Evolution and Speciation Notes

A4.1 Evolution and Speciation

Evidence for Evolution

  • Predictive and Explanatory Power: The theory of evolution by natural selection possesses strong predictive and explanatory capabilities, making it unlikely to be disproven.
  • Pentadactyl Limb: The shared five-fingered (pentadactyl) hand structure in humans and the foot bones of the ancient reptile Captorhinus (280 million years old) suggest common ancestry.
    • This shared anatomy of limbs with diverse functions provides evidence for evolution.

Analogous and Homologous Structures

  • Analogous Structures: Similar in form and function but not due to common ancestry (e.g., bat wings and seagull wings).
    • Develop due to similar selection pressures.
  • Homologous Structures: Structures with similar anatomical position and structure despite differences in function, indicating common ancestry.
    • Organisms with a common ancestry subjected to different selection pressures become increasingly different.
    • Homologous structures provide evidence of evolution.
  • Human and Bonobo Ape Hands: Considered homologous structures.
  • Opposable Thumb: Significant for grasping and manipulation, with significance to evolution.

A4.1.1 Evolution as Change in Heritable Characteristics

  • Definition: Evolution is a change in the heritable characteristics of a population over time.
  • Heritable Characteristics: Traits inherited by offspring from parents.
  • Mechanism: Natural selection (Darwinism).
  • Acquired Characteristics: Changes during an organism's lifetime (e.g., a tree's asymmetric form due to wind).
    • Lamarckism: The earlier theory of inheritance of acquired characteristics, proposed by Jean-Baptiste Lamarck, has been falsified.
    • Acquired characteristics are not inherited and do not lead to evolution.

Theories: Pragmatic Truth

  • Pragmatic Theory of Truth: An assertion is considered true if it "works."
  • Scientific Knowledge Claims: Based on observations, forming generalizations, and testing them.
  • Scientific Theory: If generalizations are supported, a theory emerges that explains and predicts observations.
  • Evolution by Natural Selection as Pragmatic Truth: Explains antibiotic/pesticide resistance and homologous/analogous structures; regarded as a theory due to science's inability to prove it formally, despite extensive supporting evidence.

A4.1.2 Evidence from Base Sequences

  • Genetic Change: Evolution entails changes in the base sequences of DNA or RNA and amino acid sequences of proteins.
  • Coronavirus Evolution: Changes in the base sequence of the genes of the COVID-19 coronavirus affected viral traits, allowing new variants to spread.
  • Sequence Comparison: Closely related species have fewer differences in base sequences.
    • This is explained by species gradually diverging from a common ancestor due to natural selection.
  • Cladograms: Based on sequence differences, they match classifications based on morphology and lineage splits.
  • Hox Gene Family: Occurs widely in animal genomes and determines the body plan during development.
    • Similarities between Hox genes suggest common ancestry, duplication, and modification for different functions.
    • Found in cnidaria and bilateria (animals with a head-to-tail axis).

Data-Based Questions: Convergence and Divergence of Sequences

  • Sequence Divergence: After a clade splits, base and amino acid sequences diverge, with more time since the split resulting in more differences.
  • Ancestral Convergence: Looking back at ancestry, the closer to a common ancestor, the fewer sequence differences.
  • Monocots and Eudicots: Sequence convergence was tested using amino acid sequences of proteins in monocots and eudicots.
    • Observed sequence differences suggest evolution (1 \times 10^{-132} probability of not being due to evolution).

A4.1.3 Selective Breeding

  • Artificial Selection: Humans have selectively bred animals and plants for specific purposes (e.g., meat production in sheep, transport in horses, food in wheat).
  • Differences from Wild Species: Domesticated breeds and crops differ significantly from their wild counterparts.
  • Rapid Evolution: Artificial selection demonstrates the potential for rapid evolution.
  • THC Content in Cannabis: Artificial selection has quadrupled the average THC content in cannabis over 23 years.

A4.1.4 Homologous Structures

  • Unity of Type: Similar bone structures in the forelimbs of humans, moles, horses, porpoises, and bats.
  • Pentadactyl Limbs: Features with similar anatomical position and structure despite differences in function.
    • Bone Structure: Humerus, radius, ulna, carpals, metacarpals, and phalanges in forelimbs, and femur, tibia, fibula, tarsals, metatarsals, and phalanges in hindlimbs.
  • Vertebrate Classes: Amphibians, reptiles, birds, and mammals share the same bone pattern in their limbs.
  • Evolutionary Explanation: Homologous structures are inherited from a common ancestor but have evolved for different functions.
  • Vestigial Organs: Reduced structures with no function (e.g., teeth in baleen whale embryos, pelvis in whales, human appendix).
    • Easily explained by evolution as structures being gradually lost.

A4.1.5 Convergent Evolution

  • Analogous Structures: Similarities between structures with different origins performing similar functions (e.g., tails of fish and tail fins of whales).
    • Develop due to convergent evolution.
  • Cladistics: Used to deduce the evolutionary origins of organisms and their structures.
  • Central Nervous Systems (CNS):
    • In annelids, arthropods, and vertebrates, CNS development is associated with a similar pattern of homeobox gene expression.
    • However, nervous system development in other bilaterians is different, suggesting nerve cords evolved independently in annelids, arthropods, and vertebrates.
    • Therefore, CNS in these groups are analogous rather than homologous.
  • Eye Structure:
    • The human eye has nerve fibres in front of the retina and a blind spot, while the octopus eye has nerve fibres behind the retina and no blind spot.

