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2: Evolutionary Theory

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    • Science

      • Use of empirical data to explain phenomena

    • Philosophy

      • Attempt to understand the nature of life and existence

    • The scientific method

      • Technique used in the construction and testing of scientific hypotheses

    • In order for something to be considered a scientific form of analysis, it must be:

      • Experimentally verifiable or falsifiable

      • Predictive

    • Hypothesis

      • Proposed explanation for a phenomenon; must be testable

    • Theory

      • A complex set of ideas that have undergone rigorous testing, analysis, assessment, and retesting; a well-supported general idea that explains a large set of factual patterns and predicts other patterns

    • Independent variable

      • Variable that is manipulated by the experimenter to produce an effect on the dependent variable

    • Dependent variable

      • Responds to the independent variable; measured by the experimenter

    • Control

      • Anything that is held constant and unchanged throughout an experiment

      • Any change in the control would indicate that there is an invalid relationship between the independent and dependent variable

    • Prior to 1800s:

      • View that Earth is young, fixed

      • Archbishop James Ussher: claimed earth is 6000 years old, based on biblical texts

    • Essentialism (Plato, 427-347 B.C.)

      • All organisms have essential characteristics that are unalterable

      • Species were fixed and unchanging (fixity of species)

    • Great Chain of Being (Aristotle, 384-322 B.C.)

      • Scale from simple to complex

      • Moving toward perfection

      • Divine intervention

    • Life ordered from simplest to most complex

      • Used to justify status in society

      • Sovereign rule given from God to the king…

      • Many were were told that their place in society was “biologically justified”

    • In summary:

      • Earth was young

      • Species were fixed and didn’t change

      • Organisms had an “ideal” form (any variation was seen as disformity)

      • “Simpler” organisms were ranked lower in the scale (Great Chain of Being) than more “complex” organisms

    Evolutionary Theory

    • The domestication of plants and animals had been occurring worldwide for a long time, so it's certainly possible that many probably had some questions and explanations for genetics and the concept of natural selection before Darwin...
    • Kitab al-Hayawan (Book of Animals) by Al Jahiz (776 - 868 A.D., Iraq)

      • Has been interpreted as an early discussion on the concept of natural selection.  

        • Animal mimicry – noted that certain parasites adapt to the color of their host

        • Discussed influence of climate, geographic region, and diet on living organisms

        • Discussed animal communication and intelligence

        • Discussed food chains, social organization of animals

    • Hippocrates (460-370 B.C.)

      • Beginning of the inheritance of acquired characteristics concept

        • Some traits (which are inherited) improve or hinder survival

        • Traits are inherited from parents

      • Greek physician – influential in medicine

      • “Hippocratic oath” – physician must swear, to a number of healing gods, to uphold specific ethical standards

    • Zhuangzi (369 BC – 286 B.C.)

      • The early philosopher Zhuangzi also discussed the idea of species changing over time (the idea that there are "building blocks" that lead to more complex life forms).

    • Carolus Linneaus (1707-1778)

      • Binomial nomenclature – taxonomic system for classifying organisms (Genus, species – example: Homo sapiens)

    Geologic Change on Earth

    • Stratigraphy

      • Nicholas Steno – Steno’s Law/Law of Superposition

      • Analysis of the order and position of stratigraphic layers

    • Catastrophism

      • Georges Cuvier (1769-1832)

      • Proposed that geologic epochs ended with large-scale, violent natural catastrophes, causing organisms to go extinct and be replaced by new organisms

        • Example: meteor strikes, massive floods, supervolcanoes, mega earthquakes

    • George-Louis Leclerc Comte de Buffon (1707-1788)

      • Critiqued catastrophism

      • Argued that catastrophic events are rare

      • Earth’s history can more likely be explained by uniform processes

    • James Hutton (1726-1797)

      • Deposition and erosion: self-regulating system on Earth

      • Earth must be much older than 6000 years

    • Uniformitarianism

      • Charles Lyell (1797 – 1875), James Hutton

      • Challenged catastrophism, as well

      • Changes on earth’s crust result from continuous, uniform processes over time (these processes occurred in the past and continue to occur in the present)

        • Examples: coastline reshaped by tsunami, destruction due to volcanic eruption, formation of mountain ranges, erosion

    • Charles Lyell

      • Charles Darwin was interested in Charles Lyell’s work with uniformitarianism

      • Influential to Darwin on his voyage on the Beagle

    • Erasmus Darwin (1731 - 1802)

      • Charles Darwin’s grandfather (also a scholar)

      • Believed that there is a “struggle for existence”

    • Thomas Malthus (1766 - 1834)

      • Human populations increase more rapidly than resources (competition)

      • Fitness – better “adapted” organisms are more reproductively successful

    • Jean Baptiste de Lamarck (to be discussed later)

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    2: Evolutionary Theory is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

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