Written for this site from the class slides, with textbook page references for each statement. The chapter is on pages 138–150 of the course textbook. Image credits are on slide 16.
Evolution is a change in the inherited characteristics of a population. Changes acquired during a lifetime are not genetic, so they are not evolution. This is what separates Darwin's theory from Lamarck's idea that acquired traits pass to offspring.
Base sequences in DNA or RNA, and amino acid sequences in proteins, can be compared. Mutations accumulate over time, so closer relatives have more similar sequences. This is powerful evidence of common ancestry.
Humans have chosen which animals and crops breed. Domesticated breeds now differ greatly from one another and from wild species. This shows how rapidly heritable characteristics can change under selection.
Homologous structures have a similar basic structure, but they may have different functions. Pentadactyl limbs are the classic example: bones follow one pattern, whether used for flying, swimming or walking.
Analogous structures have the same function, but different evolutionary origins. They arise by convergent evolution, as with the wings of birds and insects.
This is the only way in which new species have appeared. Speciation adds to the total of species alive, and extinction takes away from it.
Speciation requires both reproductive isolation, which stops gene flow, and differential selection, which makes traits diverge. A geographical barrier can isolate populations. The Congo River separates bonobos from chimpanzees, which have diverged because of different conditions on each side.
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A printable worksheet covering all seven statements, from quick recall to data questions and a longer answer. It has 36 marks and takes about 35 minutes, or you can do one section at a time.
Your teacher has the mark scheme.
Questions built on realistic experimental data, in the style of Paper 1B and Paper 2. Work them on paper and show your working. 19 marks in total. Your teacher has the mark scheme.
Two groups of closely related fern species were studied. Group A (three species) grows on rocks in temperate forests of North America; its species look almost identical but cannot interbreed. Group B (four species) grows on trees in tropical forests; its species look clearly different. The table shows the percentage difference in a DNA sequence between each pair of species in a group.
| Group | Sequence difference between pairs of species / % | |||||
|---|---|---|---|---|---|---|
| A (temperate, 3 species) | 0.8 | 1.1 | 1.3 | |||
| B (tropical, 4 species) | 3.2 | 4.5 | 5.1 | 2.8 | 3.9 | 4.4 |
Two species of ground beetle live in neighbouring valleys in the mountains of Japan. A section of mitochondrial DNA was sequenced in 25 beetles of each species. Each different sequence is called a haplotype.
Each main flight feather has a vane on each side of the central shaft. In flying birds the front vane is much narrower than the back vane, so the feather is asymmetric. Asymmetry was measured as the width of the back vane divided by the width of the front vane.
| Flying birds | Asymmetry | Flightless birds | Asymmetry |
|---|---|---|---|
| Pigeon | 2.9 | Ostrich | 1.0 |
| Golden eagle | 3.2 | Emu | 1.1 |
| Herring gull | 2.7 | Kiwi | 1.2 |
| House sparrow | 3.0 | Flightless cormorant | 1.3 |
You will need: Haemoglobin beta sequences for human and several other species from UniProt, spreadsheet
Safety: No practical hazards.
Carry this out with your teacher's supervision and follow your school's lab rules.
Evolution is supported by independent evidence from fossils, anatomy, selective breeding and molecular sequences.
In everyday speech, a theory is a guess. Consider how scientific usage differs, and why that matters for public understanding.
Summarised in our own words. Use each code to find the exact wording in your textbook or the IB subject guide.
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