Biological Principles and the Science of Zoology

Biological Principles and the Science of Zoology

Definition of Zoology

  • Zoology: Scientific study of animal life (Reference: Hickman et al. 2017).
    • Etymology:
    • Zoo: means animal.
    • Logy: means to study.
  • Guided by various essential principles:
    • The Scientific method
    • Guiding theories:
    • Natural selection
    • Mendelian Inheritance

What Is Life?

  • A complex question with deeper implications.
  • The properties of living systems today differ from those at the emergence of life.
  • Criteria for defining life may be more useful than concise definitions.
  • Eight (8) criteria proposed: living entities satisfy all; non-living do not.

Properties of Living Systems

  1. Chemical Uniqueness

    • Living systems demonstrate unique and complex molecular organization.
    • Utilize the same atoms and chemical bonds as non-living systems but arranged in complex molecules termed macromolecules which include:
      • Nucleic acids
      • Proteins
      • Carbohydrates
      • Lipids

  2. Complexity and Hierarchical Organization

    • Living systems exhibit a unique and intricate hierarchical organization.
    • Levels of complexity:
      • Macromolecules make up Cells
      • Cells form up to create Organisms
      • Organisms aggregate into Populations
      • Populations consist of Species
    • Emergence of new properties at successive levels of organization.

  3. Reproduction

    • Living systems are capable of self-reproduction at every level of biological organization:
      • Genes replicate (copying)
      • Cells undergo division
      • Organisms reproduce
    • Balance between heredity (faithful transmission of traits) and variation (unfaithful trait transmission) is critical, as extremes can be detrimental.

  4. Possession of a Genetic Program

    • A genetic program ensures faithful inheritance of traits.
    • Nucleic acids (DNA) encode protein structures.
      • DNA (deoxyribonucleic acid) characteristics include four nitrogenous bases:
      • Adenine
      • Cytosine
      • Guanine
      • Thymine
    • The sequence of these nitrogenous bases constitutes the genetic code.

  5. Metabolism

    • Living organisms sustain themselves by obtaining nutrients from their environments.
    • Metabolism encompasses two major processes:
      • Catabolism: Breaking down substances for energy.
      • Anabolism: Utilizing energy to construct cellular components.
    • The study of metabolism falls under physiology.

  6. Development

    • All organisms navigate through characteristic life cycles, often involving changes in size and shape.
    • Development varies:
      • Direct development: subtle changes
      • Indirect development: dramatic changes, such as those seen in metamorphosis.

  7. Environmental Interaction

    • All animals engage with their environments.
    • The study of such interactions is known as ecology.
    • Organisms exhibit irritability: responding to environmental stimuli.

  8. Movement

    • Living systems and their components demonstrate precise and controlled movements originating from internal processes.
    • Movement can refer to the organism as a whole or its individual parts.

A Not So Special Life

  • Life operates within the fundamental laws of the universe.
  • Historical view of vitalism (life's special nature) has been supplanted by an understanding towards universal physical laws.
  • Two core laws illustrated:
    1. 1st Law of Thermodynamics: Energy conservation
    2. 2nd Law of Thermodynamics: Entropy occurs naturally.

Principles of Science

  • Definition of Science: A method of knowing and question-asking about the world.
  • Essential principles of science:
    1. Guiding by natural law (physical and chemical laws).
    2. Explanatory through natural law references.
    3. Testable against observable phenomena.
    4. Conclusions are tentative and subject to change.
    5. Falsifiable: capable of being disproven.
  • Science is data-driven and relies on objective criteria as opposed to art or religion.
  • Scientific Method involves structured steps:
    1. Observation
    2. Question formulation
    3. Hypothesis development
    4. Empirical testing
    5. Conclusion drafting
    6. Dissemination of findings

Guiding Theories

  • Theory of Evolution by Natural Selection: Describes evolution as a process of change over time.
    • Natural selection is defined as descent with modification.
    • Best understood as consisting of five separate theories:

  1. Perpetual Change

    • Living world is never static or cycling.
    • Evidence sourced from fossil records, though incomplete and biased, confirms that the world undergoes constant change.

  2. Common Descent

    • All life forms descend from a common ancestor.
    • Supported by structural homologies and conserved DNA sequences.
    • Represented in phylogeny.

  3. Multiplication of Species

    • Evolution manifests as a branching process, transforming one species into two.
    • Leads to increased numbers of species over time.

  4. Gradualism

    • Major differences arise from the accumulation of small changes over extensive timeframes.

  5. Natural Selection

    • Variation exists among organisms.
    • Variation is partially heritable.
    • Not all variants reproduce successfully; those that do tend to leave a higher number of descendants, thus propagating favorable traits within populations.

Graphical Evidence of Natural Selection

  • Illustrations of species variations before, during, and after the industrial revolution exemplify changes in population traits:

    1. Prior to Industrial Revolution: Distribution rates of Light Morph and Dark Morph populations.
    2. During Industrial Revolution: Adjusted rates reflecting environmental changes on species.
    3. Environmental Cleanup Era: Changes in species population metrics post-environmental reforms.

Mendelian Heredity and the Chromosomal Theory of Inheritance

  • Gregor Mendel: Pioneered experiments using garden peas.
  • Methodology:
    • Crossed true-breeding populations.
    • Observed traits in successive offspring generations.
  • Key discoveries:
    • No blending of traits observed in generations; traits appear either as dominant or recessive rather than mixed (masking occurs).