Ch 1
Principles of Life: Foundational Concepts in Biology
Introduction to Principles of Life
Organisms are characterized by their ability to capture and transform energy, pass genetic information, grow, develop, behave, and interact with the environment.
Most energy vital for sustaining life originates from the Sun.
Plants, such as grasses and trees, possess chlorophyll, a green pigment that absorbs solar light energy.
Some plants, like the acacia tree, have evolved specific shapes (e.g., numerous leaves presented to the Sun) to maximize solar energy absorption and evade herbivores.
Through photosynthesis, green leaves convert water and carbon dioxide into sugar and oxygen, storing solar energy in the sugar.
Plants utilize this sugar for energy to build tissues and grow.
Animals, such as giraffes, consume plants to acquire this stored energy, making them (and indirectly humans) "solar-powered."
Beyond energy flow, living organisms exhibit complex interactions and undergo evolution based on interaction demands.
The long neck of giraffes, evolving over millions of years, exemplifies an adaptation allowing them to access high tree leaves within their ecosystem.
Key Concepts in Biology
Living Organisms Share Common Aspects of Structure, Function, and Energy Flow.
Life Depends on Organization and Energy.
Genetic Systems Control the Flow, Exchange, Storage, and Use of Information.
Evolution Explains the Diversity as Well as the Unity of Life.
Science Is Based on Quantitative Observations, Experiments, and Reasoning.
1.1 Living Organisms Share Common Aspects of Structure, Function, and Energy Flow
Biology Defined: The scientific study of life, encompassing all living things, or organisms.
Single Origin of Life: All known life on Earth is believed to be descended from a single-celled ancestor that lived approximately 4 billion years ago.
This concept is supported by overwhelming evidence of shared characteristics among living organisms.
Shared Characteristics of Living Organisms: Consistent traits pointing to common ancestry:
Composed of a common set of chemical parts, including nucleic acids (like DNA for genetic information) and amino acids (protein building blocks).
Microscopically, they consist of similar structures, such as cells encased within membranes.
Depend on intricate interactions between structurally complex parts to maintain a living state.
Contain genetic information utilizing a nearly universal code for protein assembly.
Convert molecules from their environment into new biological molecules.
Extract energy from the environment to perform life functions.
Replicate their genetic information in a similar manner during reproduction.
Possess a fundamental set of genes with structural similarities.
Evolve through gradual changes in their genetic information.
Implications of Common Ancestry: If life originated multiple times, such universalities (genetic code, gene similarities, common amino acids) would be unlikely.
Example: A hypothetical self-replicating system on another planet might use genetic information but would likely have fundamentally different codes and chemical building blocks.
Diversity and Unity: While life exhibits fundamental unity stemming from a common ancestor, there is also enormous diversity (e.g., myriad bird and tree species).
Understanding the evolution of this diversity is a central question in biology.
Boundaries of "Living" vs. "Non-living": These boundaries are not always clear.
Viruses present a key debate: They are not cellular, cannot perform most functions independently (rely on host cells), but contain genetic information, mutate, and evolve.
Most biologists consider viruses a part of life due to their genetic nature and strong evidence of evolving from cellular life forms, even if they are not independent cellular organisms.
Major Steps in the History of Life
Earth's Formation: Geologists estimate Earth formed between 4.6 and 4.5 billion years ago.
Earliest Life: Life evolved at least 600 million years after Earth's formation.
Life's Calendar Analogy (Figure 1.1): Representing Earth's history as a 30-day month (where 1 day = approximately 150 million years):
Day 5: Life first appeared (less than 4 billion years ago).
Day 13: Photosynthesis evolved (approximately 2.5 billion years ago), changing the nature of life.
Day 20: Eukaryotic cells evolved (approximately 2.5 billion years after life originated).
Day 26: Multicellular organisms appeared.
Day 27: First land plants.
