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Summary Evolution IB biology HL
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5.1 Evidence for evolutionEvolution is the cumulative change in the heritable characteristics of a population. Two
important separate processes:
1. A source of variation between individuals of one species
2. A change in the frequency of the genes in the gene pool of a population
• Fossils are the mineralized remains of organisms (process is called fossilization)
• Dead organisms usually decompose, but if they are covered by sediment after they die, they
may, totally or in part become fossils
• Fossils are usually formed in sandstone or clay which compresses the skeletons into two
dimensions. Three-toed horses -> one-toed horses (suited to the changing climate)
• Transitional fossils shows the links between groups by exhibits traits common to both the
ancestral group and its derived descendant group (e.g. archaeopteryx - evolution of birds)
Evidence for evolution: fossil record, homologous structures, selective breeding, vestigial
structures, comparative DNA, observable changes
Five-fingers rule
1. Variation. Mutation+Sexual reproduction - crossing over and/or independent assortment
2. Overproduction of offspring
3. Natural selection. ——> food, partner for breeding
4. Reproduction.
5. Allele frequency.
Evolution of homologous structures by adaptive radiation
Common ancestor——> common traits —— homologous structures ——> supports the concept of
evolution
Selective breeding of domesticated animals (the artificial selection)
Selective breeding (artificial selection) - using individuals with desired traits for breeding to
accentuate the desired traits
~ Dogs - Canis familiaris (the same species)
~ the Frisian Holstein breed has the high milk yield, increasing numbers of these cows developed
serious problems with their legs, often resulting in culling when the cows were only a few years
old. Cross breeding —-> easy calving, strong legs, without focusing exclusively on milk yield
,Melanistic moths - the case of the pepper moth and “industrial melanism”
• in the past the trees on which the moth rested were covered with off-white lichen (beneficial for
white form of species)
• Due to coal-based industry around 185-, the trees became covered with soot (beneficial for the
dark (melanic) form)
• Reduced use of coal made the trees covered un algae, so both forms of the moths are common -
balanced polymorphism
Similar example is the harlequin ladybird - highly variable in appearance - over 100 different forms
Pentadactyl forelimbs
• Comparison of the pentadactyl limb of mammals, birds, amphibians and reptiles reveal
differences that clearly related to the different methods of locomotion (the various movement
to propel themselves from one place to another)
• Human arms are similar in structure to the front paws of a dog, lizard, the wings and the flipper
of a whale
• Pentadactyl limb (five digit) common to all tetrapods. Same bones, although the relative size of
bones may differ
Species can gradually diverge into separate species
• Darwin’s finches migrated to the Galápagos Islands. These ancestral finches were most likely
ground-dwelling and ate mainly seeds
• the populations adapted to the different local environments which, after a lot of time and
genetic isolation, resulted 10 more different species
• It is possible that there is no complete genetic isolation, since different populations
occasionally breed ——> less adapted offsprings, less successful reproduction
• Geography isolation——> genetic isolation of the populations ——> new species (process
called speciation)
• Ring species - series of neighbouring populations, each of which interbreeds with closely
sited related populations
• Although neighboring populations can interbreed, the difference between the population
remain. The more remote populations will differ too much to interbreed.
~ Sea gull (Larus) living around the North Pole. Some populations live in Europe, while other
populations reach across Siberia. They can breed and hybridize. However Larus fuscus us and
Larus argentatus will not breed, eben when sharing the same area
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