What kinds of evidence support the theory of evolution?
Topic 7.6 Evidence of Evolution: describe the lines of evidence (fossil, anatomical, molecular, biogeographical) that support evolution.
A focused answer to AP Biology Topic 7.6, covering fossil, anatomical (homologous and vestigial structures), embryological, molecular and biogeographical evidence for evolution, with a worked interpretation of molecular data.
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What this topic is asking
The College Board (Topic 7.6) wants you to describe the lines of evidence that support evolution: fossil, anatomical (homologous and vestigial structures), embryological, molecular (DNA and protein sequences), and biogeographical.
Fossil and anatomical evidence
Be careful to distinguish homologous structures (similar origin, possibly different function) from analogous structures (similar function, different origin, from convergent evolution).
Molecular and other evidence
A particular strength of molecular evidence is that it provides huge numbers of independent characters (every base position is a piece of data) and can compare even very distantly related organisms, such as bacteria and humans, which share no obvious anatomy. This is why molecular data now form the backbone of phylogenetic trees.
Try this
Q1. State the difference between homologous and analogous structures. [2 points]
- Cue. Homologous structures share a common ancestral origin (similar anatomy, possibly different function); analogous structures have similar function but different evolutionary origins (convergent evolution).
Q2. Explain how molecular data indicate how closely two species are related. [2 points]
- Cue. Related species share a common ancestor and so similar sequences; differences accumulate by mutation after they diverge, so fewer differences mean a more recent common ancestor and closer relationship.
Exam-style practice questions
Practice questions written in the style of College Board exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AP 2019 (style)4 marksSection II (long FRQ excerpt, data). A table shows the number of amino acid differences in a protein between humans and four other species. (a) Explain how molecular data such as this provides evidence for evolution. (b) Predict which species is most closely related to humans, and justify your prediction using the data.Show worked answer →
A 4-point explain-and-predict FRQ on molecular evidence.
(a) Explain (2 points): (1 point) related species share a common ancestor, so their DNA and protein sequences are similar; (1 point) differences accumulate over time as mutations arise after lineages separate, so the number of differences reflects how long ago two species shared a common ancestor.
(b) Predict and justify (2 points): (1 point) the species with the fewest amino acid differences from humans is the most closely related; (1 point) because fewer differences mean less time has passed since the common ancestor, so that lineage diverged most recently.
Markers reward linking sequence similarity to common ancestry and using fewest differences to identify the closest relative.
AP 2018 (style)1 marksSection I (multiple choice). The forelimbs of humans, whales, bats and cats have the same bone arrangement but different functions. These are best described as: (A) analogous structures. (B) homologous structures. (C) vestigial structures. (D) fossils.Show worked answer →
The correct answer is (B).
Homologous structures share a common underlying anatomy because they are inherited from a common ancestor, even if they now serve different functions. Analogous structures (A) have similar functions but different origins; vestigial structures (C) are reduced remnants; fossils (D) are preserved remains.
Related dot points
- Topic 7.7 Common Ancestry: describe the structural and molecular features shared by all organisms that indicate common ancestry.
A focused answer to AP Biology Topic 7.7, covering the shared features of all life (DNA, the genetic code, ribosomes, core metabolism, membranes) that indicate common ancestry, and how conserved features reveal deep relationships, with a worked example.
- Topic 7.9 Phylogeny: interpret and construct phylogenetic trees and cladograms from shared characters and molecular data.
A focused answer to AP Biology Topic 7.9, covering phylogenetic trees and cladograms, shared derived characters, nodes and common ancestors, out-groups, and reading relatedness from a tree, with a worked tree interpretation.
- Topic 7.1 Introduction to Natural Selection: explain the conditions required for natural selection and how it leads to changes in a population.
A focused answer to AP Biology Topic 7.1, covering Darwin's reasoning, the conditions for natural selection (variation, heritability, overproduction, differential reproduction), fitness, and how selection changes allele frequencies, with a worked example.
- Topic 7.8 Continuing Evolution: explain how ongoing examples such as antibiotic resistance and pesticide resistance show that evolution continues.
A focused answer to AP Biology Topic 7.8, covering observable, ongoing evolution including antibiotic and pesticide resistance, emerging diseases, and how these illustrate natural selection in real time, with a worked example.
- Topic 7.13 Origin of Life on Earth: describe the scientific models for the origin of life, including the RNA world and the evidence supporting them.
A focused answer to AP Biology Topic 7.13, covering models for the origin of life, the formation of organic monomers, the RNA world hypothesis, protocells, the geological timeline, and the evidence behind these models, with a worked example.
Sources & how we know this
- AP Biology Course and Exam Description — College Board (2020)