Chapter 1: Life: Biological Principles and the Science of Zoology

1.1: Fundamental Properties of Life

• Zoology: The scientific study of animal life, builds on centuries of human observations of the animal world.
• Life’s most fundamental attribute is its reproduction of individuals with heredity and variation.
• Evolution: A temporal continuity of ancestral and descendant populations showing extensive and ongoing change.

General Properties of Living Systems

• Chemical uniqueness
  • Living systems demonstrate a unique and complex molecular organization.
  • Macromolecules: Large molecules which the living things assemble. It contains the same kinds of atoms and chemical bonds that occur in nonliving matter and obey all fundamental laws of chemistry.
• Complexity and hierarchical organization
  • Living systems demonstrate a unique and complex hierarchical organization.
  • Emergence: Appearance of new characteristics at a given level of organization.
  • Emergent Properties: These properties arise from interactions among the component parts of a system.
• Reproduction
  • Living systems can reproduce themselves.
  • Heredity: The faithful transmission of traits from parents to offspring, usually observed at the organismal level.
  • Variation: The production of differences among the traits of different individuals.
• Possession of a genetic program
  • A genetic program provides fidelity of inheritance.
  • Nucleic acids: Encode structures of the protein molecules needed for organismal development and functioning.
  • DNA: Stores genetic information.
  • Genetic Code: The sequence of amino acids in a protein.
• Metabolism
  • Living organisms maintain themselves by acquiring nutrients from their environments.
  • Nutrients supply the chemical energy and molecular components for building and maintaining a living system.
  • Physiology: The study of metabolic functions from the biochemical to the organismal levels.
• Development
  • All organisms pass through a characteristic life cycle.
  • Development describes the characteristic changes that an organism undergoes from its origin to its final adult form.
  • Metamorphosis: The transformation that occurs from one stage to another.
• Environmental interaction
  • All animals interact with their environments.
  • Ecology: The study of organismal interaction with an environment.
  • Irritability: A property where all organisms respond to environmental stimuli.
• Movement
  • Living systems and their parts show precise and controlled movements arising from within the system.
  • The energy that living systems extract from their environments permits them to initiate controlled movements.

Life Obeys Physical Laws

• Thermodynamics: Laws governing energy and its transformations.
• First Law of Thermodynamics: Law of Conservation of Energy
  • Energy is neither created nor destroyed but can be transformed from one form to another.
• Second Law of Thermodynamics: Any spontaneously occurring process will always lead to an escalation in the entropy of the universe.

1.2: Zoology as Part of Biology

• Animals form a distinct branch on the evolutionary tree of life.
• It is a large and old branch that originated in the Precambrian seas over 600 million years ago.
• Eukaryotes: Those animals that form part of an even larger limb; organisms whose cells contain membrane-enclosed nuclei.
  • It includes plants, fungi, and numerous unicellular forms.
• We distinguish animals also by the absence of characteristics that have evolved in other eukaryotes but not in animals.
  • Plants have photosynthesis and cell walls.
  • Fungi acquire nutrition by absorption of small organic molecules from their environments.
  • Euglena: It is a motile, single-celled organism that resembles plants in being photosynthetic, but resembles animals in its ability to eat food particles.
• Microbiome: A major characteristic of animal life that is often overlooked: animal bodies typically harbor thousands of species of bacteria and archaea, primarily in the gut.
  • It influences our digestion of food, and variation in the content of the microbiome among individuals can influence our body weight and susceptibility to malnutrition
  • It is not essential for the survival of humans or mice but is critical to the survival of other species.

1.3: Principles of Science

Nature of Science

• Science: A way of asking questions about the natural world and sometimes obtaining precise answers to them.
• Essential Characteristics of Science:
  • It is guided by natural law.
  • It has to be explanatory by reference to natural law.
  • It is testable against the observable world.
  • Its conclusions are tentative and therefore not necessarily the final word.
  • It is falsifiable.
• Scientific knowledge must explain what is observed by reference to natural law without requiring the intervention of a supernatural being or force.
• Pursuit of scientific knowledge must be guided by the physical and chemical laws that govern the state of existence.
• While anybody is free to approach a scientific inquiry in any fashion they choose, they cannot properly describe the methodology used as scientific if they start with a conclusion and refuse to change it regardless of the evidence developed during the course of the investigation. — Judge Overton.
• Science lies outside religion, and the results of science do not favor one religious position over another.