Day 28: Coal-forming forests, ozone layer developed sufficiently (around 500 million years ago), allowing life to move onto land.
Day 29: First birds.
Day 30 (last 5 minutes): Homo sapiens (modern humans) arose (around 500,000 years ago).
Day 30 (last few seconds): Recorded history.
Origin from Nonliving Matter: Early Earth's conditions (atmosphere, oceans, climate) were different.
Experiments simulating early Earth confirm the possible, even probable, formation of complex organic molecules.
The critical evolutionary step was the appearance of nucleic acids (self-replicating molecules containing information for synthesizing other large, stable molecules).
These large molecules were proteins, whose varied shapes enabled participation in diverse chemical reactions.
Cellular Structure Evolved in the Common Ancestor of Life
The next significant step was the encapsulation of complex proteins and other biological molecules within a membrane, forming a tiny cell.
Fatty acids played a key role; they form membrane-like films that, when agitated, create hollow spheres capable of enveloping biological molecules.
This separation of internal components from the external environment allowed reactants and products of chemical reactions to be concentrated, integrated, and controlled.
This natural process led to the first cellular organisms capable of reproduction.
Prokaryotes: For over 2 billion years after cell origin, all organisms were single-celled prokaryotes.
Prokaryotes consist of a single cell with genetic material and biochemical structures enclosed by a membrane, lacking a nucleus (e.g., bacteria like Haloferax mediterranei).
Early prokaryotes thrived in oceans, using abundant molecules for raw materials and energy, and being shielded from intense UV light due to a lack of atmospheric oxygen (O2) and ozone (O3).
Photosynthesis Allowed Living Organisms to Capture the Sun's Energy
Early Energy Acquisition: The earliest prokaryotes obtained energy by breaking down molecules directly from their environment.
Emergence of Photosynthesis: Around 2.5 billion years ago (Day 13 on Life's Calendar), some prokaryotes evolved photosynthesis.
Definition: A set of chemical reactions transforming sunlight energy into chemical-bond energy stored in sugar (glucose) and other small biological molecules.
Purpose: This chemical-bond energy powers other cellular reactions, including the synthesis of large molecules like proteins.
Ecological Significance: Photosynthesis forms the base of the food web, providing energy for photosynthetic organisms and those that consume them (e.g., plants and giraffes).
Early photosynthetic cells were likely cyanobacteria (Figure 1.3), known from ancient stromatolite fossils and living examples.
The Impact of Oxygen (O_2):
The byproduct of photosynthesis, O_2, accumulated in the atmosphere, initially being poisonous to many prokaryotes.
Organisms that tolerated O_2 proliferated, opening new evolutionary pathways.
Aerobic metabolism (using O2) proved more efficient for energy release than anaerobic metabolism (without O2), allowing organisms to grow larger and live more intensely.
The majority of living organisms today use O_2 for energy extraction.
Movement onto Land: The O2 accumulation over more than 2 billion years led to the formation of a protective ozone (O3) layer in the upper atmosphere.
By about 500 million years ago (Day 28), the ozone layer was dense enough to shield Earth's surface from destructive UV radiation, enabling life to colonize land.
Eukaryotic Cells Arose Through Endosymbiosis
Organelles: An earlier significant step was the evolution of cells with internal membrane-enclosed compartments (organelles) where specialized cellular functions could occur.
First organelles appeared around 2.5 billion years after life, or on Day 20 of Life's Calendar.
The nucleus (from Latin nux, "nut" or "core") contains the cell's genetic information, defining eukaryotes (Greek eu, "true," + karyon, "kernel" or "core").
Prokaryotes (Greek pro, "before") lack nuclei.
Endosymbiosis Hypothesis: "Living inside another," where larger cells engulfed smaller ones, leading to stable partnerships.
Mitochondria (energy release): Are believed to have evolved from engulfed prokaryotic organisms.
Chloroplasts (photosynthesis): Are hypothesized to have originated when larger eukaryotes ingested photosynthetic prokaryotes.
