Outline the types of evidence that can be used to support the theory of evolution.

Explain two examples of evolution in response to an environmental change.

Remember, up to TWO “quality of construction” marks per essay.

a. fossils (give evidence of evolution);
b. fossils show different species existed in the past/species changed over time;
c. selective breeding of (domesticated) animals/crop plants;
d. selective breeding shows that (artificial) selection can cause rapid change;
e. homologous (anatomical) structures/vestigial organs (give evidence of evolution);
f. homologous structures/pentadactyl limbs/other example show common ancestry;
g. DNA/base/amino acid sequences show (common) ancestry/species diverged;

Do not award marks for examples of evolution in response to environmental change such as melanism as this is tested in part (c) of this question.

Remember, up to TWO “quality of construction” marks per essay.

For each example:
a. a named example of a species that has evolved in this way;
b. description/clear statement of the change that occurred in the environment;
c. description/clear statement of different varieties (that existed at the same time);
d. explanation of/reason for one variant having a selective advantage;
e. the change in the population/species due to natural selection/evolution;
Do not award the last mark if the change is explained using Lamarckism rather than natural selection.

Example:
f. Staphylococcus aureus/MRSA/Clostridium difficile/other named species;
g. introduction/use of an antibiotic/named antibiotic;
h. some bacteria were resistant and others were not;
i. resistant bacteria survived (and multiplied) while non-resistant were killed;
j. percentage of the population showing resistance increased;

[8] can be awarded if the candidate scores [5] for one example and [3] for the other.
Do not accept examples where the evidence of evolution comes from fossils, or where the variation is not heritable.

There were some good accounts of the types of evidence for evolution. Nearly all mentioned fossils and many also included homologous structures. One fault in some answers was to include examples where natural selection can be used to explain phenomenon but which in themselves do not provide convincing evidence for evolution because there are other possible explanations.

Answers to this part of the question were also poor in many cases. Science must be based on evidence that is as strong as possible. This is especially true with evolution, where many non-scientists remain to be convinced. Much of the evidence presented by candidates here would convince no-one, with inaccurate and in some cases invented examples. Only cases based on known environmental change were accepted, so for example supposed increases in the height of trees and a consequent lengthening of the necks of giraffes was not accepted, nor hypotheses about human evolution. There were many very vague accounts of Galapagos finches which did not include any reference to environmental change. El Niño and La Niña cause environmental change in the Galapagos archipelago and evolution in response is well researched but this evidence was rarely included in answers. The case of the peppered moth was often cited and some answers described it well. The other case that was successfully described was the development of antibiotic resistance in bacteria.