Evolution

• Mutation is the ultimate source of genetic variation in a population.
• Panspermia:

  • Claim: Comets may have brought life to Earth
  • Evidence: Bacteria survived a powerful impact on granite, similar to a comet hitting Earth's surface
  • Justification: Bacteria's ability to survive powerful impacts suggests that the first living organisms on Earth could have come from outer space
• Biogenesis (Pasteur’s experiment):

  • Claim: Life stems from life
  • Evidence: Broth in the swan neck flask remained unchanged, while the open flask showed microbial growth from the outside environment
  • Justification: Microbial growth in the broth was caused by microbes entering from the outside environment, supporting the claim that life must stem from life
• Chemical Evolution (proposed by Haldane and Oparin and tested by Miller and Urey):

  • Claim: Life can rise from chemical reactions
  • Evidence: Stanley Miller simulated early Earth conditions in a lab, producing amino acids from methane, hydrogen, and ammonia
  • Justification: Production of amino acids under ancient Earth-like conditions through simple chemical reactions supports the claim that ancient molecules of life could have formed chemically
• RNA World Hypothesis:

  • Claim: RNA came before DNA and protein
  • Evidence: RNA can self-replicate and synthesize materials, some RNA mutated into DNA
  • Justification: RNA's ability to perform multiple functions without relying on other molecules suggests it could have been the first to exist, later giving rise to DNA
• Endosymbiotic Theory:

  • Claim: One organism absorbed another and combined abilities
  • Evidence: Chloroplasts and mitochondria have their own DNA, similar to ancient bacteria, and multiply similarly
  • Justification: Similarities in DNA, ribosomes, and cellular membranes between chloroplasts, mitochondria, and ancient bacteria support the theory that these organelles underwent endosymbiosis to exist within different organisms today
• Evolutionary change is based on the interactions between populations & their environment, resulting in adaptations (inherited characteristics) to increase fitness
• Descent with modification is the change over time in the genetic composition of a population from generation to generation
• Two different ways to view evolution:

  • Pattern: revealed by data from many scientific disciplines, showing that life has evolved over time
  • Process: consists of the mechanisms that cause the observed pattern of change
• Before Darwin:

  • Aristotle viewed species as fixed and unchanging, arranging life forms on a ladder of increasing complexity
  • Carolus Linnaeus classified life's diversity with binomial nomenclature
  • Georges Cuvier developed Paleontology and speculated on catastrophic events in strata boundaries
  • James Hutton proposed geological change is slow and gradual
  • Charles Lyell stated Earth's processes are the same rate in the past and present
  • Jean-Baptiste de Lamarck published a theory of evolution based on use and disuse and inheritance of acquired characteristics
• Charles Darwin:

  • English naturalist who joined the HMS Beagle for a 5-year research voyage around the world in 1831
  • Notable stop at the Galapagos Islands where he observed Darwin's Finch Collection
  • Adaptations are inherited characteristics that enhance survival and reproduction in specific environments
  • Natural selection is a process where individuals with certain inherited traits tend to survive and reproduce at a higher rate
• Darwin's observations and inferences:

  • Members of a population vary in inherited traits
  • All species can produce more offspring than the environment can support
  • Individuals with higher probability of surviving and reproducing tend to have more offspring
  • Unequal ability to survive and reproduce leads to accumulation of favorable traits in the population over generations
• Key features of Natural Selection:

  • Individuals with certain heritable traits survive and reproduce at a higher rate
  • Over time, natural selection can increase the frequency of favorable adaptations
  • Natural selection can result in adaptation to new conditions, sometimes leading to new species
• Important points of Natural Selection:

  • Individuals do not evolve, populations evolve
  • Natural selection can only amplify or diminish heritable traits that differ among individuals
  • Favorable traits vary in different environments
• Key Ideas of Natural Selection:

  • Variation: genetic variation within a population
  • Competition: overproduction of offspring leads to competition for survival
  • Adaptations: individuals with beneficial adaptations are more likely to survive and pass on their genes
  • Selection: change in allele frequency over generations
• Main ideas of Natural Selection:

  • Overproduction of offspring leads to competition for resources
  • Heritable variations exist within a population
  • Individuals with more favorable adaptations are more likely to survive, reproduce, and pass traits to future generations
  • Changes in genetic composition of the population occur over generations
• Evidence for Evolution:

  • Direct observations: insect populations becoming resistant to pesticides, antibiotic-resistant bacteria, peppered moth color change
  • Homology: similarities in related species, homologous structures, analogous structures, embryonic development, vestigial structures, molecular homologies
  • Fossil records: show evolutionary changes over time and the origin of major new groups of organisms
  • Biogeography: geographic distribution of species, endemic species, continental drift, and Pangaea
• Taxonomy (classification) was proposed by Carolus Linnaeus
• Binomial nomenclature consists of Genus and species
• Taxa broader than the genus are not italicized, though they are capitalized
• The hierarchy of classification in the Linnaean system is: Domain - Kingdom - Phylum - Class - Order - Family - Genus - Species
• Classification is based on anatomy & morphology, using physical characteristics
• Scientists have difficulty determining the evolutionary relationships of organisms through their classification in the Linnaean system
• Domains in the Tree of Life are Bacteria, Archaea, and Eukarya
• Common Ancestry of All Life Forms includes elements conserved across all 3 domains: DNA and RNA as carriers of genetic info, universal genetic code (codon → amino acids), conserved metabolic pathways
• Phylogenetics focuses on the evolutionary history of organisms
• Tools used to determine evolutionary relationships include fossils, morphology (homologous structures), and molecular evidence (DNA, amino acids)
• A Phylogenetic Tree is a branching diagram showing the evolutionary history of a group of organisms, where branch lengths can indicate time and genetic changes
• Constructing phylogenetic trees involves considering divergent vs. convergent evolution, homologous structures, and analogous structures
• A Cladogram is a diagram depicting patterns of shared characteristics among groups, with a Clade being a group of species that includes an ancestral species + all descendants
• Shared derived characteristics (evolutionary novelties) are used to construct cladograms
• Horizontal (Lateral) gene transfer involves the movement of genes between different domains, including the exchange of transposable elements, plasmids, viral infections, and fusion of organisms
• Phylogenetic trees are hypotheses subject to change based on available data, presenting a hypothesis about evolutionary relationships
• The order of taxa on the right side of a tree does not represent a sequence of evolution, but patterns of descent
• The ages of taxa or branch points shown in a tree cannot be inferred, and assumptions should not be made about when a species evolved or how much change occurred in each lineage
• The Principle of maximum parsimony suggests using the simplest explanation (fewest DNA changes) to construct phylogenetic trees
• Cladistics is a set of methods for inferring phylogeny from homologous characters, primarily using common ancestry to classify organisms
• Molecular clocks measure evolutionary change based on regions of the genome that appear to evolve at constant rates, estimating the date of past evolutionary events
• The rates of evolution may be irregular for different species, depending on the importance of genes where important genes lead to slower evolution due to harmful changes in amino acid sequences
• The smallest unit of evolution is a population