Evolution and Biodiversity

EVOLUTION

Overview of Biodiversity

  • **Main Topics Under Biodiversity: **

    • Evolution

    • Natural Selection

    • Classification

    • Extinction

    • Speciation (AHL)

    • Gene Pools (AHL)

    • Cladistics (AHL)

EVOLUTION

Key Concepts

A4.1.1: Evolution as Change in Heritable Characteristics

  • Definition: Evolution is defined as the cumulative change in the heritable characteristics of a population.

    • Characteristics change gradually and accumulate over extended periods.

    • Genetic factors drive these changes, transferred between generations in the form of alleles.

    • Evolution occurs at the population level rather than at the individual level.

  • Theoretical Status of Evolution: While backed by substantial evidence, evolution remains classified as a theory.

A4.1.2: Evidence for Evolution

  • Evidence for evolution includes:

    • Comparison of genomes or gene sequences

    • Fossil record analysis

    • Artificial selection (selective breeding) evidence from domesticated species

    • Comparative anatomy revealing homologous structures

A4.1.3: Evidence from Selective Breeding

  • Selective Breeding: This form of artificial selection, where humans decide which individuals to breed, demonstrates that heritable traits can change over time, leading to rapid evolution.

A4.1.4: Homologous Structures

  • Homologous Structures: These structures suggest evolutionary relationships due to their similarity of anatomy and different functions arising from a common ancestor (e.g., human forearm, whale flipper).

A4.1.5: Convergent Evolution

  • Convergent Evolution: Refers to the development of analogous structures (similar functions, different ancestry) in unrelated lineages due to similar environmental pressures (e.g., wings of bats and wings of insects).

A4.1.6: Speciation

  • Speciation: The process by which new species evolve from pre-existing species, often from divergent evolutionary changes.

  • Significance of reproductive isolation and differential selection: Helps accumulate differences between two populations leading to speciation.

A4.1.7: Mechanisms of Speciation

  • Explains reproductive isolation - factors include:

    • Geographical isolation

    • Mechanical isolation

    • Temporal isolation

    • Behavioral isolation

EVIDENCE FOR EVOLUTION

Fossil Record

A4.1.1

  • Definition: Fossils represent preserved remains or traces of organisms from the past.

    • Direct Evidence: From bones, teeth, shells, and leaves.

    • Indirect Evidence: From footprints, bite marks, and burrows.

  • The fossil record encompasses all known fossils, indicating gaps due to:

    • Rarity of fossilization

    • Preservation limitations (only hard parts of organisms preserve well)

    • Damage from predation, erosion, or human activities.

Relative Dating

  • Fossils dated based on the surrounding rock layers.

    • Fossils embed in sediment as layers of sedimentary rock form.

Absolute Dating

  • Involves dating fossils through radioactive decay of elements, like Carbon-14 to Nitrogen-14.

    • Carbon-14's half-life: Approximately 5730 years, useful for dating up to 62,000 years.

Insights from the Fossil Record

A4.1

  • Insights include:

    • Prokaryotes preceded eukaryotes

    • Ferns appeared before flowering plants

    • Invertebrates appeared before vertebrates

Comparative Anatomy

  • Used to infer evolutionary relationships through:

    • Homologous structures: Similar in anatomy but different functions, suggesting a shared ancestry.

    • Analogous structures: Similar function and appearance, but not through a common ancestor.

Examples

  • Homologous Structures:

    • Shared pentadactyl limb among vertebrates, vestigial organs like the human appendix.

  • Analogous Structures:

    • Wings of birds vs. insects, tails in diverse aquatic animals (e.g., fish and whales).

Convergent Evolution

  • Streamlined shapes in sharks and dolphins exemplify convergent evolution due to adaptation to similar environments, despite different evolutionary histories.

Molecular Evidence for Evolution

A4.1.2

  • Modern bioinformatics compare DNA or RNA sequences across multiple organisms to determine the evolutionary relationships.

  • The discrepancies in base and amino acid sequences among clades reveal divergence post-split from a common ancestor.

Speciation

A4.1.6 / A4.1.7

  • Speciation is driven by:

    • Accumulation of differences in two related populations leading to new species.

    • Reproductive isolation: These populations evolve separately due to various isolation types.

Example: Galapagos Finches

  • Illustrates speciation through geographical isolation and differential selection in response to environmental challenges.

Extinction

A4.1.6

  • Extinction diminishes biodiversity on Earth:

    • Approximately 99.99% of species that ever existed are now extinct.

  • Causes include:

    • Lack of necessary adaptations in the surviving individuals, leading to inability to adapt to changing environments.

Major Extinct Species Examples

  • Woolly mammoths, dodos, Tyrannosaurus rex.

    • Contemporary discussions consider the potential of de-extinction through advanced DNA recovery techniques.

Anthropogenic Effects and Conservation Efforts

A4.2.3 / A4.2.4

  • Biodiversity Definitions:

    • Ecosystem diversity reflects the quantifiable variety of ecosystems.

    • Species diversity measures through species richness and evenness.

While these notes are extensive, they cover only some sections of the provided transcript. Continuing these notes would delve into deeper details regarding classification, conservation strategies, the implications of extinction on biodiversity, and methods to measure these complexities, including practical questions and answers relevant to academic assessments.