Introduction to Evolution

Evolution – An Introduction

  • Worldview before Darwin
    • The scientific perspective prior to Darwin was dominated by ideas from Plato and Aristotle.
    • Plato believed in a realm of eternal and perfect forms, with the tangible world being an imperfect reflection.
    • Aristotle argued that organisms do not change and introduced the concept of the Scale of Nature (Scala Naturae).

The Scale of Nature (Scala Naturae)

  • Definition: A hierarchical classification of all beings, ranging from inanimate matter to humans and angels.
  • Origin: Attributed to Aristotle, this concept proposed a linear structure of life, supporting the belief in divine order.
  • Implications:
    • Encouraged investigation into the natural world as a reflection of divine organization.
    • Reinforced feudal hierarchical thinking, establishing social stratification.

Revolutionary Ideas in Evolution

  • Key Figures and Concepts:
    • Charles Darwin: Developed theories of evolution and natural selection.
    • Alfred Russel Wallace: Independently proposed theories of evolution via natural selection.
    • Gregor Mendel: Founded the study of inheritance; his work was later recognized for its importance in genetics.
    • Charles Lyell: Proposed uniformitarianism, suggesting that Earth’s features are the result of slow, gradual processes.
    • Georges Cuvier: Pioneered paleontology and inferred information about extinct species from fossil records.
    • Thomas Malthus: Examined human population dynamics and resource limitations, influencing Darwin's ideas on competition and survival.
    • Jean Baptiste Lamarck: Early theorist of evolution who proposed the ideas of use & disuse and inheritance of acquired characteristics, though now discredited.
    • James Hutton: Introduced gradualism, proposing that geological features develop slowly over time.

Key Historical Developments in Evolutionary Thought

  • Major Publications and Events:
    • 1795: Hutton proposes gradualism.
    • 1798: Malthus publishes "Essay on the Principle of Population."
    • 1809: Lamarck publishes his theory of evolution.
    • 1830: Lyell publishes Principles of Geology.
    • 1831-1836: Darwin's voyage on HMS Beagle, observing diverse species.
    • 1844: Darwin drafts his essay on the origin of species.
    • 1858: Wallace presents his theory to Darwin.
    • 1859: Publication of On the Origin of Species.
    • 1865: Mendel's work on inheritance.

Geological Evidence and the Age of the Earth

  • Study of Fossils:
    • Cuvier established paleontology through the study of fossils found in sedimentary rock layers, noting that deeper layers contained older fossils.
  • Key Concepts:
    • Geological processes observed today (e.g., erosion) were similar in the past.
    • The Earth is ancient, necessitating vast time scales to explain the stratification of rocks and fossils.

Lamarck’s Hypothesis on Evolution

  • Explanation for Giraffe's Neck:
    • Proposed that neck length evolved due to need (use and disuse) and that such traits were inheritable.
    • This concept of inheritance of acquired characteristics has been disproven.

Darwin’s Observations and Contributions

  • Voyage of the Beagle:
    • Key observations made in the Galápagos Islands significantly influenced Darwin’s theory.
    • Noted variation among species, notably Darwin’s finches, which adapted different beaks based on food sources.
  • Natural Selection:
    • Variations exist within populations.
    • Overproduction of offspring puts pressure on resources, leading to competition.
    • Those best suited to their environments survive and reproduce more effectively, a concept summarized as "survival of the fittest."
  • Tree of Life:
    • Darwin conceptualized the history of life as a branching tree rather than a linear progression (as proposed by the Scale of Nature).