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VCE Biology Unit 4 AOS 2
Introduction to Evolution
Evolution is the central, unifying theory of biology, explaining the immense diversity and underlying similarity of all life on Earth. This area of study investigates the processes that cause genetic changes in populations over time (microevolution) and the large-scale patterns that lead to the formation of new species over geological time (macroevolution).
The Gene Pool & Allele Frequencies
A population is a group of interbreeding individuals of the same species. Its gene pool is the total collection of all genes and their alleles. Evolution, at its core, is the change in allele frequencies in a population’s gene pool over successive generations. For example, if the frequency of allele ‘A’ changes from 60% to 70% in a population, evolution has occurred.
Mechanisms of Changing Allele Frequencies
Several distinct forces can alter the allele frequencies in a gene pool. Click the cards below to explore these engines of microevolution.
Select a mechanism to learn more.
Speciation: The Origin of Species
Speciation is the evolutionary process by which populations evolve to become distinct species. The key element is the evolution of reproductive isolation, which prevents gene flow. Click each mode of speciation to see how it works, with reference to the mandatory VCE case studies.
Select a mode of speciation.
The Fossil Record
Fossils are the preserved remains or traces of past life, providing the most direct evidence that life has changed over time. They reveal organisms different from those alive today and show the evolutionary changes within groups of organisms.
Dating Fossils
Relative Dating: Determines the age of a fossil by its position in rock strata. Deeper layers are older. Index fossils help correlate layers across locations.
Absolute Dating: Provides a numerical age using radiometric methods (e.g., Carbon-14, Potassium-Argon), which measure the decay of radioactive isotopes.
Transitional Fossils
These are fossils that exhibit traits of both an ancestral group and its descendant group, providing a snapshot of evolutionary change. A classic example is Archaeopteryx, which has features of both dinosaurs (teeth, long tail) and birds (feathers, wings), linking the two groups.
Structural Morphology
Comparing the physical structures of organisms provides strong evidence for evolutionary relationships and showcases patterns of divergent and convergent evolution.
Homologous Structures: The Pentadactyl Limb
Homologous structures share a common underlying anatomy due to shared ancestry, but are modified for different functions. This demonstrates divergent evolution. Hover over the diagram below to see the corresponding bones highlight across species.
Molecular Homology & Phylogenetics
Comparing DNA and protein sequences provides powerful, quantitative evidence for evolutionary relatedness. The more similar the molecules, the more recently two species shared a common ancestor. This data is used to build phylogenetic trees.
DNA & Protein Comparison
By aligning sequences, we can count the differences. For example, the Cytochrome C protein is identical in humans and chimps, but has over 40 differences when compared to yeast, reflecting our distant shared ancestry.
Phylogenetic Trees
These are branching diagrams that represent a hypothesis of the evolutionary relationships between organisms. Branch points (nodes) represent common ancestors. Species sharing a more recent common ancestor are more closely related.
Major Trends in Hominin Evolution
The hominin lineage, which includes humans and our extinct bipedal relatives, shows several key trends in structural, functional, and cultural evolution. One of the most significant is the increase in cranial capacity, or brain size.
Trend in Hominin Cranial Capacity
This chart shows the average cranial capacity of key hominin species over time, illustrating the general trend of encephalization.
Interactive Hominin Timeline
Our evolutionary history is not a straight line but a complex, “bushy” tree. Click on each hominin in the timeline below to explore its key features, the time period it lived in, and its associated cultural innovations.
Select a hominin from the timeline to view details.
