Week 4 WSP: Evolution - Transitions and Innovations

Week 4 WSP: Evolution - Transitions and Innovations

1. Major transitions in Evolution

   • Entities capable of independent replication before transition can only replicate as a part of a larger unit of transition
   • Associated with division of labour and task specialisation
   • Change in way information is transmitted between generations

2. Big 8 transitions

   • Replicating molecules - populations of molecules in compartments
   • Independent replicators (RNA) - chromosomes
   • RNA as genes and enzymes - DNA as genes; proteins as enzymes
   • Prokaryote - eukaryotes (nucleus in cell)
   • Asexual clones - sexual populations
   • Protists - multicellular organisms
   • Solitary individuals - colonies with non-reproductive castes
   • Primate societies - human societies with language

3. Increasing Complexity

   • Increasing complexity, information storage, transmission and interpretation
   • Humans - several leaps of complexity: evocative of ladder of progress to humans

4. Bilateral Symmetry

   • One longitudinal axis of symmetry
   • Anterior and posterior ends; dorsal and ventral sides
   • Higher mobility
     • Direction of movement better defined
     • Resistance to water or sediments reduced
     • More efficient seeking food + mates, avoiding predators
   • Greater differentiation/compartmentalisation of body parts
   • Cephalization
     • Centralisation/increased complexity of nervous system
     • Quick, precise responses to stimulation
   • Assisted complexity in nervous system

5. Nervous System

   • Changed way information transmitted between cells
   • Altered nature of individuals - heredity based on transmission of acquired information
   • Major transition as change in way information is stored, transmitted and processed
   • Transmission between individuals; neural transmission occurs between cells within an individual
   • Specificity and speed - integration and memory storage

6. Coelom

   • Fluid filled body cavity formed within mesoderm - central germ or tissue layer
   • Cushions internal organs; acts as hydrostatic skeleton
   • More space for complex organs to develop
   • Highly efficient circulatory, excretory, digestive and reproductive system
   • Facilitated subsequent evolution of
     • Segmentation
     • Rigid internal skeletons
     • Diverse methods of locomotion
     • Larger body sizes

7. Plant Generation switch

   • Two alternating generations
   • Haploid (1n = 1 set of chromosomes), diploid = 2 sets
     • Gametophyte produces sperm + eggs
   • Gametes unit to form diploid (2n) zygote - SPOROPHYTE
   • Sporophyte produces 1n spores - GAMETOPHYTE
   • Vascular plants evolved sporophyte-dominated life cycles
     • Two sets of genes help avoid expression of deleterious traits prompted by mutations caused by high UV
     • Allowed major increase in plant diversity and complexity but may be due to evolution of vascular tissue

8. Evolutionary Innovations

   • Transition: major increases in organisational complexity and information transmission
   • Innovation: any new evolutionary trait in broad sense

9. Life Originate

   • Phylogenetic evidence (biological comparisons)
     • Examine tree of life to determine whether earliest branching groups are aquatic or terrestrial
   • Palaeontological Evidence (fossils + geology)
     • Examine fossil record to determine whether earliest-appearing groups are aquatic or terrestrial

10. Phylogenetic Evidence

    • Watery Animal Origins
      • 24 of 35 phyla exclusively marine; includes all early branching groups
      • 10 phyla are marine, freshwater and terrestrial
      • Strongly suggests animal life evolved in oceans
    • Watery Plant Origins
      • Plants evolved from Green Algae which are wholly aquatic
      • Share chlorophylls a/b similar chloroplast structure, cellulose in cell walls, starch as storage material

11. Earliest Record of life

    • Evolved 3.5 Gyr ago
    • Evidence 3.4-3.3 Gyr old Stromatolities and biofilms
    • Diversity stromatolie form suggests diverse microbial communities
    • Mostly photoautotrophic cyanobacteria
    • All marine

12. Phun with Sulphur

    • Pyrite crystals associated with fossil cell suggestive of sulphur-metabolising bacteria
    • Some cells organised into chains or tubular sheaths; other show folded cell walls and occur in clusters
    • Associated carbonaceous material has carbon and nitrogen isotropic compositions consistent with biological nutrient cycling

13. Oxygen

    • Little or no free atmospheric oxygen up to 2.5 Gyr ago
      • Cyanobacteria producing O2 via photosynthesis
    • Plants supplied much more atmospheric O2

14. Ode to O2

    • Facilitated Evolution of Multicellular Organisms
      • Highly efficient recovery of energy contained in chemical bonds with glucose --> oxidative phosphorylation
      • Produces large amounts of ATP providing energy for developing and maintaining complex organisms
      • EDIACARAN PERIOD: 580 MYR AGO ALL AQUATIC
      • CAMBRIAN PERIOD: 530 MYR AGO ALL AQUATIC
    • Development of Ozone Layer
      • Protects against lethal levels of UV radiation
      • Removed a major barrier to shift of life onto land

15. Confronting Continent

    • Life and each kingdom of living organisms evolved in oceans
    • Oceans cover 70% of Earth
    • Land would have been a very harsh environment 650 - 450 Myra ago
    • Challenges include
      • Avoiding desiccation
      • Maintaining structural integrity
      • Effective reproduction
      • Effective dispersal and locomotion
      • UV radiation