17.3 Darwin Presents His Case- Student..

Darwin's Contribution to Evolution

• Charles Darwin formulated the theory of natural selection after years of observation and study.

• Although he had a draft ready for publication for about 20 years, he sought additional evidence before making his ideas public.

• In 1858, he published "On the Origin of Species," explaining his theory in detail and providing supporting data.

• His work describes a scientific mechanism for evolution similar to artificial selection.

Components of Natural Selection

Key Conditions

• Struggle for Existence: Organisms compete for limited resources.

• Variation and Adaptation: Individuals show variation in traits, some of which may enhance survival.

• Fitness: The ability to survive and reproduce based on advantageous adaptations.

Adaptations

• Adaptations enhance survival and reproduction and can take various forms:

  Adaptations

  Adaptations enhance survival and reproduction and can take various forms:

  • Morphological: Features that affect the structure of an organism, enabling it to adapt to its environment.

    • Example: Features like a tiger’s claws.

  • Coloration: The use of colors and patterns for survival strategies, including camouflage to blend into the environment or mimicry to imitate other species.

    • Example: Camouflage or mimicry.

  • Physiological: Internal functions and processes that enhance an organism's ability to survive in its environment.

    • Example: Functions like photosynthesis in plants.

  • Behavioral: Actions taken by organisms to survive and reproduce, often through learned or instinctual behavior.

    • Example: Actions such as evading predators.

• Examples:

  • Predatory species that are faster catch more prey.

  • Prey species that are better camouflaged avoid being caught.

Understanding Fitness

• Fitness is defined by how well individuals can survive and reproduce.

• Variations in adaptations influence an organism's fitness:

  • High fitness: Well-adapted traits lead to higher reproductive success.

  • Low fitness: Poorly adapted individuals may not survive to reproduce.

• Evolutionary terms emphasize that survival also means reproducing and transmitting adaptations.

Natural Selection in Action

• Example of Grasshoppers:

  • Green grasshoppers are better camouflaged than yellow grasshoppers, resulting in higher survival rates for green individuals in their environment.

Research on Bird Adaptations

• Explore how various birds have adapted their beaks, feet, and feathers to fit their environments.

The Process of Natural Selection

• The process requires:

  • More individuals born than can survive, creating a struggle for existence.

  • Heritable variations that affect survival and reproduction.

  • Variations in fitness leading to differential reproductive success.

Evolution and Common Descent

• Charles Darwin's theory suggests that species evolve from common ancestors with variations over time.

• Evidence of this process includes the fossil record showing changes in species.

• Through adaptations to limited resources, a single species can diverge into multiple new species.

Evolutionary Tree Thinking

• All organisms are interconnected through a common ancestry.

• An evolutionary tree illustrates relationships among species:

  • Example: Tigers, lions, and cheetahs share a common ancestor.

  • Further back, connections exist between mammals and other groups like birds and reptiles.

  • The concept of common descent showcases life's unity and diversity.

Assessment Questions

1. Identify the three conditions necessary for natural selection.

2. Discuss how evolutionary theory accounts for the unity and diversity of available life.

3. Construct arguments on why an organism's fitness is dependent on its environment.

Answer Key Highlights

1. The conditions are survival, reproduction, and the passing of adaptations to the next generation.

2. Unity in living things comes from descent from common ancestors, while diversity arises due to adaptations to distinct environments.

3. An organism's fitness is linked to environmental demands, illustrated by adaptations like camouflage in arctic foxes.

Lesson 17.4 – Evidence of Evolution

Evidence for Evolution

Methods to Determine Evolutionary Relationships:

• Biogeography

• Fossil Record

• Anatomical Evidence

• Embryological Evidence

• Genetics and Molecular Evidence

Biogeography

• Biogeography studies the distribution of life across time and space. Darwin's observations led him to conclude that Galápagos species evolved from mainland species due to natural selection. Similar species in different regions indicate distantly related origins adapting to similar environments.

The Age of Earth and Fossils

• Earth's age, approximately 4.5 billion years, established through radioactive dating supports extensive evolutionary time. Fossil discoveries illustrate the gradual evolution of species from extinct ancestors, such as whales from land-dwelling relatives.

Comparing Anatomy and Development

Homologous Structures

• Similar anatomy with different functions indicates common ancestry (e.g., a bird’s wing and a human’s arm).

Analogous Structures

• Similar functions with different anatomy suggest no recent common ancestor (e.g., bee and bird wings).

Vestigial Structures

• Inherited but non-functional structures (e.g., dolphin hipbones) give insight into evolutionary history.

Embryology and Development

• Similar early developmental stages in vertebrates imply common ancestry.

Genetics and Molecular Biology

• The shared genetic code among organisms provides strong evidence of common descent, supported by homologous genes and proteins.

Testing Natural Selection

• The Grants’ research on Galápagos finches emphasizes the importance of heritable variation for adapting to environmental changes, demonstrated by beak size changes in response to drought conditions.