BIO105 – Learning Guide Week 1: Nature of Science and Evolution Vocabulary
Science Vocabulary and Core Concepts
Science: systematic study of the natural world using evidence, observation, experimentation, and reasoning to build testable explanations.
Experiment: a controlled test that deliberately manipulates one or more factors to observe the effect on outcomes.
Observational study: study in which variables are observed as they occur in nature without deliberate manipulation; used to detect associations but not to prove causation.
Manipulative experiment: a study that deliberately changes one variable (the explanatory variable) to determine its effect on another variable (the response variable).
Scientific method: an iterative cycle of observation, formulation of a hypothesis, testing (experiments or observations), analysis, and revision; not a rigid step-by-step recipe but a flexible framework.
Observation: information gathered about the natural world using senses or instruments; foundation for forming hypotheses.
Variable: a quantity that can take on different values; in experiments, may be controlled, measured, or manipulated.
Explanatory variable (independent variable) $X$.
Response variable (dependent variable) $Y$.
Control: a condition kept constant to prevent it from influencing the outcome.
Matched variables: variables that are paired or matched across treatment groups to reduce confounding.
Correlation vs. causation: correlation is a statistical association between two variables; causation means one variable directly affects another. Correlation does not imply causation.
Fact: a claim supported by substantial, reproducible evidence.
Hypothesis: a testable, tentative explanation that can be falsified through observation or experiment.
Theory: a well-substantiated explanation of some aspect of the natural world that can incorporate laws, hypotheses, and verified patterns; contains:
Pattern: consistent observations or empirical regularities.
Process: mechanisms that explain how the pattern arises.
Law: a descriptive generalization about how some aspect of the natural world behaves under stated conditions, often with predictive power.
Evolution: heritable changes in populations over generations, leading to changes in traits and genetic composition over time.
Mechanisms of evolution: several processes that cause evolutionary change; the week emphasizes the following $5$ mechanisms:
a. Natural selection
b. Non-random mating (sexual selection)
c. Gene flow
d. Genetic drift
e. Mutation
Adaptation: a trait that increases an organism's fitness in a particular environment.
Selection: the differential reproductive success of individuals due to variation in traits.
Biological fitness: the contribution of an individual to future generations, often measured by the number of surviving offspring.
Concept Questions: open-ended prompts designed to provoke thought, recall, and application of concepts rather than testing for a single correct answer.
Key Concepts in Nature of Science and Evolution
Science aims to build robust explanations by testing predictions and refining theories in light of new evidence.
Observational studies are valuable for detecting natural correlations but must be interpreted cautiously regarding causality.
Manipulative experiments provide stronger tests of causal relationships by isolating the effect of an explanatory variable on a response variable.
Variables must be clearly defined and managed to avoid confounding and to enable replication.
The terms hypothesis, theory, and law serve different roles: hypotheses are testable explanations; theories are broad, well-supported frameworks; laws describe consistent natural relationships often expressed mathematically.
Evolution operates through multiple interacting mechanisms; understanding each helps explain both the unity and diversity of life.
Genetic variation arises from several sources; natural selection shapes which variants persist, leading to adaptation over generations.
Practical Concepts: Experimental Design and Explanation
Observational vs. manipulative design:
Observational study: identify and measure variables as they occur; assess associations and potential patterns.
Manipulative experiment: actively change an explanatory variable $X$ and observe the effect on the response variable $Y$ under controlled conditions; include appropriate controls.
Variables in a design:
Explanatory variable $X$ (independent variable) is what you manipulate to test effects.
Response variable $Y$ (dependent variable) is what you measure.
Control variables are kept constant to isolate the effect of $X$ on $Y$.
Matched variables are controlled by pairing or matching subjects to reduce confounding.
In infectious disease or medical practice contexts, think about how observational data can suggest hypotheses and how experiments can test them, e.g., comparing outcomes with different treatment regimens while controlling for confounders.
Evolution: Mechanisms, Examples, and Interactions
The five mechanisms of evolution (summary): $5$ mechanisms that cause allele frequencies to change over generations.
Natural selection: differential survival and reproduction favoring advantageous traits. Example: peppered moth color in polluted vs unpolluted environments.
Non-random mating (sexual selection): mate choice influences allele frequencies; features that improve mating success become more common.
Gene flow: migration between populations introduces new alleles or alters allele frequencies.
Genetic drift: random fluctuations in allele frequencies, especially in small populations (e.g., founder effects, bottlenecks).
Mutation: changes in DNA that create new alleles; source of novel genetic variation.
Adaptation and selection interplay:
Adaptations arise when existing genetic variation confers higher fitness in a given environment.
Selection acts on variation; over time, advantageous alleles increase in frequency.
