal vent or a similar environment. LUCA is an important concept in evolutionary biology and helps scientists understand the origins of life on Earth.
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eBook - ePubTheistic Evolution
A Scientific, Philosophical, and Theological Critique
- J. P. Moreland, Stephen C. Meyer, Christopher Shaw, Ann K. Gauger, Wayne Grudem, J. P. Moreland, Stephen C. Meyer, Christopher Shaw, Ann K. Gauger, Wayne Grudem(Authors)
- 2017(Publication Date)
- Crossway(Publisher)
TABLE 12.1. Matrix of opinion showing natural historians and biologists holding the four possible positions concerning universal common descent (UCD) and intelligent design. Left upper quadrant: the Last Universal Common Ancestor (LUCA) existed at the root of a single tree of life (TOL), and no intelligent design (ID) occurred. Right upper quadrant: LUCA did not exist, and no ID occurred. Left lower quadrant: LUCA and TOL existed and ID occurred. Right lower quadrant: LUCA and TOL did not exist and ID occurred.Given these points, and the range of positions on offer, the reader may be wondering, “Well, if UCD is endorsed by some intelligent design theorists, and if UCD and materialism are independent of each other, why bother challenging UCD, or CD, at all? Wouldn’t the wiser course be to withhold judgment about the theory, at least provisionally, since most biologists still accept UCD?”Perhaps—but we think the wisest course is to pursue the truth. Here is the only question about UCD ultimately worth asking: Is the theory true ? If UCD is true, then Christians—indeed, everyone—will have to make their peace with it. If UCD isn’t true, however, then no one, Christians included, should hang on to the theory.To begin, we should examine how evolutionary biologists normally infer that two or more species share a common ancestor. This will provide the terms and concepts we shall use throughout the remainder of the chapter.The Anatomy of Inferences to Common AncestryRichard Dawkins says many things that are beautifully clear—wrong, maybe, but nonetheless clear and easy to follow. In The Blind Watchmaker , Dawkins explains why he thinks all organisms share a common ancestor:. . . it is a fact of great significance that every living thing, no matter how different from others in external appearance it may be, ‘speaks’ almost exactly the same language at the level of the genes. The genetic code is universal. I regard this as near -conclusive proof that all organisms are descended from a single common ancestor. The odds of the same dictionary of arbitrary ‘meanings’ arising twice are almost unimaginably small.7
eBook - PDF- J. Tze-Fei Wong, Antonio Lazcano(Authors)
- 2009(Publication Date)
- CRC Press(Publisher)
CHAPTER 15 Root of Life J. Tze-Fei Wong* 15.1 Introduction T he usage of the universal genetic code basically by all living organisms with only minor variations points to the descent of all living species from a Last Universal Common Ancestor, or LUCA, at the root of the tree oflife. Knowledge ofthe nature of LUCA is pivotal to understanding the pathways that gave rise to LUCA, as well as the pathways that led from LUCA to present day life. An important method for finding the root oflife is based on the sequences of protein paralogs , namely sister sequences which stem from a duplication of the same gene but end up serving different biochemical functions. These sister sequences were nearly identical at the start. As time went on, they diverged more and more and the extent of their divergence measures how far they have moved away from one another. The first attempts at using mutual rootings of paralogous protein trees to search for LUCA located the root oflife in the Bacteria domain of the small subunit ribosomal RNA (SSU rRNA) tree (Section 2.4). However, there were at first very few avail able protein paralog sequences from all three biological domains and it was also not known at the time that the paralogous rooting method is fraught with artifacts such as long branch attraction, horizontal gene transfer and mutational saturation that could readily invalidate rootings based on just a few species.5,6The initial paralogous rooting of the ValRS-IleRS trees,7for example, does not contain enough species to detect any of the artifacts now known from an extensive study* to heavily beset the IleRS tree. As a result, the early paralogous rootings in the Bacteria domain are unreliable and the unreliability has given rise to pessimism questioning whether the root will ever be found.9,10 15.2 Transfer RNA W ith the search for LUCA based on protein paralogs troubled by artifacts, other biopolymers have to be looked to for sequence information.
