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Contents:
Topic 5.1 - Evidence for evolution
Topic 5.2 - Natural selection
Topic 5.3 - Classification of biodiversity
Topic 5.4 - Cladistics
Darwin and Wallace
➢ In 1831 Darwin came up with the theory of natural selection at the age of 22
○ One of the most important, controversial and misinterpreted idea in biology
➢ In 1858 Wallace independently developed a nearly identical theory
What is evolution?
➢ Evolution is defined as the process of cumulative changes in the heritage
characteristics of a population
○ Cumulative = one change isn’t enough to have a major impact on the species
➢ Speciation is the process of an evolving population changing significantly enough
so that the production of offspring with the original population becomes
impossible
○ The rise of a new species
➢ DNA changes over time due to random mutations
○ Mutations can be both positive and negative
➢ Natural selection states that the organism best adapted to its environment will
survive (= survival of the fittest)
➢ 3 of the evidence:
○ Fossil records
○ Homologous structures
○ Selective breeding
Fossil records
➢ Fossils are the petrified remains or traces of animals and plants
➢ Fossil record is the accumulation of evidence from these remains and traces
➢ The organisms living on Earth are constantly changing
➢ Life on Earth 500 million years ago was very different
➢ The age of a rock can be determined by carefully examining differences in the ratios
of isotopes
➢ If a fossil of a bone/shell has a higher level of carbon-14, it’s younger than one with
a low level of carbon-14
○ Carbon-14 is radioactive, but it loses its radioactivity as it decays becoming
more stable
➢ Other isotopes with longer half-lives, such as potassium-40, can be used as well
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, Evidence for evolution Topic 5.1 Biology SL
Artificial selection
➢ The science of breeding domesticated animals provides a good record of recent
changes in the heritage characteristics
➢ Artificial selection is when the farmers and breeders choose which animals will
reproduce and which will not
○ It’s not the driving force of evolution in natural ecosystems
➢ The breeders choos animals with specific characteristics
Homologous structures
➢ Homologous structures are similar anatomical structures that have been found in
seemingly dissimilar species
○ Ex: pentadactyl limbs
➢ Similar bone structures with different function in modern animals point at a
common ancestor
○ May be of a different size and morphology, but the basic shape and position
are the same
Adaptive radiation
➢ Adaptive radiation occurs when 2 or more populations of a species diverge and
evolve relatively rapidly forming a small number of species
○ Happens as variations within a population allow certain members to exploit
a slightly different niche
○ A niche is a position or role within a community of an ecosystem
➢ Can happen by natural selection and the presence of a barrier
➢ Madagascar has many different regions and due to this many species of lemurs are
adapted to different niches
○ Ground, trees, rainforest, desert, diurnal, nocturnal
○ They all share a common ancestor
○ Fun fact! Lemurs are only found in Madagascar, but fossils have been found
elsewhere too. They’re not successful in competing with apes and monkeys.
When the latter become more common in fossil records, the former
becomes rarer
Gradual divergence
➢ Within a species that has a wide geographical distribution, there can be measurable
differences in DNA
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