A4.1

• Evolution


  Change in the heritable characteristics of a population
• Evolution occurs by the mechanism of natural selection proposed by Charles Darwin
• Lamarck's theory of evolution

  Individuals in a population could change their phenotype based on need and then pass this trait to offspring
• Darwin's theory of evolution is different from Lamarck's theory
• The theory of evolution by natural selection predicts and explains a broad range of observations and is unlikely ever to be falsified
• The nature of science makes it impossible to formally prove that the theory of evolution is true by correspondence
• The theory of evolution is referred to as a theory, despite all the supporting evidence
• Evidence for evolution from base sequences in DNA or RNA and amino acid sequences in proteins


  Sequence data gives powerful evidence of common ancestry
• Evidence for evolution from selective breeding of domesticated animals and crop plants

  Variation between different domesticated animal breeds and varieties of crop plant, and between them and the original wild species, shows how rapidly evolutionary changes can occur
• Evidence for evolution from homologous structures

  Structures that occupy similar positions in the organism, have a common basic structure but may have evolved different functions
• Convergent evolution


  The origin of analogous structures, which have the same function but different evolutionary origins
• Speciation by splitting of pre-existing species

  The only way in which new species have appeared, which increases the total number of species on Earth
• Roles of reproductive isolation and differential selection in speciation

  Geographical isolation as a means of achieving reproductive isolation, and the separation of bonobos and common chimpanzees by the Congo River as a specific example of divergence due to differential selection
• Sympatric and allopatric speciation


  Reproductive isolation can be geographic, behavioural or temporal
• Adaptive radiation


  Allows closely related species to coexist without competing, thereby increasing biodiversity in ecosystems where there are vacant niches
• Barriers to hybridization and sterility of interspecific hybrids

  Courtship behaviour often prevents hybridization in animal species, and a mule is an example of a sterile hybrid
• Abrupt speciation in plants by hybridization and polyploidy

  Use knotweed or smartweed (genus Persicaria) as an example because it contains many species that have been formed by these processes
• When referring to organisms in an examination, either the common name or the scientific name is acceptable
• Lamarck proposed that individuals in a population could change their phenotype based on need and then pass this trait to offspring
• All living organisms use the same DNA and RNA code
• Similarities in base sequences of DNA

  Provide evidence for evolution, suggesting a common ancestor
• Species sharing a greater proportion of DNA


  Are more closely related
• Species showing more differences in their DNA

  Are more distantly related
• Ubiquitous proteins


  Those found in all species which makes them useful for comparison
• Cytochrome c protein


  An example of a ubiquitous protein
• The greater the differences in the amino acid sequence, the further back the common ancestor was and the less closely related the species are
• The biochemical processes of producing proteins including reading the DNA/RNA is also universal indicating a common universal ancestor (LUCA)
• Selective breeding (also called artificial selection)


  The process by which humans breed animals and plants for particular traits
• Examples of selective breeding


  • Breeding dogs for herding, e.g. sheepdogs or racing, e.g. greyhounds
  • Cows are bred for milk yield or meat
  • Crops have been bred for increased yield and/or disease resistance – e.g. wheat, barley, oats and rice
• Homologous structures


  Structures that occupy similar positions in the organism, have a common basic structure but may have evolved different functions
• The pentadactyl limb in vertebrates is an example of a homologous structure</b>
• Adaptive radiation


  Results in diversification of an ancestral species increasing biodiversity
• Vestigial organs


  Organs of reduced size that appear to have no apparent function in one species but are present and functional in other species
• Examples of vestigial organs in humans

  • Appendix, coccyx, abdominal separation (which forms the 6 pack), muscles to wriggle ears, body hair
• Vestigial organs suggest a common ancestor with a well-developed version of the vestigial organ
• Fossil evidence


  The preserved remains or traces of any organism from the remote past
• Direct (body) fossils


  Bones, teeth, shells, leaves, etc.
• Indirect (trace) fossils


  Footprints, tooth marks, tracks, burrows, etc.
• Fossil record


  The sum of all discovered and undiscovered fossils and their relative placement in rock, which provides the dimension of time to the study of evolution
• Fossil evidence may be one of two types: Direct (body fossils) such as bones, teeth, shells, leaves, etc.