EVOLBIOLEC: Evidences of Evolution

• Observations of Biological Evolution

  1. Fossil record
  2. Biogeography
  3. Convergent Evolution
  4. Embryology
  5. Selective Breeding
  6. Homologies/Analogies
• Fossil Records

  • Preserved remains of once-living organism
  • Most direct evidence of evolution
  • >10,000 years old to be considered as a fossil
• Paleontology is the science focused on studying fossils (age, formation, evolutionary significance)
• Successive evolutionary change is observed when old fossils are compared with younger fossils. The layer of sedimentary rocks provide information on geologic events

  ~ 300,000 fossil species discovered so far (<1% of all species which ever existed are represented in the fossil record [Prothero, 2007]
• Fossils are rare due to biological factors and geological factors.

  Biological factors are

  • structure of the organism
  • population of the species
  • length of time the species existed

  Geological factors are

  • habitat
  • geographical location
  • type of rock
• Example of fossils are Tyrannosaurus rex which existed for over 2 million years (compared to the 250,000 years humans have existed). An estimated 2.5 billion T. rex existed during this time. Complete fossil of T. rex that exist ~32 fossils.
• Fossilization processes include:

  • permineralization,
  • adpressions and carbon films,
  • cast and molds
  • bioimmuration
• Permineralization - Organic materials in bones and wood are replaced by minerals
• Adpressions and carbon films

  - Forms when plant/animal is buried in sediment and the carbon leaves imprints on the substrate
• Cast and Molds

  • Specimen is covered with sediment, when the organic material decomposed, a mold is formed
  • When minerals seeps into the mold, a cast is formed
• Bioimmuration

  • When an encrusting organisms (such as bryozoan, corals) grows over other sessile organism which may leave an impression of the covered organism
• Types of fossils

  • original remains (true form fossils)
  • index fossils
  • trace fossils
• Original Remains (True form fossils)

  • More or less complete organism preserved in amber, tar or ice
• Index Fossils

  • fossils used to identify or define a geological period. Usually based on fauna.
• Trace fossils

  • Preserved traces of activities (footprints, nest, burrows, coprolites)
  • Reflects animal behavior, locomotion, and diet
• Transitional Fossils

  • Fossilized remains of organisms which shows both the traits of an ancestral group and descendant group.
  • Transitional fossil ≠ Missing Link
  • Transitional fossil ≠ Direct ancestor
• The Idea of a missing link

  • Missing link = unscientific term for “transitional forms”
  • Based on two ideas

  1. The Great Chain of Being
  2. Orthogenesis

  • Implies that evolution is linear and progressive
• The Great Chain of Being – from lower forms into higher forms
• Orthogenesis – the simpler the structure, the more primitive it is
• Examples of Transitional Forms:

  • Triadobatrachus, transitional form between elongated amphibians and anurans
  • Ambulocetus natans, transitional form between terrestrial and aquatic mammals (cetaceans)
  • Tiktaalik roseae, transitional form between fish and tetrapods
  • Evolution of horses
  • Rhynia, transitional form between mosses and early vascular plants
  • Runcaria, a precursor to seed plants
• Is it possible to clone an extinct animal from a fossil?

  • Depends on several factors:
  • Type of fossil
  • Age of the fossil
  • DNA’s half-life is around 521 years.
  • Impossible to clone non-avian dinosaurs (unless we reverse engineer their living relatives – the avian dinosaurs).
  • Available technology
• Biogeography

  • Study of the geographical distribution of extinct and modern species.
  • Geography plays a role in evolution of species.
  • Isolated continents and island groups have evolved their own unique plant and animal communities
• • Species in islands originated from the mainland.
  • Species in islands are generally smaller compared to their mainland ancestors (island / insular dwarfing).
  • Movement of land masses also plays an important role in evolution.
• Island gigantism is a biological phenomenon in which animals living on an island grow much larger in size than their mainland relatives in the absence of predators.
• Iterative Evolution

  • Re-evolution of traits or body plans from the same ancestral lineage at different points in time.
  • Re-emergence of traits as a product of similar selective pressures
• Homologies

  • Fundamental similarity that occurs due to descent from a common ancestor
  • two or more species may have similar traits that was originally found in the common ancestor.
• Homologies can be anatomical, developmental, or molecular.
• Convergent Evolution

  • Species from different lineages sometimes become anatomically similar due to similarity in environmental conditions they occupy
  • Natural selection promotes adaptation to environment
  • Results in the development of analogous structure
• In animals…

  • Similarity in body plans – e.g. dolphins and ichthyosaurs, pterosaurs and bats, snakes, caecilians, glass lizards
  • Echolocation
  • Carcinization – turning into a crab-like form (king crabs, porcelain crabs, hermit crabs)
  • Anguilliformity – turning into an eel-like form
  • Camera eye – cephalopod and human eyes
  • Flight and flight patterns – birds and bats, flying squirrels and flying lemurs
  • Insect mouthparts – sucking mouthparts of fleas and mosquitoes
  • Opposable thumbs – apes, humans, and pandas
• Similarities in body plans. Top row: Ichthyosaurs (a marine reptile) and dolphin (a marine mammal) independently developed a body plan suited for fast swimming. Bottom row: many group of lizards evolved into limbless forms from legged ancestors.
• In plants…

  • Carbon fixation
  • Adaptation to heat and dessication (e.g. Cactaceae and Euphorbiaceae)
  • Storage of food
  • Fruits and seed dispersal
  • Myrmechocory – seed dispersal by ants evolved more than a 100 times independently
  • Carnivory
• Barnacles – the animal that made Darwin mad – previously classified as mollusks due to the appearance of the adult but was later reclassified as a crustacean based on the similarity with the larva of other crustaceans.
• Selective Breeding

  • Programs and procedures designed to modify traits in domesticated species through artificial selection
  • Made possible by genetic variation
• Pathways to Domestication

  1. Commensal Pathway - partnership (wolves to dogs)
  2. Prey Pathway - game to herd management (ruminants)
  3. Directed Pathway - human control (horses)