Darwin and Evolution

Lesson 2: Darwin and Evolution

History of Evolutionary Thought

  • Charles Darwin's Voyage:

    • In December 1831, Charles Darwin set sail on the HMS Beagle for exploration and observation of the natural world.

    • During this five-year journey, Darwin formed a hypothesis that species could change in response to their environment and habitat.

    • After his return, he documented these ideas in his seminal work: "On the Origin of Species by Means of Natural Selection".

    • Introduced the concept that evolution occurs through a process known as natural selection.

Influences on Darwin’s Ideas

  • Plato and Aristotle (Ancient Greece):

    • Proposed that every species has a perfect, “essential” form.

    • Variations among species were viewed as imperfections of this ideal form.

    • Noted that organisms could vary in complexity and could be organized accordingly.

  • Georges-Louis Leclerc (18th Century Naturalist):

    • Documented all known species of plants and animals.

    • Suggested that evolution or variation among species could result from environmental influences or the struggle for existence.

  • Carolus Linnaeus (Father of Modern Taxonomy):

    • Developed the binomial system of nomenclature (Genus species).

    • Believed that species have an ‘ideal’ form.

    • Introduced the concept of scala naturae: life is organized based on complexity, where less complex organisms occupy lower rungs and humans, angels, and gods reside at the top.

  • Erasmus Darwin (Grandfather of Charles Darwin):

    • Physician and naturalist, lightly hypothesized about evolution through observations of:

      • Animal development.

      • Human-driven animal breeding practices.

      • Presence of vestigial organs.

  • Baron Georges Cuvier:

    • Founded the science of paleontology.

    • Focused on dating fossils based on their location in geological strata.

    • Explained fossil changes through the theory of catastrophism: Catastrophic events lead to new species moving into an area.

  • Jean-Baptiste Lamarck:

    • Developed the first testable hypothesis of evolution.

    • Proposed that evolution results from the inheritance of acquired characteristics, emphasizing that the environment can induce phenotypic changes over time, which can be passed down to subsequent generations.

  • James Hutton:

    • Proposed a theory of slow, uniform geological change over time.

  • Charles Lyell:

    • Promoted uniformitarianism: the notion that natural processes observed today are consistent with those that have always taken place in Earth’s history.

  • Thomas Malthus:

    • Wrote "Essay on the Principle of Population", which argued that human population sizes are limited only by the availability of resources.

Darwin’s Theory of Evolution

  • Observations During Voyage:

    • Darwin observed both biological and geological aspects during his voyage on the HMS Beagle.

    • Key realizations included:

      • “The Earth is old.”

      • “Animals in one area can differ from those in another.”

    • This notion led to the field of biogeography, which studies the geographical distribution of organisms.

  • Age and Publication:

    • Darwin was 22 when he set sail in 1831, acting as the ship's naturalist (without pay).

    • His findings were not published until 1859.

Understanding Evolution

  • Definition of Evolution:

    • Evolution refers to the change in inheritable traits of a species across generations, commonly summarized as ‘CHANGE OVER TIME’.

  • Definition of a Species:

    • A species is defined as a group of organisms that can reproduce and produce offspring capable of reproduction.

    • Example: Phoenix dactylifera (Date Palm Tree).

Types of Evolution

  • Microevolution:

    • Describes small-scale changes within a single population.

  • Macroevolution:

    • Describes large-scale changes that affect species across populations.

Natural Selection as a Mechanism of Evolution

  • Publication of Findings:

    • In 1859, Darwin published "On the Origin of Species", in which he outlined the mechanism of evolution: NATURAL SELECTION.

    • Defined natural selection as the principle by which beneficial variations of traits are preserved while unhelpful traits are not; this process is sometimes referred to as **