7.6 The Modern Theory of Evolution

7.6 The Modern Theory of Evolution 


Definitions

  • Radioisotope: an atom with an unstable nucleus that is capable of undergoing radioactive decay

  • Modern evolutionary synthesis: the modern theory of evolution that takes into account all branches of biology 

  • Gene pool: all alleles in a species/population

  • Plate tectonics: the scientific  theory that describes the large-scale movements and features of Earth’s crust

  • Pseudogene: a vestigial gene that no longer codes for a functioning protein, remains of a gene that once served a useful function

  • Evolution: changes ina  species’ gene pool over time 

  • Mutations: changes in DNA sequence, creating new traits

  • Duplication mutations: extra gene copies may evolve new functions

  • Homologous genes: inherited from common ancestors; reveal species’ relatedness

  • Pseudogenes: vestigial, non functional genes due to mutation


Key Advances in Evolutionary Biology

  • Modern genetics explains heredity & variation (source of biological diversity)

  • Fossil records and geology advancements provide strong evidence for evolution

  • Technology improvements enable accurate dating of Earth’s age and fossils


The Age of Earth

  • Pre-20th century belief: Earth <10,000 years old; species unchanged

  • Current understanding: 

    • Earth: 4.5 billion years old

    • Universe: 13 billion years old

    • Supported by geology, physics


Radiometric Dating

  • Uses radioisotpes to date rocks/fossils 

  • Parent isotope decays into daughter isotope at a constant rate

  • Half life: time for 50% of a parent isotope to decay

    • Example: carbon-14 decays into nitrogen-14

  • Accurate, quantitative method for determining geological timelines 


Modern Evolutionary Synthesis 

  • Combines Darwin’s N.S with modern genetics 

  • Variation arises from: 

    • Sexual reproduction (shuffling alleles) 

    • Mutations (new alleles) 


Mutations & variation

  • Different types of mutations; base switches, insertions, deletions, duplications

  • 3 different effects: 

    • Neutral: no effect: occur in non-coding DNA

    • Beneficial: advantageous traits selected for by the environment

    • Harmful: decrease fitness; selected against 


Homologous Genes & Pseudogenes

  • DNA sequence similarity in mammals (cow, whale, hippo) → homologous 

  • Dolphins: loss of olfactory receptor genes due to aquatic lifestyle → pseudogenes

  • Humans: defective GULO gene (vitamin C production) → pseudogenes 


Fossil Evidence and Biogeography

  • Fossils confirm evolution patterns

    • Older deposits: simple organisms 

    • Recent deposits: complex, modern-like organisms 

  • Fossil distribution explained by plate tectonics and continental drift

    • Ex: fossils shared between Africa, India, and Antarctica


Summary of Contributions

  • Modern paleontology: unearthed key fossils (eg. feathered dinosaurs, human ancestors) 

  • Plate tectonics: explains fossil distribution and Earth’s surface features

  • Molecular genetics: strengthens evidence for shared ancestry and new adaptations