Scholars Crossing Faculty Publications and Presentations Department of Biology and Chemistry 2000 Theories of the Origin and Early Evolution of Life David A. DeWitt Liberty University, [email protected] Follow this and additional works at: https://digitalcommons.liberty.edu/bio_chem_fac_pubs Part of the Biology Commons, and the Chemistry Commons Recommended Citation DeWitt, David A., "Theories of the Origin and Early Evolution of Life" (2000). Faculty Publications and Presentations. 93. https://digitalcommons.liberty.edu/bio_chem_fac_pubs/93 This Article is brought to you for free and open access by the Department of Biology and Chemistry at Scholars Crossing. It has been accepted for inclusion in Faculty Publications and Presentations by an authorized administrator of Scholars Crossing. For more information, please contact [email protected]. T tect the animals and their habitats, and to pro­ Further Reading Life mote a sense of stewardship of the environment. Goodall's Roots and Shoots children's program, Books Sciences Fossey, D. Gorillas in the Mist. Boston: Houghton Mifflin, for example, promotes environmental education 1983. 1950-present and compassion toward the Earths living things. Goodall,]. The Chimpanzees of Gombe: Patterns of Behav­ She originally began the program in the hopes of ior. Cambridge: Harvard University Press, 1986. influencing young people in Africa. The pro­ Stone, L. Kinship and Gender. Boulder: Westview Press, gram qUickly spread and now has chapters Harper-Collins, 1997. worldwide. Goodall has also been influential in establishing wildlife sanctuaries in Africa, in­ Periodical Articles cluding one in Congo and another in Uganda. Bower, B. "Monkeys Provide Models of Child Abuse." Sci­ Fossey's research and educational efforts were ence News (23 May 1998): 324. instrumental in gaining governmental protection de Waal , E "Bonobo Sex and SOCiety" SCientific Amelican for mountain gorillas in Rwanda. (March 1995): 82-88. Galdikas, B. "Waiting for Orangutans." Discover (Decem­ These sanctuaries, along with habitat protec­ ber 1994): 100-106. tion and educational efforts, will help ensure that Miller, P. "Crusading for Chimps and Humans ... Jane Goodall." to primatologists can continue study the Great National Geographic (December 1995): 102-129. Apes for years to come, and to learn whether hu­ mans and other primates are as closely related Other behaviorally as they are genetically McCarthy, s. "Jane Goodall: The Hopeful Messenger." http://www.salon.comlpeoplelfeaturel1999/1 0/2 7/rea LESLIE A. MERTZ son! NOTICe:_ T; . may be prot~t 'lis Malena; Theories of the Oriiti\'· (ntle 1~by COPyright and Early Evolution of Life S COde) Overview separated them from non-living things. Wohlers discovery suggested that life forms, like non-liv­ After the theory of spontaneous generation was ing forms, were composed of molecules that obey discredited, only religious explanations were of­ the laws of chemistry and physics. Further, it fered to explain the origin of life. Alexander might be possible to produce other molecules of Oparin (1894-1980), an atheist, suggested that life by experimental or natural means. natural chemical reactions produced biological molecules that came together to form the first liv­ Around the time that Charles Darwin ing thing. Later, Stanley Miller tested this hypoth­ 0809-1882) proposed his theory of evolution esis and produced chemical "building blocks" but by natural selection (1859), two other scientists, not life itself. In spite of much progress, there is RudolfVirchow (1821-1902) and louis Pasteur still no clear consensus on how life originated on (1822-1895) showed that another commonly Earth. Some scientists are even looking to outer held theory was false. Spontaneous generation is space for the origin of life. the term that describes the formation of living things from non-living starting material. Scien­ tists believed that worms, insects, mice, and mi­ Background croscopic organisms simply "arose" from decay­ ing meat, grain, broth, or even dirty underwear. The first scientist to synthesize a molecule nor­ The theory seemed reasonable at the time be­ mally produced by living organisms was Friedrich cause no one had any idea of the compleXity or Wohler (1800-1882). In 1828, he accidentally the multitude of interactive molecules that make made urea by heating ammonium cyanate. This up even the Simplest bacteria. For them, a cell finding helped dispel a theory known as "vital­ was only "protoplasm," not much more compli­ ism," which taught that living things and their cated than gelatin. components possessed a "vital force." At the time, scientists believed that living things consisted of Pasteur and Virchow discredited sponta­ "organic matter" driven by that vital force which neous generation and laid the gr6undwork for SCIENCE AND ITS TIM E 5 VOLUME 7 the biogenic law which asserts that life comes acids are syntheSized, a mixture of right- and only from life.. This principle became a key com­ left-handed molecule,S are produced. However, Life