Georgia Milestones Biology EOC, Theory of Evolution (SB6): a complete overview of how evolutionary theory developed, the evidence for evolution, natural selection, the mechanisms of change, and speciation and resistance

What the Theory of Evolution domain demands

The Theory of Evolution (SB6) is the GSE Biology domain that explains how the diversity of life arose and is supported by evidence. It is about 17 percent of the Georgia Milestones Biology EOC, the fourth-largest domain, and it ties the whole course together: cells, genetics, and classification all feed into the story of how populations change over time. Many items are reasoning and data interpretation, such as reading a table of DNA differences, interpreting a scenario of selection, or modeling how a population changes.

This guide ties together the matching topic pages, each with its own practice questions: the development of evolutionary theory, the evidence for evolution, natural selection, the mechanisms of evolution, and speciation and resistance.

How the theory developed (SB6.a)

Evolution is descent with modification: present-day species descend from earlier, different species. Charles Darwin explained the mechanism as natural selection. His thinking needed a new view of Earth's history, that the planet is very old and has changed gradually, giving evolution enough time to work. An earlier idea by Lamarck, the inheritance of acquired characteristics, was wrong because only heritable traits are inherited. Darwin did not know about genes; the later science of genetics supplied the missing source of variation (mutation) and the mechanism of inheritance (alleles), turning natural selection into the gene-based modern theory.

The evidence for evolution (SB6.c)

Several independent lines support common descent. The fossil record shows life has changed over time and preserves transitional forms. Homologous structures share the same underlying anatomy from a shared ancestor (the same forelimb bones in a human, whale, and bat) even when functions differ; analogous structures share only a function and are not evidence of ancestry; vestigial structures are reduced remnants of ancestral features. Embryology shows related species look alike as early embryos. The strongest modern line is molecular: the more similar two species' DNA or proteins, the more recently they shared a common ancestor. The case is strong because many lines agree.

Natural selection (SB6.d)

Natural selection needs four conditions: variation, overproduction and competition, differential survival and reproduction (fitness), and inheritance. Fitness means reproductive success, not strength. Selection produces adaptation, a heritable trait that improves survival and reproduction in the environment. It can be tracked as a rise in the frequency of a favorable allele over generations. The key idea is that populations evolve, individuals do not, and selection acts only on variation that already exists.

The mechanisms of evolution (SB6.d)

Evolution is a change in allele frequencies, and several mechanisms drive it. Mutation is the only source of new alleles. Natural selection is the non-random mechanism that produces adaptation. Genetic drift is random change in small populations, including the bottleneck effect (a random die-off) and the founder effect (a small group starting a new population). Gene flow moves alleles between populations through migration or gametes. The Hardy-Weinberg idea describes a non-evolving baseline ($p + q = 1$ unchanging) for comparison; a real population evolves when a mechanism disturbs it.

Speciation and resistance (SB6.b, SB6.e)

Speciation is the formation of a new species, often beginning with reproductive isolation from a geographic barrier. Isolated groups accumulate different changes; if they can no longer interbreed, they are separate species. Repeated speciation builds biodiversity, all related by common ancestry. Resistance (antibiotic or pesticide) is fast natural selection: a population varies, the drug or pesticide kills the susceptible individuals, and resistant survivors reproduce, so the resistant allele's frequency rises. The drug does not create resistance; it selects for variants that already exist.

Check your knowledge

A mix of recall and reasoning questions covering the Theory of Evolution domain. Attempt them under timed conditions, then check against the solutions.

1. Name Darwin's mechanism for how species change over time. (1 mark)
2. State why Lamarck's idea of inheritance of acquired characteristics is incorrect. (1 mark)
3. List the four conditions required for natural selection. (2 marks)
4. Define fitness as biologists use the term. (1 mark)
5. Explain the difference between homologous and analogous structures. (2 marks)
6. A table shows species P, Q, R have 3, 22, and 48 DNA differences from a human gene. Which is most closely related, and why? (2 marks)
7. Name the mechanism that is the only source of new alleles. (1 mark)
8. Classify a random die-off that changes allele frequencies in a small population. (1 mark)
9. State what reproductive isolation must lead to for two groups to be separate species. (1 mark)
10. Explain how an antibiotic causes a bacterial population to become resistant. (2 marks)