Evidence for evolution — AQA GCSE Biology
Test yourself on Evidence for evolution with AQA GCSE practice questions.
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Evidence for evolution explained
Evolution is supported by multiple independent lines of evidence.
Read the full explanation
Fossils show organisms from the past, often unlike living species, and their positions in rock layers reveal change over time. Antibiotic resistance in bacteria provides observable evidence: when bacteria reproduce rapidly, random mutations can make some individuals resistant. In the presence of an antibiotic, susceptible bacteria die while resistant bacteria survive and reproduce, so the proportion of resistant bacteria increases. This is natural selection in action. Students should describe both sources, explain what each shows and link them to the idea that species change over time.
The theory of evolution by natural selection is now widely accepted.
The theory of evolution by natural selection explains how species change over time. Individuals in a population vary because of differences in their genes. Some variants are better suited to the environment, so they are more likely to survive and reproduce. Their offspring inherit the advantageous characteristics, so these become more common in the population over many generations. The theory is widely accepted because evidence from many areas of biology supports it, including the fossil record, the similarities between organisms, and observations of rapid evolution such as antibiotic resistance in bacteria. Acceptance means the scientific community treats it as the best explanation supported by evidence.
Evidence for Darwin’s theory is now available as it has been shown that characteristics are passed on to offspring in genes.
Darwin proposed that characteristics are passed from parents to offspring, but he did not know how inheritance worked. Modern genetics provides the mechanism: genes are sections of DNA that code for characteristics, and they are passed from parents to offspring in gametes. Alleles are different versions of a gene, and the combination of alleles an offspring inherits affects its characteristics. This explains why variation exists in a population and why advantageous characteristics can become more common over generations. Understanding genes therefore supports Darwin’s theory by showing how inherited variation arises and how natural selection can change populations over time.
There is further evidence in the fossil record and the knowledge of how resistance to antibiotics evolves in bacteria.
Two strong sources of evidence support evolution. The fossil record shows organisms from the past, often different from living species, and the sequence of fossils in rock layers shows change over time. Antibiotic resistance in bacteria shows evolution happening quickly: random mutations produce some bacteria that are resistant, and when an antibiotic is used, these bacteria survive and reproduce while others die. The proportion of resistant bacteria increases, so the population evolves. Together, fossils show long-term change and antibiotic resistance shows natural selection in action, making the theory of evolution by natural selection well supported.
Your focus
- Describe how fossils provide evidence that organisms have changed over time.
- Explain how antibiotic resistance in bacteria demonstrates natural selection.
- Use evidence from fossils and antibiotic resistance to support the theory of evolution.
Show all 12 objectives
- Describe the main steps of evolution by natural selection.
- Explain why the theory of evolution is widely accepted.
- Relate evidence from fossils and antibiotic resistance to the theory of natural selection.
- Describe how genes and alleles are passed from parents to offspring.
- Explain how knowledge of inheritance supports Darwin’s theory of evolution.
- Use the idea of alleles to explain variation within a population.
- Describe how the fossil record provides evidence for evolution.
- Explain how antibiotic resistance in bacteria evolves by natural selection.
- Use both sources of evidence to support the theory of evolution.
Evidence for evolution exam tips
Marking Points
- Fossils are preserved remains or traces of organisms from the past, often found in sedimentary rock, and can show structures not seen in living species.
- The fossil record shows that organisms have changed over time, with simpler forms generally found in older rocks and more complex or different forms in newer rocks.
- Antibiotic resistance arises from random mutations in bacterial DNA that give some bacteria an advantage when an antibiotic is present.
- When an antibiotic is used, susceptible bacteria are killed while resistant bacteria survive and reproduce, increasing the proportion of resistant bacteria in the population.
- Both fossils and antibiotic resistance provide evidence that populations can change over time through natural selection, supporting the theory of evolution.
- Variation exists within populations because individuals have different alleles, produced by mutation and sexual reproduction.