These ingested cells provided functions (e.g., sugars from photosynthesis) in return for a protective environment.
Multicellularity Allowed Specialization of Tissues and Functions
For the first few billion years, all organisms (prokaryotic or eukaryotic) were single-celled.
Origin of Multicellularity: In some eukaryotes, cells failed to separate after division, remaining attached.
This allowed for cell specialization (e.g., some cells for reproduction, others for nutrient absorption).
Benefits: Increased organism size and enhanced efficiency in resource gathering and adapting to specific environments.
Biologists Can Trace the Evolutionary Tree of Life
All Earth's organisms descend from a single unicellular ancestor, raising the question of how such diversity arose.
Genome and Mutation: Organisms reproduce by replicating their genome (total genetic material).
This replication is imperfect, introducing changes called mutations.
Mutations can lead to structural and functional changes that spread within a population.
Speciation: If populations are isolated, structural and functional differences accumulate, eventually preventing regular interbreeding, leading to new species.
Tens of millions of species exist today; many more are extinct.
Binomial Nomenclature: Each species receives a scientific name (e.g., Homo sapiens).
The first word is the genus (group of species with a recent common ancestor); the second is the species name.
Scientific names are italicized, universal, and distinct from common names (e.g., Homo is Latin for "man," sapiens for "wise" or "rational").
Comparative Genomics: Recent advances in genome sequencing (determining nucleotide order in DNA) allow comparisons of genetic information across species.
This provides molecular evidence that complements knowledge from the fossil record.
Enables the compilation of phylogenetic trees, which map evolutionary relationships (Figure 1.4).
Tree of Life Domains: The broad outlines of the Tree of Life show:
Two major branches: Bacteria and Archaea (prokaryotes).
Eukarya: A specialized group stemming from Archaea, having acquired mitochondria and chloroplasts from endosymbiotic bacteria, and possessing a distinct nucleus.
Thus, three domains of life: Bacteria, Archaea, and Eukarya. Approximately 1.3 million animal species, 270,000 plant species, and 100,000 fungi species are estimated to be known (described).
Multicellularity in Eukarya: Arose independently in several groups (plants, brown algae, fungi, animals), each closely related to different groups of unicellular eukaryotes (protists).
Unity Generalizes Discoveries: The common ancestry, shared genetic code, and similar molecular building blocks of all life mean that discoveries in one organism can often be generalized to others.
Model Systems: Specific species used for research, with findings extended to humans and other organisms.
Bacterial research illuminated basic cellular chemical reactions.
Chlorella (unicellular green alga) research clarified photosynthesis biochemistry.
Arabidopsis thaliana (mustard family) informed plant development genes.
Sea urchins, frogs, chickens, roundworms, and fruit flies contributed to understanding animal development.
Zebrafish research led to the discovery of a major human skin color gene.
1.2 Life Depends on Organization and Energy
Second Law of Thermodynamics: Organized entities naturally tend towards increased randomness or disorganization.
Energy for Organization: Organisms, particularly cells, must continually expend energy to counteract this thermodynamic tendency and maintain their complex organization.
Organization in a Hierarchy of Levels
Internal Hierarchy (Figure 1.5A): Cells actively synthesize complex molecules (e.g., proteins) from atoms, arranging them into highly organized structures.
Example: Fatty acids form membranes that compartmentalize cells; proteins act as catalysts for specific chemical reactions.
In multicellular organisms, cells specialize and cooperate.
Specialized cells depend on others, necessitating systems like a circulatory system to connect functions across the body.
Levels: Atoms → Small molecules (water, oxygen, methane, carbon, hydrogen) → Large molecules (DNA, proteins) → Cells → Cell specialization → Colonial organisms → Tissues → Organs → Organ Systems → Organism (e.g., leopard frog).
All these internal organizational levels require continuous energy input to prevent degradation.