eBook - ePub- Jana Švorcová, Anton Markoš(Authors)
- 2019(Publication Date)
- CRC Press(Publisher)
Volvox; Chen et al. 2014). Yet later came enigmatic 2D fossils known as fauna Ediacara (McMennamin and McMennamin 1990, Yuan et al. 2011). It is not surprising that some authors claim that all three branches of life may be of similar age (Glanssdorf et al. 2008); later we will press this point as ours, too.To illustrate the difficulties our quest inheres, take the contemporary biosphere. For example, the rich world of picoplankton, tiny eukaryotes (picoplankton under 1 μm—smaller than most bacteria) flourishing in oceans, was never expected and till recently never sought (Massana 2011, Seenivasan et al. 2013). Moreover, these creatures often enter symbiosis with cyanobacteria (Thompson et al. 2012); in this same environment, we also find tiny bacteria (under 0.2 μm; Luef et al. 2015), difficult to discover even in contemporary biosphere, and there is no chance that life this small could have left fossils to provide us keys to the early evolution of life.Origins: Biosphere LUCAThe term Last Universal Common Ancestor (LUCA) commonly denotes the hypothetical ancestral population of cells that gave rise to all extant form of life. This much is agreed, if nothing else; as to its basic characteristics, the views differ. Many authors take the view that LUCA belonged to the RNA world. The division of labor between DNA–RNA–protein, the argument goes, took place later (Koonin et al. 2006, Glansdorff et al. 2008), perhaps even after LUCA split into the three extant domains of cellular life (Forterre 2010b). Such scenario supposes that viruses played the role of DNA ‘donors’. We prefer the alternative view, which argues that the biosphere’s LUCA already showed the basic properties typical of contemporary life, as listed in previous chapter: genetic processes and code, metabolism and information processing based in proteins, symbiotic interactions, etc. We also envisage LUCA as a common ancestor of all
eBook - PDFEvolution
The First Four Billion Years
- Michael Ruse, Joseph Travis, Michael Ruse, Joseph Travis(Authors)
- 2011(Publication Date)
- Belknap Press(Publisher)
Molecular Evolution Francisco J. Ayala Molecular biology has made it possible to reconstruct the continuity of suc-cession from the original form of life, ancestral to all living organisms, to every species now living on earth. The universal tree of life, which embraces all known sorts of organisms, includes three sets of branches, Bacteria, Ar-chaea, and Eukarya, which all emerged from one form of life, LUCA (Last Universal Common Ancestor; Figure 1). All living organisms are related by common descent from a single form of life, represented by the tree trunk in the figure. Life may have originated more than once on our planet—we presently do not know—but only one form of life prospered and left descen-dants, the organisms that now populate the earth. Bacteria and Archaea are prokaryotic microscopic organisms. Eukarya are organisms with complex cells that contain several organelles, one of which, the nucleus, includes the hereditary DNA. Most eukaryotic organisms are single celled and microscopic. Animals, plants, and fungi are multicellular or-ganisms, three of the many branches of the Eukarya set. The main branches of the universal tree of life from LUCA, several billion years ago, to the present have been reconstructed on the whole and in many details. More details about more and more branches are published in scores of scientific articles every month. The virtually unlimited evolutionary infor-mation encoded in the DNA sequence of living organisms allows evolution-ists to reconstruct any evolutionary relationships that have led to present-day organisms, or among them, with as much detail as wanted. Invest the neces-sary resources (time and laboratory expenses), and you can have the answer to any query with as much precision as you want. Molecular Evolution: Uniformity and Diversity In its unveiling of the nature of DNA and the workings of organisms at the level of enzymes and other protein molecules, molecular biology has shown the unity of life.
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