Different environments can favor different adaptations; this leads to divergent evolution.
Examples to illustrate mechanisms:
Natural selection: antibiotic resistance in bacteria when exposed to antibiotics.
Sexual selection: elaborate plumage or courtship displays that improve mating success even if they reduce survival.
Gene flow: migration of pollinators or plants introducing new pollen alleles into a population.
Genetic drift: a small island population loses a trait simply by chance across generations.
Mutation: a new allele confers resistance to a toxin; if environment uses toxin, that allele increases in frequency.
Pattern vs. Process in evolution:
Pattern: what we observe—changes in allele frequencies, emergence of similar traits in distant lineages, etc.
Process: the mechanisms by which those patterns arise (natural selection, drift, gene flow, mating patterns, mutation).
Natural Selection and Genetic Variation: Core Questions
Ultimate source of all genetic variation:
The primary source is mutation, with recombination, gene duplication, and other genetic mechanisms contributing to new variants. In most texts, the canonical statement is that mutations introduce new genetic variation; recombination shuffles existing variation.
Expressed concisely: mutation is the ultimate source of novel variation; selection then acts on that variation.
How commonly would you expect adaptive variation to arise?
In large populations, new mutations occur more frequently, but most new alleles are neutral or deleterious; a small fraction are beneficial depending on the environment.
The likelihood that any single new mutation is adaptive is relatively low and context-dependent; over many generations, however, selection can rapidly increase the frequency of beneficial variants when they arise.
Do environmental conditions cause the ultimate source of variation to occur? Why or why not?
No: environmental conditions do not cause new mutations to arise in a directed way. Mutations occur largely at random with respect to environment (though some stress can influence mutation rates in certain organisms via stress-induced mutagenesis, this is not the primary driver of variation under normal conditions).
Environment selects among existing variants; it does not typically create them.
How does natural selection work if the environment doesn’t create new variation?
Natural selection acts on pre-existing variation in a population. Traits that confer higher fitness in a given environment become more common over generations as individuals bearing those traits leave more offspring.
Over time, this can lead to adaptation to local conditions and, with ongoing variation, to broader diversification.
Practical implications and real-world relevance:
Misunderstanding evolution can fuel misconceptions about purpose, design, or morality; clarifying that selection acts on variation and that mutations are not goal-directed helps counter such myths.
In medicine, understanding mechanisms of evolution informs strategies like antibiotic stewardship and vaccine design, where selective pressures shape microbial populations.
Conceptual Reflections and Academic Practice
Canvas and resource familiarity: know where to find guidelines, assignments, and learning resources; this supports efficient studying and timely completion of work.
Metacognition: reflecting on how you learn in class can help you study more effectively and save time—identify which study methods best reinforce these concepts.
Design thinking exercise: when given a topic (medical practice, education, evolution), design both an observational and a manipulative experiment; identify potential explanatory variables ($X$) and responses ($Y$), and consider controls and matching.
Scenario prompts to rehearse: explain how multiple evolutionary mechanisms can act simultaneously on a trait, and provide concrete examples where their effects overlap.
Summary takeaways for exam readiness:
Be comfortable defining each term and giving examples.
Distinguish between observational and manipulative experiments and identify appropriate variables.
Remember the five mechanisms of evolution and their core effects on populations.
Understand how natural selection uses existing variation to shape populations, and why mutations are essential for generating new variation.
Be able to discuss the interplay between pattern and process in scientific theories and to apply concepts to real-world contexts.
Quick Reference: Key Terms (cheat-sheet style)
Science
Experiment
Observational study
Manipulative experiment
Scientific method
Observation
Variable: $X$ (explanatory), $Y$ (response), Control, Matched variables
Correlation vs. causation
Fact, Hypothesis, Theory (Pattern, Process), Law
Evolution
Mechanisms of evolution: Natural selection, Non-random mating, Gene flow, Genetic drift, Mutation
Adaptation
Selection
Biological fitness
Examples and Practice Prompts (to simulate reasoning you should be able to do)
Observational vs. manipulative designs: propose a study on how education level affects test performance; which variables would you observe or manipulate, and what controls would you implement?
Five mechanisms with real-world examples:
Natural selection: pesticide resistance in pests when pesticides are used.
Non-random mating: male peacocks with larger tails mating more frequently.
Gene flow: birds migrating between populations introduce new alleles.
Genetic drift: a storm wipes out a subset of a small population, changing allele frequencies by chance.
Mutation: a random DNA change creates a new allele that affects a trait.
Natural selection and variation: imagine a population of bacteria under a new antibiotic; describe how mutation provides raw material and selection increases the frequency of resistant variants over time.
5 mechanisms of evolution involve different processes; remember that these can act in concert to shape populations across generations.