External Hierarchy (Ecosystems) (Figure 1.5B): Organisms interact with each other and their physical environment.
Levels: Individual Organisms → Populations (groups of one species) → Communities (interacting populations of multiple species) → Landscapes (multiple communities) → Biosphere (the total of Earth's life and landscapes).
Distinction Between Hierarchies:
Internal: Encoded by a single genome, leading to generally harmonious interactions.
External: Involves multiple species and genomes; interactions are not always harmonious (e.g., competition, predation).
Each Level of Biological Organization Consists of Systems
Definition of a System: A set of interacting parts where understanding requires considering the interactions.
Components (e.g., proteins, nutrients, organisms) and processes (e.g., protein synthesis, metabolism, grazing) define a system (Figure 1.6).
Examples of Systems (Figure 1.7):
(A) Cellular-level: System for synthesizing and controlling the quantity of a protein (Protein T), involving amino acids, Protein T, breakdown products, synthesis, and breakdown pathways.
(B) Organismal-level: Physiological system regulating sodium (Na^+) in body fluids, involving absorption from food, gut cells, kidney excretion, and amounts of Na^+ in various compartments.
(C) Community-level: System determining vole populations, involving grass abundance, vole consumption of grass, and predation by foxes and owls.
Biological Systems Are Highly Dynamic yet Maintain Organization
Biological systems are characterized by rapid flows of matter and energy.
Example: An average cell breaks down and rebuilds 2-3 percent of its proteins daily.
It produces and uses over 100,000 trillion (10^{14}) molecules of adenosine triphosphate (ATP) daily for energy shuttling.
Your cells liberate over 90 grams of hydrogen from food and synthesize almost 1 liter of water daily by combining hydrogen with oxygen.
Organisms constantly exchange matter and energy with their surroundings, with molecules continually replaced, yet their overall organization persists.
Positive and Negative Feedback Are Common in Biological Systems
Feedback: Occurs when a product of a system affects the rate of an earlier process (Figure 1.8).
Positive Feedback: A product speeds up an earlier process, leading to accelerated production of that product.
Tends to destabilize a system, but can be advantageous if ultimately controlled.
Negative Feedback: A product slows down an earlier process in the system.
Increases in product concentration lead to greater slowing effects, thereby stabilizing the product's amount.
Very common in regulatory systems that maintain stable amounts or concentrations.
Systems Analysis as a Conceptual Tool
Systems Analysis: An approach used by biologists to understand biological system function, involving:
Identifying components and specifying interaction processes (Figure 1.6).
Quantifying interaction rates and how they are affected by feedback.
Analyzing system changes over time (increase/decrease, stability, equilibrium).
Mathematical Modeling: Involves writing mathematical equations to express component amounts, processes, and rates (Figure 1.9).
Example: Amount of B at future time = Amount of B now + Amount of A converted to B - Amount of B converted to C.
Computational models, often requiring computers for large systems, mimic biological systems.
Prediction: A key use of computational models is to develop hypothetical predictions, such as the future behavior of a biological system in a warming world by adjusting for expected atmospheric temperature increases.
1.3 Genetic Systems Control the Flow, Exchange, Storage, and Use of Information
Genome: The complete "blueprint" for an organism's existence, comprising all information encoded by its genes.
Genetic information and its decoding into proteins (which form structure and function) are fundamental biological principles.
Genomes Encode the Proteins That Govern an Organism's Structure
Nucleic Acids: Self-replicating molecules (like DNA) composed of long sequences of four nucleotides (C, G, T, A).
The specific nucleotide sequence in DNA (deoxyribonucleic acid) dictates how an organism assembles proteins (Figure 1.10).
A gene is a specific DNA segment carrying information for building one or more proteins.
Proteins: Molecules that govern cellular chemical reactions and form much of an organism's structure; thus, genes are said to "encode" proteins.
Scale of Genetic Information: The human genome contains over 3 billion nucleotide letters, which would fill more than 1,000 books the size of this one.
