Scientists investigate two sources of evidence.
Investigation 1
Fossil jaws from the same group of extinct reptiles are found in three sedimentary rock layers in an undisturbed cliff.
| Rock layer | Position in cliff | Mean width of teeth in the fossil jaw (mm) |
|---|---|---|
| A | top | 3.0 |
| B | middle | 4.6 |
| C | bottom | 6.2 |
Investigation 2
Researchers take a sample from a bacterial population. They then keep the population in the presence of an antibiotic for 60 generations before taking another sample. A bacterium is classed as resistant if it can survive and reproduce in the presence of the antibiotic.
| Sample | Total number of bacteria tested | Number of resistant bacteria |
|---|---|---|
| before exposure to the antibiotic | 125 | 5 |
| after 60 generations | 80 | 56 |
Explain how the evidence from both investigations supports the conclusion that evolution has occurred.
122 exam-style questions on OCR GCSE Biology 5.2 Natural selection and evolution, covering 5.2.1 Genetic variation within a population, 5.2.2 Developments in classification systems, 5.2.3 How evolution occurs through natural selection, 5.2.4 Evolution as change over time, 5.2.5 Evidence for evolution, and 5.2.6 Darwin and Wallace. Each one has a worked solution and a mark scheme showing where the marks go.