Difficulty: Introductory | Prerequisites: None. This is foundational material for the entire course.
Science works by forming testable hypotheses, running controlled experiments, and revising ideas when the data say so. Every organism gets a standardised two-part Latin name so biologists worldwide can talk about the same species without confusion. Darwin's theory of evolution by natural selection explains how populations change over time: individuals with traits that improve survival and reproduction pass those traits on, gradually reshaping the genetic makeup of the population.
Hypothesis
A testable, falsifiable statement predicting the outcome of an observation or experiment. Think of it as an educated guess that can be proven wrong.
Scientific theory
A well-substantiated explanation of natural phenomena, supported by extensive evidence and widely accepted by the scientific community. In simple terms, this means a hypothesis that has survived rigorous testing over many years and now explains a broad range of observations.
Independent variable
The factor the researcher deliberately changes (manipulates) in an experiment. Think of it as the thing you are testing.
Dependent variable
The factor being measured in an experiment, the outcome that may change in response to the independent variable. In simple terms, this is the result you observe.
Control group
The group in an experiment that is not exposed to the independent variable, serving as a baseline for comparison.
Binomial nomenclature
The two-part Latin naming system for organisms, consisting of the genus (capitalised) and specific epithet (lowercase), established by Carl Linnaeus. Think of it as every species' official first and last name.
Genus
The first part of a scientific name, capitalised and italicised, grouping closely related species together.
Specific epithet
The second part of a scientific name, lowercase and italicised, identifying a particular species within its genus.
Dichotomous key
A tool for identifying organisms by working through a series of paired yes/no questions about observable traits.
Phylogenetic tree
A branching diagram that shows the evolutionary relationships and lineage among groups of organisms. Think of it as a family tree for species.
Natural selection
The process by which organisms with traits better suited to their environment tend to survive and reproduce more successfully, passing those traits to the next generation. In simple terms, "survival of the fittest" where "fittest" means best-adapted, not strongest.
Adaptation
A heritable trait that increases an organism's fitness in a given environment.
Fitness (biological)
An organism's reproductive output relative to others in the population. In simple terms, how many viable offspring you leave behind, not how strong you are.
Gradualism
The idea that large evolutionary changes result from the accumulation of small, incremental changes over long periods.
Common descent
The principle that all living organisms share a common ancestor and have diverged over time.
Speciation
The process by which one ancestral species splits into two or more distinct species.
The scientific method is a flexible, iterative process for investigating natural phenomena. It does not follow a rigid sequence; scientists regularly loop back, revise hypotheses, and repeat experiments when new evidence appears.
Formulate a hypothesis that is testable and falsifiable
Design an experiment with clearly defined independent and dependent variables
Include a control group that provides a baseline for comparison
Collect and analyse data, then draw conclusions
Revise and repeat as needed when results are unexpected
Key components of any experiment include the researchers, the participants (where applicable), and the variables. The entire process contributes to a growing body of scientific knowledge.
Binomial nomenclature gives every species a two-part Latin name: genus (capitalised) + specific epithet (lowercase)
Names are italicised in print, underlined when handwritten
The genus can be abbreviated after its first mention (e.g., Homo sapiens becomes H. sapiens)
"sp" (one unspecified species) or "spp" (several) can replace the specific epithet
Taxonomic classification groups organisms by shared characteristics and evolutionary relationships
Tools for exploring classification include dichotomous keys (paired yes/no questions) and phylogenetic trees (branching diagrams of lineage)
Classifications are dynamic: they shift as new discoveries and DNA evidence emerge
Charles Darwin proposed five foundational ideas:
Perpetual change – the universe and life are in constant flux
Gradualism – small changes accumulate over time into large evolutionary shifts
Natural selection – organisms with advantageous traits survive and reproduce at higher rates
Common descent – all living organisms trace back to a shared ancestor
Multiplication of species – one ancestral species can split into multiple distinct species (speciation)
Supporting evidence for evolution:
Fossil records showing gradual change over geological time
Intermediate (transitional) species bridging gaps between groups
Homologous structures: similar anatomy in different species pointing to common ancestry
Direct observations of speciation, particularly in isolated populations such as island species
Darwin's four postulates of natural selection:
Variation – individuals in a population differ in their traits
Inheritance – traits are passed from parents to offspring
Differential survival and reproduction – some traits confer advantages, leading to greater reproductive success
Overproduction – more offspring are born than can survive, creating competition
Adaptation refers to traits that enhance survival and reproduction. Fitness, in biology, is measured by an organism's reproductive output relative to others in the population. Natural selection drives evolution by reducing the frequency of less advantageous traits and increasing the prevalence of beneficial ones, changing the population's genetic makeup over generations.
