Four Unifying Themes of Biology

Four Unifying Themes of Biology

• Diversity of Life and Evolutionary Change: incredible diversity of living things on earth, with three domains: Eubacteria, Archaea, and Eukarya (comprised of four kingdoms: Protista, Plantae, Fungi, and Animalia)
• All evolved from a common ancestral form through evolution
• Evolutionary conservation: all living things descended from a simple cellular creature that existed about 2.5 billion years ago
• Characteristics of common ancestors are preserved in subsequent life forms
• Protein classes are conserved even between kingdoms

Evolution

• Evolution is a unifying theme in biology that connects all levels of biological organization
• Evolution involves genes, proteins, organisms, populations, biotic community, and ecosystem

Origin of Life

• Miller's experiment in 1953: a mixture of H2, CH4, NH3, and H2O was exposed to high electric discharge, resulting in a gaseous phase of advanced molecules and a liquid condensate phase, including amino acids and other organic molecules
• Certain compounds that favored molecular evolution survived, while compounds disfavoring it were destroyed by predator molecules
• The culmination of chemical evolution was the polymerization of monomers, resulting in biopolymers like proteins, polysaccharides, lipids, and polynucleotides
• Certain polymers like histones and protamines are positively charged and protected polynucleotides from predator molecules

Darwin and Evolution

• Charles Darwin was influenced by others, including Malthus, who wrote "Essay on the Principle of Population" in 1798
• Darwin hypothesized natural selection as a means of selective survival of individuals with superior attributes, gradually changing the average characters of the population over many generations
• Additional evidence supporting Darwin's theory includes molecular biology, development, and comparative embryology
• In the 18th and 19th centuries, scientists began to overturn commonly held beliefs, including the idea that the earth was only about 6,000 years old and that all species were created separately and unchanging

Darwin's Life and Work

• Charles Darwin (1809-1882) was the first individual to explain organic evolution in detail
• Darwin joined a five-year sea voyage on the HMS Beagle and collected flora and fauna from many continents and islands
• During the voyage, Darwin noted unexpected patterns among fossils and living organisms, which helped him develop his theory of evolution
• Darwin published his theory in 1859 in his book "Origin of Species"

Darwin's Theory of Evolution

• Darwin argued that natural selection is the main cause of the origin of new species
• The presentation of Darwin's theory was based on the following facts:
  • Overproduction: organisms have the capacity for enormous reproduction
  • Limited environmental resources: the population of each species tends to increase in a geometric ratio but remains almost constant
  • Struggle for existence: to check the increase in the number of each species, there is a struggle for existence, which may be intraspecific, interspecific, and environmental