ponent of the cell theory: every cell is made only the left-handed version is found in pro­ Sciences from a pre-existing cell. The implication of their teins. When carbohydrates are produced, many work was that only God could have created the different sugars are made. However, the ribose 1950-present first life that would subsequently reproduce. and deoxyribose found in nucleotides are not Their demonstration was so effective that it vir­ made in appreciable amounts. Polymerization of tually prevented any research on the origin of amino acids into proteins and nucleotides into life for decades. RNA and DNA is also a problem. Even then, these molecules are not liVing-they cannot re­ In the 1920s, a Russian chemist named produce themselves, carry out metabolism, and Alexander Oparin coined the term "primordial lack a boundary soup" and suggested that the building blocks of life could spontaneously form and then coalesce Later, Sydney Fox heated amino acids and together to form the first living cell. In his view, they reacted together to form "proteinoids." Un­ the basic components of cells (lipids, carbohy­ like normal proteins which are linear polymers drates, amino acids) aggregate together, forming of amino acids linked by peptide bonds, the pro­ what he called "coacervates." Presumably, these teinoids were branched polymers with both pep­ coacervates would eventually carry out rudi­ tide and non-peptide bonds. The proteinoids mentary metabolism and some would repro­ could aggregate into microspheres and absorb duce. Oparin also proposed that the atmosphere various molecules. The aggregates were ob­ of the early Earth differed from the present one served to enlarge and split into smaller frag­ by having reducing gases such as hydrogen, ments, although this could hardly be called re­ methane, and ammonia in abundance. The production. British physiologist].B.S. Haldane (1892-1964) As scientists began to unravel how the independently concurred with Oparin, propos­ amino acid sequence of proteins is coded for in ing that oxygen was absent during the origin of DNA and how DNA is replicated, there arose a life because it would have prevented the forma­ paradox. The sequence of amino acids in a pro­ tion of important organic molecules. This as­ tein is not random but determined by the exact sumption about the atmosphere was not based sequence of nucleotides in DNA. Therefore, a on experimental evidence but on an understand­ meaningful DNA sequence is required to pro­ ing of the requirements for producing the de­ duce a functional protein. However, proteins sired molecules. and enzymes are necessary in the replication of Oparin's hypothesis was tested in the early DNA, the transcription of mRNA, and the pro­ 1950s by Stanley Miller, a graduate student in duction of the nucleotides themselves. A con­ Harold Urey's (1893-1981) laboratory, at the ceptual difficulty arose because one could not University of Chicago. Miller designed an appa­ start life with either proteins or DNA since each ratus that would simulate a reducing atmosphere is so dependent on the other. and the presumed conditions of the early Earth. The conundrum was apparently resolved by He used a spark discharge to mimic lightning Walter Gilbert (1932- ), who proposed that life and proVide the energy required for the organic originated in an "RNA world." He suggested that syntheSiS reactions. Millers chamber lacked oxy­ the first living things consisted solely of RNA­ gen because this gas would prevent the forma­ that proteins and DNA were later developments. tion of the desired molecules. In a short time, This was based on the observation that proteins Miller found that the chamber produced 13 of are translated from mRNA with the help of tRNA the 20 amino acids found in proteins. Variations and rRNA. Scientists also found that RNA could of this type of experiment were later shown to be reverse transcribed into DNA, a process car­ produce carbohydrates and the nitrogen-contain­ ried out by the HIV virus. Further, certain RNA ing bases of nucleotides found in DNA and RNA. called ribozymes carry out limited catalytic ac­ The work of Urey and Miller was hailed as pro­ tivities like enzymes. RNA, then, appears to have ducing the "building blocks of life." the perfect combination of features to be the first However, producing such "building blocks" molecules of life. However, the relative instabili­ is not the same as producing life and was not ty: of nucleotides at high temperatures, the lack qualitatively different than Wohler syntheSizing of appreciable ribose, and the inability for RNA urea. Chemical synthesis of bUilding blocks is to replicate itself pose serious problems for this complicated by several factors. When amino hypothesis. Therefore, some scientists are sug- SCIENCE AND ITS TIM E S VOLUME 7 gesting a pre-RNA world that would later give pothesis to explain the origin of organelles, in­ Lift rise to the RNA world. They have proposed clay cluding the mitochondria. According to this view, Sciences to serve in this role.