Chapter 22-An introduction to evolutin

Chapter 22: An Introduction to Evolution

Key Concepts

• Overview of Evolution

• Evidence of Evolutionary Change

• Molecular Processes Underlying Evolution

The Theory of Evolution

• Evolution: Heritable change in characteristics of a population from one generation to the next.

  • Microevolution: Changes within a single gene in a population over time.

  • Macroevolution: Formation of new species or groups of species.

Microevolution or Macroevolution

• Microevolution Examples:

  • Mosquitoes evolving resistance to DDT

  • Bacteria developing resistance to antibiotics

  • New COVID strains

• Macroevolution Examples:

  • 1,600 species of African cichlid fishes in the African Great Lakes

  • Development of 4-legged organisms from lobes

Definitions of Terms

• Species: Group of related organisms that share a distinctive form and can interbreed to produce viable offspring.

• Population: Members of the same species that are likely to encounter and interbreed with each other.

History of the Theory of Evolution

• John Ray (Mid to Late 1600s): First describer of species and classification system.

• Carolus Linnaeus: Expanded on Ray’s ideas; developed taxonomy and recognized speciation.

Late 1700s Developments

• George Buffon: Proposed that life has a history and suggested life originated from unorganized matter, evolving as species migrated to new habitats.

  • Explained the discovery of fossil elephants in Siberia and North America by citing migration and environmental changes.

Jean-Baptiste Lamarck** (Late 1700s)

• Proposed organisms evolve towards perfection through inheritance of acquired characteristics.

  • Giraffes' long necks due to behavior (reaching for tall trees) and predicted traits could disappear without the behavior.

Thomas Malthus

• An economist who stated:

  • Only a fraction of a population survives and reproduces due to competition for resources.

  • Population growth outpaces food supply, leading to struggle for existence.

Charles Darwin** (Born 1809)

• British naturalist who evolved the theory of evolution through observations during his voyage on the Beagle from 1831 to 1836.

  • Noticed species variations, like finches on the Galapagos Islands, leading to his ideas on natural selection.

Darwin’s Finches

• Different species adapted their beak shapes to exploit available food sources:

  • Ground Finches: Crushing mode.

  • Tree Finches: Grasping mode.

  • Warbler Finches: Probing mode.

Descent with Modification

• Evolution based on variation within species (traits are heritable).

• Natural selection occurs as more offspring are produced than can survive, with individuals possessing favorable traits competing better for limited resources.

Peter and Rosemary Grant – Drought Study

• Conducted a study over years in Daphne Major, examining the relationship between beak size and seed size.

  • Larger beaks resulted from survival advantages during drought conditions which favored larger seeds.

Factors Affecting Beak Size

• Hypothesis: Environmental conditions like drought affect seed size, influencing beak size in finches.

  • Experiment involves measuring beak depths before and after drought conditions.

Methodology Summary

1. Measure beak depth of adult finches in 1976.

2. Re-measure offspring after drought conditions in 1978.

Understanding Results

• Graph analysis indicating beak depth and number of birds.

  • X-axis: Beak Depth; Y-axis: Number of birds.

  • Changes in beak size observed before and after droughts.

Selective Breeding (Artificial Selection)

• Used to modify desirable traits in domesticated species; nature versus breeders in choosing parental traits.

• Examples include dog breeds and selectively bred plants.

Evidence of Evolutionary Change

• Types of evidence supporting evolution:

  • Fossil record

  • Biogeography

  • Convergent evolution

  • Selective breeding

  • Homologies: anatomical, developmental, molecular.

Biogeography

• Study of geographical distribution of species; isolated groups evolve distinct communities.

  • Example: Darwin’s finches and island foxes evolving from mainland species.

Fossil Record

• Layers of sediment reveal evolutionary history; newer sediments are on top.

  • Example: Tiktaalik as a transitional fossil linking fish and tetrapods.

Homologies

• Similar traits due to common ancestry, appearing in anatomical, developmental, or molecular formats.

• Vestigial Structures: Anatomical remnants with no function, e.g., bony tail in human embryos.

Developmental and Molecular Homology

• Embryonic similarities indicate common ancestry; Molecular Homology: DNA similarities among species denote a shared lineage.

Molecular Processes Underlying Evolution

• Homologous Genes: Genes from a common ancestor showing divergence in different species affecting their functions.

  • Paralogs: Homologous genes within a single species due to gene duplication.

Horizontal Gene Transfer**

• Transfer of genetic material between organisms not related through descent; critical in bacterial evolution.

• Mechanisms include conjugation, transformation, and transduction.

Evolution at the Genomic Level

• Chromosomal changes comparing species like humans and apes, exemplifying evolutionary divergence.

Evolution Evidence Summary**

• Collectively supports concepts of evolution, emphasizing the interconnectedness of life forms through historical and genetic frameworks.