Evolution and speciation

Question 1

Evolution as change in the heritable characteristics of a population

Answer 1

This definition helps to distinguish Darwinian evolution from Lamarckism. Acquired changes that are not
genetic in origin are not regarded as evolution.
NOS: The theory of evolution by natural selection predicts and explains a broad range of observations and
is unlikely ever to be falsified. However, the nature of science makes it impossible to formally prove that it
is true by correspondence. It is a pragmatic truth and is therefore referred to as a theory, despite all the
supporting evidence.

Question 2

Evidence for evolution from base sequences in DNA or RNA and amino acid sequences in proteins

Answer 2

Sequence data gives powerful evidence of common ancestry.

Question 3

Evidence for evolution from selective breeding of domesticated animals and crop plants

Answer 3

Variation between different domesticated animal breeds and varieties of crop plant, and between them
and the original wild species, shows how rapidly evolutionary changes can occur.

Question 4

Evidence for evolution from homologous structures

Answer 4

Include the example of pentadactyl limbs.

Question 5

Convergent evolution as the origin of analogous structures

Answer 5

Students should understand that analogous structures have the same function but different evolutionary
origins. Students should know at least one example of analogous features.

Question 6

Speciation by splitting of pre-existing species

Answer 6

Students should appreciate that this is the only way in which new species have appeared. Students should
also understand that speciation increases the total number of species on Earth, and extinction decreases it.
Students should also understand that gradual evolutionary change in a species is not speciation.

Question 7

Roles of reproductive isolation and differential selection in speciation

Answer 7

Include geographical isolation as a means of achieving reproductive isolation. Use the separation of
bonobos and common chimpanzees by the Congo River as a specific example of divergence due to
differential selection.

Question 8

Differences and similarities between sympatric and allopatric speciation

Answer 8

Students should understand that reproductive isolation can be geographic, behavioural or temporal.

Question 9

Adaptive radiation as a source of biodiversity

Answer 9

Adaptive radiation allows closely related species to coexist without competing, thereby increasing
biodiversity in ecosystems where there are vacant niches.

Question 10

Barriers to hybridization and sterility of interspecific hybrids as mechanisms for of preventing the
mixing of alleles between species

Answer 10

Courtship behaviour often prevents hybridization in animal species. A mule is an example of a sterile
hybrid.

Question 11

Abrupt speciation in plants by hybridization and polyploidy

Answer 11

Use knotweed or smartweed (genus Persicaria) as an example because it contains many species that have
been formed by these processes.
Note: When students are referring to organisms in an examination, either the common name or the scientific
name is acceptable.