Covers anatomical, embryological, biogeographical and molecular evidence, and phylogenetic trees.
Lesson Summaries
Homologous structures share a common origin but may differ in function and are evidence of divergent evolution; analogous structures share function but not origin and result from convergent evolution; vestigial structures are reduced remnants of once-useful features. Structures must be compared by origin, not appearance.
Similar early embryonic features across vertebrates suggest shared ancestry and conserved developmental genes. Embryology supports common ancestry most strongly when combined with other evidence; it does not mean that embryos pass through the adult stages of their ancestors.
The geographic distribution of species reflects evolutionary history. Wallace's Line, island endemism and continental isolation are explained by common ancestry, divergence, dispersal and plate tectonics rather than by present-day environment alone.
Comparing DNA and protein sequences shows that more similar sequences indicate more recent common ancestry. Molecular clocks estimate divergence times, and molecular data can correct misleading morphology produced by convergent evolution.
Phylogenetic trees and cladograms represent evolutionary relationships from shared derived characteristics. Nodes are common ancestors, tips are taxa, and the most recent common ancestor defines how closely two groups are related. Parsimony prefers the tree requiring the fewest evolutionary changes.
1. Analogous structures are similar in...
2. Comparative embryology studies evolution by comparing...
3. Biogeography is the study of...
4. Molecular evidence for evolution compares...
5. In cladistics, a clade is:
6. A derived characteristic (synapomorphy) is best described as:
7. Distinguish between homologous and analogous structures, and explain what each tells us about evolutionary relationships. 4 MARKS
1 mark: homologous share a common origin | 1 mark: analogous share function but not origin | 1 mark: homologous indicate common ancestry (divergent evolution) | 1 mark: analogous result from convergent evolution and can mislead classification
8. Explain how molecular evidence can support or correct conclusions drawn from anatomical evidence. 4 MARKS
1 mark: molecular evidence compares DNA or protein sequences | 1 mark: more similar sequences indicate more recent common ancestry | 1 mark: it can confirm relationships suggested by anatomy | 1 mark: it can correct misleading morphology from convergent evolution
7. Homologous structures share the same basic origin and underlying structure even if their functions differ, such as the pentadactyl limb of mammals; they indicate descent from a common ancestor (divergent evolution). Analogous structures perform a similar function but have different origins, such as the wings of insects and birds; they result from convergent evolution under similar selection pressures. Homologous structures therefore reveal evolutionary relatedness, while analogous structures can mislead classification if appearance alone is used.
8. Molecular evidence compares DNA or protein sequences between species, where greater similarity indicates more recent common ancestry. When molecular data agree with anatomical comparisons they strengthen a conclusion about relatedness. When anatomy is misleading, for example where convergent evolution has produced similar-looking but unrelated structures, molecular evidence can correct the classification by showing the true pattern of ancestry. Molecular and anatomical evidence are strongest when used together.