Cellular Differentiation: All cells in a multicellular organism share the same genome, but different cell types express different parts of the genome (e.g., red blood cells produce hemoglobin; gut cells produce digestive proteins).
Mutations: Changes in the nucleotide sequence of a gene can alter the protein it encodes.
Causes: Spontaneous errors during DNA replication, chemical exposure (e.g., cigarette smoke), or radiation (e.g., UV light).
Effects: Most mutations are harmful or have no effect; occasionally, one improves an organism's function under specific environmental conditions.
Raw Material for Evolution: Natural selection can favor the persistence of beneficial mutations, making mutations the fundamental source of evolutionary change.
Genomes Provide Insights into All Aspects of an Organism's Biology
History of Genome Sequencing:
First complete pathogen genome sequenced: virus (in 1976).
First bacterial genome sequenced: 1995.
First animal genome (roundworm) sequenced: 1998.
Human Genome Project: 1990 - 2003.
Impact of Sequencing: Thousands of species sequenced since, with rapidly decreasing costs and time due to new technologies.
Surprising Discoveries: Some genomes contained fewer genes than anticipated (e.g., the human genome has only about 20,000 protein-coding genes).
Comparative Genomic Studies: Comparing genomes across species helps biologists understand differences, trace gene evolution, and link genetic changes to structural/functional variations (e.g., inherited diseases).
Bioinformatics: The field dedicated to the organization and use of biological information, involving biologists and computer scientists developing tools to manage and analyze massive genomic databases.
1.4 Evolution Explains the Diversity as Well as the Unity of Life
Evolution Defined: Change in the genetic makeup of biological populations over time, a major unifying principle of biology.
Evolutionary Processes: Any process causing changes in gene frequencies across generations. These processes drive the diversity of life while maintaining fundamental unity.
Natural Selection Is an Important Process of Evolution
Charles Darwin: In On the Origin of Species (1859), he presented evidence for evolution (descent from common ancestor) and identified natural selection as a key process.
Darwin's Reasoning (without modern genetics):
Offspring show variation from parents despite similarities.
Populations exhibit individual variation.
Artificial Selection: Humans select for specific traits in breeding (e.g., pigeons) to produce desired offspring.
Natural Selection: A similar process occurs in nature, where "selection" is driven by differential survival and reproductive success, with some individuals contributing more offspring to future generations.
Mechanism of Natural Selection:
Unchecked reproductive capacities would lead to unlimited population growth, which is not observed.
Only a small percentage of offspring survive to reproduce.
Any trait increasing an organism's probability of survival and reproduction, even slightly, will spread in the population.
Adaptations: Traits (structural, physiological, or behavioral) that increase an organism's chances of surviving and reproducing in its specific environment. Adaptations are a direct result of natural selection.
Frog Adaptations (Figure 1.11):
Tree frogs: Expanded toe pads for climbing.
Aquatic frogs: Webbed rear feet for swimming.
Ground-living frogs: Short legs, peg-like digits for walking.
Gliding tree frogs: Extended webbing for gliding between trees.
Explanations for Adaptations:
Proximate Explanations: Focus on how an adaptation works (e.g., the physical structure of toe pads and how they adhere).
Ultimate Explanations: Focus on the evolutionary processes that led to the adaptation (e.g., comparing variation among species to understand how a trait affects survival/reproduction).
Other Evolutionary Processes: Natural selection is not the only mechanism of evolution.
Genetic drift: Random changes in gene frequencies in a population due to chance events.
All biological populations evolve over time, leading to Earth's remarkable diversity.
Evolution Is a Fact, as well as the Basis for Broader Theory
Theodosius Dobzhansky: Emphasized that "Nothing in biology makes sense except in the light of evolution," highlighting its central role in biological understanding.
Understanding "Theory" in Science: The common misconception that evolution is "just a theory" stems from different meanings of the word.
