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Lecture 3 - The Scientific Method and Evolutionary Theory

  • Is biological anthropology a science? What is science?

    • Science: a set of methods for deriving knowledge about the world; an empirical process

  • Scientific Method (steps):

    • 1. Observation

    • 2. Hypothesis

    • 3. Experiment

    • 4. Conclusion (hypothesis supported or rejected)

    • 5. Publish

  • Theory: a hypothesis that has been tested repeatedly without being rejected (e.g., evolution)

  • What is Evolution?

    • A change in the frequency of alleles in a population over time

    • A theory used to describe biological change

    • Supported by multiple lines of evidence

  • Charles Darwin

    • On the Origin of Species (1859)

    • Described mechanics of evolutionary processes

  • Brief history of evolutionary thought (outline of major ideas and figures)

    • Ancient Greece: Plato and Aristotle

    • Essentialism: Life is changeless and consists of a limited number of fixed forms (essences)

    • Great Chain of Being (Aristotle): hierarchical arrangement with humans at the top

    • 16th century Christian Church: official position of fixity of species; species created by God; no change; Earth has a short history

    • Archbishop Ussher (1581–1656): Earth created in 4004 B.C. (popular medieval/early modern calendar dating)

    • Carolus Linnaeus: Systema Naturae (1735); binomial nomenclature (e.g., Homo sapiens); included humans in the primate order

  • Scientific & Industrial Revolutions and the breakdown of fixed-species ideas

    • Emergence of geological and biological evidence that challenged fixity

    • Example fossil: Darwinius masillae, an Eocene primate (~47 million years ago) found in Germany

  • Key historical figures and ideas (1700s–early 1800s)

    • James Hutton (1726–1797): Uniformitarianism – the forces shaping the Earth in the past continue to shape it today; Earth’s features result from long-term processes

    • Charles Lyell (1797–1875): Principles of Geology (1830) – provided evidence for uniformitarianism; calculations to estimate time for geological strata to accumulate; implied great Earth antiquity

    • Georges Cuvier (1769–1832): expert in comparative anatomy and paleontology; observed that geological strata contained unique assemblages; explanation for extinctions = catastrophism (catastrophes wipe out forms and are followed by replacement)

    • Jean-Baptiste Lamarck (1744–1829): first to hypothesize mechanisms of change; organisms adapt to environmental demands

  • Lamarckian evolution (mechanism)

    • Features develop or are modified according to the needs of the organism

    • The acquired characteristics are inherited

  • Thomas Malthus (1766–1834)

    • An Essay on the Principle of Population (1798)

    • In nature, overpopulation is checked by the availability of resources

    • Resources are not limitless; not all organisms can obtain adequate food; only some survive to perpetuate the species

  • Darwin and the voyage of discovery

    • HMS Beagle (1831–1836)

    • Galápagos finches: varied from island to island but similar to mainland relatives

    • Hypothesized that variation was adaptive

  • Natural Selection (Darwinian mechanism)

    • Conditions/steps:

    • 1. There is variation within species

    • 2. More individuals are born than survive; there is a struggle for existence

    • 3. Favorable adaptations are inherited (passed on to offspring)

    • 4. Successful variations accumulate, leading to the formation of new species over time

    • Darwinian fitness = reproductive success

  • Darwin’s fitness concept

    • Fitness is measured by reproductive success, not just survival

  • Shortcomings of Darwin’s theory (initial gaps)

    • Did not understand the source of variation

    • Did not understand the particulate nature of inheritance (genes)

    • Inheritance was understood as blending of parental traits

  • Mendel’s contribution to genetics

    • Gregor Mendel (1822–1884): established particulate inheritance; laid the foundation for genetics

    • His work reconciled Darwinian evolution with a mechanism for inheritance

  • Connections and implications

    • Evolution relies on variation, heredity, and differential reproductive success

    • The synthesis of geology, natural history, and genetics underpins modern evolutionary biology

    • Shifts in worldview from fixed species and creationist narratives toward dynamic, historical processes

  • Ethical, philosophical, and practical implications

    • Challenges to literal interpretations of fixed creation accounts

    • Supports scientific explanations for biodiversity and human origins

    • Informs fields from medicine and conservation to anthropology and ecology

  • Notation and definitions (quick reference)

    • Evolution: change in allele frequencies in a population over time

    • Allele frequency: probability of a given allele in the population’s gene pool

    • Fitness: reproductive success; contribution of an individual’s genes to the next generation

    • Uniformitarianism: present-day processes shaped Earth’s features; vast geological timescales

    • Catastrophism: abrupt, catastrophic events explain abrupt changes in life and ecosystems

    • Binomial nomenclature: two-name species designation (genus + species), e.g., ext{Homo sapiens}

    • Natural selection: mechanism by which evolution occurs via differential survival and reproduction

  • Key formulas and concepts (LaTeX)

    • Evolution as changes in allele frequencies: rac{dp_i}{dt}
      eq 0 ext{ for at least some alleles } i

    • Change in allele frequency between generations: riangle pi = pi^{(t+1)} - p_i^{(t)}
      eq 0 ext{ for some } i

    • Darwinian four-step outline (conceptual, not a numerical model): variation, overproduction, inheritance of favorable traits, differential reproduction

  • Summary takeaway

    • Early science established that life changes over time and that this change is driven by differential reproduction acting on heritable variation, with a robust intellectual lineage spanning geology, biology, and genetics

    • The scientific method provides a framework for testing these ideas, culminating in theories that synthesize evidence across disciplines