Scientific Method

• Hypothetico-Deductive Method: This method requires us to generate hypotheses or potential answers to a question being asked.
  • These hypotheses are usually based on prior observations of nature or derived from theories based on such observations.
• Scientific hypotheses often constitute general statements about nature that may explain a large number of diverse observations.
• Darwin’s hypothesis of natural selection: Explains the observations that many different species have properties that adapt them to their environments.
• The scientific method is summarized as a series of steps:
  • Observation
  • Question
  • Hypothesis
  • Empirical Test
  • Conclusions
  • Publication
• Null Hypothesis: The one that permits a statistical test of our data to reject its predictions if the hypothesis is false.
• If a hypothesis is very powerful in explaining a wide variety of related phenomena, it attains the status of a theory.
• If my hypothesis is a valid explanation of past observations, then future observations ought to have certain characteristics.
• Paradigms: Powerful theories that guide extensive research.
  • Darwin’s theories led to a scientific revolution that replaced these views with the evolutionary paradigm.
  • Evolutionary theory is generally accepted as the cornerstone of biology.

Experimental Versus Comparative Methods

• The first category seeks to explain the proximate or immediate causes that underlie the operation of biological systems at a particular time and place.
  • Hypotheses of proximate causes are tested using the experimental method.
  • Controls: Repetitions of the experimental procedure that lack the treatment; eliminate the unknown factors that might bias the outcome of the experiment.
• The second category is the questions of the ultimate causes that have produced these systems and their distinctive characteristics through evolutionary time.
  • Tests of hypotheses of ultimate causality require the comparative method.
  • The method often relies on the results of experimental sciences as a starting point. It applies to all levels of biological complexity.
  • Teleology: The mistaken notion that the evolution of living organisms is guided by purpose toward an optimal design.

1.4: Theories of Evolution and Heredity

Darwin’s Theory of Evolution

1. Perpetual change: It states that the living world is neither constant nor perpetually cycling, but is always changing, with continuity between past and present forms of life.

   • The basic theory of evolution on which the others depend.

2. Common descent: It states that all forms of life descend from a common ancestor through a branching of lineages.

   • Phylogeny: The relationship between all the organisms on Earth that have descended from a common ancestor, whether they are extinct or extant.

3. Multiplication of species: It states that the evolutionary process produces new species by splitting and transforming older ones.

4. Gradualism: It states that the large differences in anatomical traits that characterize disparate species originate through the accumulation of many small incremental changes over very long periods of time.

   • This theory is important because genetic changes that have very large effects on organismal form are usually harmful to an organism.

5. Natural selection

   • Darwin’s most popular theory that rests on three propositions:
   1. There is variation among organisms for anatomical, behavioral, and physiological traits.
   2. The variation is at least partly heritable so that offspring tend to resemble their parents.
   3. Organisms with different variant forms are expected to leave different numbers of offspring to future generations.

• Adaptation: A phenomenon wherein natural selection explains why organisms are constructed to meet the demands of their environment.
• Particulate Inheritance: A pattern of inheritance showing that phenotypic traits can be passed from generation to generation through genes, which can keep their ability to be expressed while not always appearing in a descending generation.
• Chromosomal Theory of Inheritance: States that chromosomes are the vehicles of genetic heredity.
• Neo-Darwinism: A modified theory of Darwinism explaining the origin of species on a genetic basis.

Mendelian Heredity and the Chromosomal Theory of Inheritance

• Chromosomal Theory of Inheritance: This theory comes from the consolidation of research done in the fields of genetics, which was founded by the experimental work of Gregor Mendel, and cell biology.
• Genetic Approach: It consists of mating or “crossing” populations of organisms that are true-breeding for contrasting traits, and then following hereditary transmission of those traits through subsequent generations.
• True Breeding: Means that a population maintains across generations only one of the contrasting traits when propagated in isolation from other populations.
• Cell Biology
  • As the precursors of gametes prepare to divide early in gamete production, the nuclear material condenses to reveal discrete, elongate structures called chromosomes.
  • Chromosomes occur in pairs that are usually similar but not identical in appearance and informational content.
  • Paired chromosomes are physically associated and then segregated into different daughter cells during cell division prior to gamete formation.