Students often confuse a hypothesis with a theory. A hypothesis is a single testable prediction; a theory is a broad, well-supported explanation backed by extensive evidence. A theory does not "graduate" from a hypothesis, it is a different category altogether.
"Survival of the fittest" does not mean the strongest or fastest organism wins. Fitness in biology refers solely to reproductive success: the organism that leaves the most viable offspring is the fittest.
Natural selection does not act on individuals. Individuals do not evolve during their lifetimes. Populations evolve over generations as allele frequencies shift.
Taxonomic classifications are not permanent. Students sometimes treat the Linnaean hierarchy as fixed, but classifications are revised regularly as new molecular and fossil evidence emerges.
⚠️ Know the difference between a hypothesis and a scientific theory. This distinction appears on nearly every introductory biology exam.
⚠️ Be able to identify the independent variable, dependent variable, and control group in a described experiment.
⚠️ Understand how to write and format a binomial name correctly (italics, capitalisation, abbreviation rules).
⚠️ Be able to list Darwin's four postulates of natural selection in order and explain each one.
⚠️ Distinguish between homologous structures (shared ancestry) and analogous structures (similar function, different origin). Exams frequently test whether students can tell them apart.
True or False: A scientific theory is just a hypothesis that has not yet been proven. Answer: False. A theory is a well-substantiated, broadly explanatory framework supported by extensive evidence.
Fill in the blank: In binomial nomenclature, the first part of the name is the ______ and the second part is the ______. Answer: genus; specific epithet.
True or False: Natural selection acts on individual organisms, causing them to evolve within their own lifetimes. Answer: False. Natural selection acts on populations over generations.
Fill in the blank: Darwin's four postulates are variation, inheritance, differential survival and reproduction, and ______. Answer: overproduction.
True or False: Taxonomic classifications never change once established. Answer: False. They are revised as new evidence emerges.
Q: A researcher wants to test whether fertiliser concentration affects plant height. Identify the independent variable, dependent variable, and what the control group should be.
A: The independent variable is fertiliser concentration (the factor being manipulated). The dependent variable is plant height (the outcome being measured). The control group consists of plants grown with no fertiliser, providing a baseline for comparison.
Q: Explain the difference between a hypothesis and a scientific theory, and give one example of each.
A: A hypothesis is a specific, testable prediction (e.g., "Plants grown in sunlight will grow taller than plants grown in shade"). A scientific theory is a broad, well-supported explanation of natural phenomena (e.g., the theory of evolution by natural selection). A theory is not simply a promoted hypothesis; it is a different level of explanation supported by converging lines of evidence.
Q: Write the scientific name of the domestic dog correctly. What rules must you follow?
A: Canis lupus familiaris. The genus (Canis) is capitalised, the specific epithet (lupus) and subspecies (familiaris) are lowercase, and the whole name is italicised (or underlined if handwritten).
Q: List Darwin's four postulates of natural selection and briefly explain how they lead to evolutionary change.
A: (1) Variation: individuals differ in traits. (2) Inheritance: traits are heritable. (3) Differential survival and reproduction: some trait variants confer advantages. (4) Overproduction: more offspring are produced than can survive, creating competition. Together, these mean that advantageous traits become more common in each generation, shifting the population's genetic composition over time.
Q: What is homology, and why is it considered evidence for evolution?
A: Homology refers to structural similarities in different species that arise from a shared common ancestor (e.g., the forelimb bones of humans, bats, and whales). These similarities suggest the species diverged from a common ancestor rather than evolving independently, supporting the theory of common descent.
This material connects directly to genetics and cell division: natural selection only works because traits are heritable, which requires DNA replication, mitosis, and meiosis. Understanding classification is essential for every later unit on biodiversity, from prokaryotes through to animals, because the naming and grouping system introduced here is used throughout the course. Evolutionary theory also underpins the study of adaptation in plants (seed dispersal strategies) and animals (feeding and sensory adaptations).
Scientific method, hypothesis vs theory, independent variable, dependent variable, control group, experimental design, binomial nomenclature, Linnaeus, taxonomy, genus, specific epithet, dichotomous key, phylogenetic tree, cladogram, Darwin, Darwinism, natural selection, survival of the fittest, adaptation, fitness, gradualism, common descent, speciation, fossil record, homology, homologous structures, transitional species, BIO 101, biology principles and diversity