- Individuals with characteristics better suited to their environment are more likely to survive and reproduce, so they pass on the advantageous alleles.
- Over many generations, the proportion of individuals with advantageous characteristics increases, and the population changes.
- The theory is widely accepted because multiple independent lines of evidence, including fossils and antibiotic resistance, support it.
- Genes are sections of DNA that carry the instructions for characteristics and are passed from parents to offspring.
- Alleles are different versions of a gene, and different combinations of alleles produce variation within a population.
- Inherited variation is the raw material on which natural selection acts, because some alleles give a survival advantage.
- Knowledge of genes supports Darwin’s theory by explaining how characteristics are inherited and how populations can change over generations.
- Fossils are preserved remains or traces of past organisms, and the fossil record shows that species have changed over time.
- Older rock layers generally contain simpler or different organisms, while newer layers contain more recent forms, showing a sequence of change.
- Antibiotic resistance evolves when random mutations produce resistant bacteria, and the antibiotic selects these bacteria by killing susceptible ones.
- Resistant bacteria survive and reproduce, so the proportion of resistant bacteria in the population increases over generations.
- Both lines of evidence support the theory of evolution by natural selection because they show populations changing over time.
Examiner Tips
- 💡Use the word ‘selection’ when explaining antibiotic resistance: state that the antibiotic selects resistant bacteria rather than causing resistance.
- 💡When describing fossils, refer to changes over time and give a clear example, such as a fossil showing a feature absent in living relatives.
- 💡Link each piece of evidence back to evolution explicitly, for example by stating that the evidence shows populations changing over many generations.
- 💡Use the phrase ‘survival of the fittest’ only if you also explain that ‘fittest’ means best suited to the environment, not strongest.
- 💡Structure an explanation as variation, selection, inheritance and change over generations.
- 💡Refer to named evidence, such as fossils or antibiotic resistance, to show why the theory is accepted.
- 💡Use the terms gene, allele, DNA and gamete accurately when explaining inheritance.
- 💡Link inheritance explicitly to natural selection by stating that advantageous alleles are passed on and become more common.
- 💡Avoid saying that an organism ‘has a gene for’ a trait in a way that ignores alleles; refer to alleles where variation is involved.
- 💡When explaining antibiotic resistance, state clearly that the antibiotic is the selection pressure.
- 💡Use the fossil record to describe change over time, and antibiotic resistance to describe natural selection in action.
- 💡Make the link to evolution explicit in your final sentence, for example by stating that the evidence supports the theory of evolution by natural selection.
Common Mistakes
- Thinking that bacteria deliberately become resistant in response to an antibiotic; the correct idea is that random mutation occurs first and the antibiotic then selects resistant bacteria.
- Believing that individual bacteria change during their lifetime; the correct idea is that the population changes because resistant individuals survive and reproduce.
- Assuming fossils only show complete bodies; the correct idea is that fossils include bones, shells, impressions and traces, and often only parts are preserved.
- Saying that individuals evolve; the correct idea is that populations evolve as allele frequencies change over generations.
- Thinking that organisms choose to change to suit their environment; the correct idea is that variation arises randomly and natural selection acts on it.
- Believing that acceptance means the theory is proven beyond all doubt; the correct idea is that it is strongly supported by a wide range of evidence.
- Confusing genes with alleles; the correct idea is that a gene is a section of DNA and alleles are different versions of that gene.
- Thinking that acquired characteristics can be inherited; the correct idea is that only genetic information passed in gametes is inherited.
- Believing that Darwin knew about genes; the correct idea is that the genetic mechanism was discovered later and now provides evidence for his theory.
- Thinking that antibiotics cause mutations; the correct idea is that mutations occur randomly and the antibiotic selects resistant bacteria.
- Believing that resistance develops in a single bacterium during treatment; the correct idea is that the population changes over generations as resistant bacteria reproduce.
- Assuming the fossil record is complete; the correct idea is that it is incomplete because many organisms do not fossilise or are not yet found.