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Summary of IB Biology Topic 5 (Evolution & Biodiversity)
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Topic 5 - EvolutionTopic 5.1 - Evidence for Evolution
5.1.1 - Evolution
Concise de nition: change in allele frequency of a population’s gene pool over successive
generations.
5.1.2 - Fossil Record
Fossil record: all discovered and undiscovered fossils (preserved remains/traces of any organism
from remote past)
• Remains (e.g. skeleton) = direct evidence
• Traces (e.g. footprints) = indirect evidence
Fossil dating: determining age of fossils
Can be done through determining age of strata (rock layer) in which fossil is found.
• Stratum develop in chronological order
• Each strata represents a variable length of time
Law of Fossil Succession
Transitional fossils: intermediary forms within an evolutionary pathway
Fossilisation is rare —> fossil record is incomplete
Transitional fossils are used to establish links between two species suspected to be
related, (e.g. Archaeopteryx (dinosaur-bird)).
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, 5.1.3 - Selective Breeding
Selective breeding: a form of arti cial selection, whereby man intervenes in breeding of species
to produce desired traits In o spring.
Examples:
• Brassica —> broccoli, cabbage and kale
• Wild horses —> race horses and draft horses
• Aurochs —> cows —> belgian blue
• Wolves —> dogs —> hunting dogs, herding dogs, racing dogs and toy dogs
5.1.4 - Comparative Anatomy
Shared structural features may indicate common ancestry.
Homologous structures: anatomical structures that are similar in basic structure but may serve
di erent functions.
• The more similar, the more closely related the species are likely to be.
• Demonstrated adaptive radiation (species diversify from ancestor to adapt to their di erent
surroundings).
Example: pentadactyl limb
5.1.5 - Speciation
Speciation: the formation of new and distinct species via evolution.
When two populations of a species become geographically separated, they gradually diverge
from each other as they adapt to their di erent environments to become two di erent species.
Populations located in close proximity to each other/separated recently experience less
variation from one another.
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