A4.1.6 Speciation

  • Definition: The splitting of pre-existing species into new species.
  • Process: When two populations of a species become separated, natural selection acts differently on each, causing them to evolve in different ways.
    • If they no longer interbreed upon reunion, they have evolved into separate species.
  • Fractal Tree Analogy: Used to illustrate the process of splitting.
  • Explosive Species Diversification: In some groups, speciation has happened many times, leading to many species over a wide area (e.g., Zosterops or white-eyes).

A4.1.7 Reproductive Isolation and Differential Selection in Speciation

  • Speciation Requirements: Reproductive isolation and differential selection.
  • Gene Flow: Interbreeding causes mixing of genes, speciation depends on separation and divergence. Barriers preventing gene flow are needed.
  • Geographical Separation: Common cause of reproductive isolation, due to physical barriers like mountains, rivers, or oceans.
  • Differential Selection: Significant differences in selection pressures causing traits to diverge.
  • Lava Lizards of the Galápagos: Example of geographical isolation and speciation, with multiple species formed by migration to different islands and adaptation to distinct selection pressures.

Data-Based Questions: Flightless Steamer Ducks

  • Steamer Ducks: Four species of Tachyeres genus in southern Chile and Argentina.
  • Reproductive Isolation: Populations could have become reproductively isolated due to glaciation and sea level changes.

A4.1.8: Sympatric and Allopatric Speciation (AHL)

  • Allopatric Speciation: Occurs when populations in different geographical areas become separate species due to geographical separation.
  • Sympatric Speciation: Occurs when a population in the same geographical area splits into non-interbreeding populations.
  • Reproductive Isolation: In sympatric populations, due to behavioral (e.g., cichlid fish in Lake Massoko) or temporal differences (e.g., winter pine processionary moth).

A4.1.9: Adaptive Radiation (AHL)

  • Adaptations: Characteristics that make an individual suited to its environment.
  • Founders: Individuals migrating to a new area.
  • Ecological Niche: Availability of an ecological niche not fully exploited by other species causes rapid adaptation.
  • Adaptive Radiation: Pattern of diversification where species evolve from a common ancestor to occupy a range of ecological roles, minimizing competition and promoting coexistence.
  • Darwin's Finches: Example of adaptive radiation on the Galápagos Islands, with beak adaptations for different food sources.
  • Brocchinias: Genus of bromeliads on the Guiana Shield showing adaptive radiation with nutrient-capture strategies.

A4.1.10: Barriers to Hybridization (AHL)

  • Interspecific Hybrids: Produced by cross-breeding different species, often sterile due to genetic incompatibilities.
  • Hybrid Sterility: Prevents mixing of alleles between parent species.
  • Courtship Behavior: Prevents interspecific hybridization by ensuring mating within the same species, explaining diversity especially among birds.
  • Hybrid Swarms: Occur when closely related species overlap and produce fertile hybrids, reversing speciation and causing loss of biodiversity (e.g., Hawaiian ducks).
  • Honey Bees: Interspecific hybridization is prevented in honeybees due to release of pheromones and subsequent mating flights.

A4.1.11: Abrupt Speciation in Plants (AHL)

  • Polyploidy: Organism with more than two sets of homologous chromosomes.
  • Autotetraploidy: Four sets of chromosomes from the same organism, often with low fertility.
  • Allotetraploidy: Result of interspecific hybridization followed by chromosome duplication, overcoming fertility issues and creating new species.
  • Horse Chestnut Trees: Example of hybridization and allopolyploidy leading to new species.

A4.2 Conservation of Biodiversity

  • Factors Causing Extinction: Habitat loss, pollution, overexploitation, invasive species, climate change.

A4.2.1: Biodiversity Definition

  • Biodiversity: Abbreviation for "biological diversity", defined as the variety of life, existing at multiple levels:
    • Ecosystem diversity
    • Species diversity
    • Genetic diversity within species

A4.2.2: Current vs. Past Biodiversity

  • Current Estimates: Fewer than two million species named, with estimates ranging between 2 and 10 million eukaryotic species; prokaryote estimates are less reliable.
  • Past Levels: Deduced from fossil evidence showing variations, with five mass extinctions in history.
  • Sixth Mass Extinction: Predicted to be caused by human activity, threatening biodiversity levels.

A4.2.3: Anthropogenic Species Extinction

  • Extinction Causes: Overharvesting, habitat destruction, invasive species, pollution, global climate change.
  • Giant Moas, Atitlan Grebes, Mount Glorious Torrent Frog: Extinction examples are discussed.

A4.2.4: Causes of Ecosystem Loss

  • Direct and Indirect Causes: Land-use change for agriculture, urbanization, overexploitation, mining, dams, water diversion, fertilizer leaching, climate change.
  • Mixed Dipterocarp Forest of Southeast Asia and Aral Sea: Ecosystem loss examples.

A4.2.5: Evidence for a Biodiversity Crisis

  • IPBES: Evidence gathered by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services.
  • Monitoring: Collecting variables include population size, species range, ecosystem diversity, species richness, and fragmentation of ecosystems.
  • Citizen Science: Data collected by individuals over long periods can help detect harmful changes.

Applying techniques: Use of Simpson's diversity index

  • D = \frac{N(N-1)}{(\sum n(n-1)}
    Where: D=diversity index, N = total number of organisms of all species found, n = number of individuals of a particular species

Calculates the diversity by dividing the number of species by their total size.

Other information

  • Audubon Society: This society hosts an annual bird count, and can answer questions based on its collected data such as:
    • Has the average latitude where a particular species is observed shifted northward due to climate change over the past 40 years?
    • How has the presence in the Great Lakes Region of the invasive and destructive emerald ash borer beetle (Agrilus planipennis) impacted the population of birds that feed on ash seeds / birds that feed on beetles / birds that nest in dead trees?