Everyday use: "Theory" often means a hypothesis or guess.
Scientific use: A "theory" is a rigorously tested, well-established body of facts and principles used to make predictions about the natural world.
Evolution as a Fact: The occurrence of evolution in biological populations is factually observable and measurable.
Direct Observation: Changes in genetic makeup can be observed over short periods (e.g., influenza viruses evolve quickly, necessitating annual flu vaccines).
Historical Record: The fossil record provides direct evidence of evolution's long history.
Testability: How populations change is subject to testing and experimentation.
The fact that biological populations evolve is universally accepted among biologists.
1.5 Science Is Based on Quantitative Observations, Experiments, and Reasoning
Core of Scientific Investigation: All scientific endeavors rely on quantitative observation, experimentation, and reasoning, guided by established methodological principles.
Observing and Quantifying Are Important Skills
Observation: Biologists are driven by observing the living world.
Understanding the natural history of organisms (food, reproduction, behavior, regulation, interactions) enhances observation and prompts questions.
Knowledge of general life principles leads to new insights from nature.
Enhanced Observation Technologies: Technologies like electron microscopes, rapid genome sequencing, magnetic resonance imaging, and GPS satellites extend observational capabilities from molecular distributions to animal movements.
Quantification: Observations must be quantified into explicit counts or measures that can be used and verified.
Progress in quantification (e.g., molecular/physical differences vs. qualitative descriptions) combined with mathematical models allows quantitative analysis of evolutionary history.
Scientific Methods Combine Observation, Experimentation, and Logic
The "scientific method" is not a rigid, linear process; scientists may begin at various points.
Hypothesis-Prediction Method (5 Steps) (Figure 1.12):
Make observations.
Ask a question.
Formulate alternative hypotheses (possible answers to the question).
Make predictions (what else should be true if each hypothesis is correct).
Design and conduct an experiment to test one of the predictions.
Coral Reef Bleaching Example:
Observation: Reef-building corals have shapes similar to acacia trees.
Question: Why? (Figure 1.13)
Explanation: Corals are animals collaborating in a symbiosis with photosynthetic algae (zooxanthellae) living within their tissues. Algae produce sugars, providing much energy for the coral. Coral shapes maximize light capture for these symbiotic algae.
Problem: Widespread coral reef "bleaching" events (loss of pigmentation, pale/white coral, weakening, death) observed since about 70 years ago, now more frequent.
Bleaching Mechanism: Disruption of the coral-alga symbiosis, where corals lose symbionts or symbionts lose pigments, depriving corals of food.
Hypotheses for Bleaching Causes: Various environmental stresses (pollution, freshwater runoff, changing climate, increased temperature, ocean acidity) were initially implicated, but specific causes were unclear due to simultaneous occurrences.
Hoegh-Guldberg and Smith's Controlled Experiment (1989):
Location: Lizard Island Research Station, Great Barrier Reef.
Species: Stylophora pistillata and Seriatopora hystrix.
Method: Maintained healthy corals in laboratory aquaria at 27^ ext{o} ext{C} under 25 ext{%} full sunlight.
High-light treatment: Exposure to full sunlight (constant 27^ ext{o} ext{C}).
High-temperature treatment: Water temperature raised to 32^ ext{o} ext{C} (25 ext{%} sunlight).
Results: Both high light and high temperature caused bleaching.
High light caused algal symbionts to lose pigmentation (chlorophyll a levels decreased in algae, while algal cell counts remained stable).
High temperatures caused corals to lose their algae completely (algal cell counts decreased).
Conclusion: Both stresses disrupt the symbiosis, demonstrating that excessive warm water temperatures alone could cause bleaching. (Results show a decrease in chlorophyll content of coral, decrease in zooxanthellae per cm^2 in high temperature, stable zooxanthellae in high light but decreased chlorophyll a per cell).
Terry Hughes et al.'s Comparative Experiment (1998, 2002, 2016):
Location: Extensive study across the Great Barrier Reef (2,300 kilometers long, containing about 600 coral species, with varied conditions).
Method: Used satellite imagery to map sea surface temperatures (in Degree Heating Weeks, a unit combining excess heat and duration) and aerial surveys to assess bleaching severity (percentage of bleached reef area) at hundreds of sites (638 sites in 1998, 631 in 2002, and 1,156 in 2016).
Results: Found a strong correlation between water temperature and bleaching severity across the Great Barrier Reef, validating the lab findings in a natural context. Ocean heating correctly predicted bleaching at 75 ext{%} of sites.
Conclusion: Ocean temperature is a reliable global predictor of bleaching, indicating a grave threat from ocean warming. Ongoing research focuses on coral resistance and recovery.
Well-designed Experiments Have the Potential to Falsify Hypotheses
Falsifiability: The most informative experiments are designed to potentially prove a prediction wrong.
If a prediction is falsified, the hypothesis must be modified or rejected.
Types of Experiments:
Controlled Experiment: Deliberately manipulates one or more independent variables (factors being tested) and compares an experimental group (manipulated) with a control group (unmanipulated), while keeping all other variables constant. Measures a dependent variable (the response).
Example: Hoegh-Guldberg and Smith's laboratory experiments on coral (INVESTIGATION FIGURE 1.14 details independent variables like light/temperature, and dependent variables like chlorophyll content in ext{µg/cm}^2, zooxanthellae count in 10^6 ext{ cells/cm}^2, and chlorophyll a in zooxanthellae in ext{pg/cell}).
Comparative Experiment: Compares unmanipulated data from naturally existing groups based on a hypothesis. Variables are not controlled or manipulated, and not all variables may be identifiable.
Example: Hughes et al.'s extensive field study on the Great Barrier Reef, correlating natural temperature variations with bleaching severity (INVESTIGATION FIGURE 1.15).
Iterative Process: Scientific inquiry is open-ended; experimental results often raise new questions, leading to further hypotheses and experiments, continuously improving understanding.
Statistical Methods Are Essential Scientific Tools
Purpose: To objectively determine if observed differences (e.g., between experimental groups) are real or merely due to chance.
Statistical Significance: The extent to which a result is unlikely to be due to chance alone.
Addressing Variation: Scientists use statistics because variation is inherent in measurements.
Statistical Tests: Calculate the probability that observed differences could arise from random variation.
Begin with a null hypothesis: The premise that observed differences are purely due to random variation between samples from the same population.
Scientists calculate the probability of obtaining their data if the null hypothesis is correct; the goal is to make it unlikely that observed differences are due to chance.
Not All Forms of Inquiry into Nature Are Scientific
Defining Science: Science is a human endeavor characterized by specific standards: objectivity, dependence on evidence, testable and falsifiable hypotheses.
Methods must be clearly described for reproducibility and independent verification.
Distinguishing Science from Non-Science:
Art, music, literature: Contribute to human life quality but do not use scientific methods to establish facts.
Religion: Historically explained natural phenomena (weather, disease), but most are now scientifically explained.
Religious tenets (e.g., existence of deities) are beyond the realm of science because they cannot be confirmed or refuted experimentally.
Scientific power comes from reproducible, quantifiable observations and testable hypotheses.
Supernatural explanations (e.g., a "creator") are untestable and thus outside science.
Science's Scope: Science describes "how the world works" but is silent on "how the world ought to be."
Ethical Implications: Scientific advances (e.g., in genetics for sex selection, stem cells, genome modification) raise profound ethical questions.
Science provides the capability but cannot dictate whether these actions should be taken or how they should be regulated.
Responsible scientists acknowledge these ethical questions and the contributions of humanities in addressing them.
Big Themes: Throughout biology, fundamental principles like evolution are recurring themes, explored from molecular organization to ecosystems.