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Summary document of Chapter 5 Evolution and biodiversity IB Biology
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Evolution5.1 Evidence for evolution
Essential idea:
Evolution is defined as the cumulative changes
There is overwhelming evidence for the
in heritable characteristics of a population
evolution of life on Earth.
over time.
Living organisms control their composition
Cumulative change: small changes upon small changes over many generations.
by a complex web of chemical reactions
Heritable characteristics: gene-controlled factors
Population: not an individual
It is distinct from the acquired characteristics that an organism may develop during its lifetime.
Evolutionary changes are present in the population’s gene pool as changes in the allele
frequency, not just one individual organism’s genes. The basis for evolution is genetics and
how the environment interacts with those heritable characteristics.
Þ Natural selection: drives evolution, but natural selection ≠ evolution
o This process explains how a species survives as a consequence of its ability
to adapt, which depends on its genetic variability and whether that genetic
variability is an advantage to the species. These adaptations may be either
physical or behavioral.
o The factors that can contribute to changing environments include climate
change, natural disasters, immigration of a new predator or prey into or
emigration of a predator or prey out of the environment, or the arrival of a
competitor for the same food source.
o Organisms that survive hostile or changing circumstances normally live to
reproductive age and pass on their genes to their progeny.
Dinosaurs are closer to
A theory is a collection of facts which help scientists predict natural birds than reptiles.
occurrences. Despite the extensive evidence, there are many people Þ Archeopteryx:
who debate the theory of evolution, arguing that it is “only a theory”. transition btwn
reptiles and birds
But a theory is different from a hypothesis. A hypothesis is not
proved, while a theory is tested and corroborated unquestionably. Therefore, a theory is the
highest degree of certainty in science.
, Þ Charles Darwin developed the hypothesis of evolution, and nowadays, as it has been
proven, it is a theory.
Þ The scientific method is based on a system of making hypothesis and testing them
through rigorous collection of empirical evidence (that can be measured and recorded),
peer-review of data, statistical analysis, replication, and finally acceptance.
Exam tip
Proof for evolution:
• Fossil record You should be able to analyze evolution trees to
determine whether a characteristic is homologous
• Vestigial structures (appendix)
or not.
• Homologous structures (arms + wings) • Analogous: common characteristics that
• Selective breeding didn't appear on a common ancestor
Birds and bats have analogous
Comparative DNA
o
•
characteristics bc even though
• Observable changes they share a common ancestor, it
was not able to fly.
• Convergent evolution (usually bc their habitat
is similar) ≠ divergent evolution (homologies)
Micro vs macroevolution
• Microevolution: occurs on a small scale within a species. F. ex.: different dog races.
o Selective breeding
o Industrial melanism
o Gradual divergence
• Macroevolution: evolution that occurs in a large scale within a species, in which speciation
occurs.
o Fossil record (f. ex.: starfish)
o Comparative anatomy
o Speciation
The fossil record
If evolution has taken place, we would expect to see these changes in an organism's
characteristics if they are structural. The fossil record provides a record of the order of
physical changes in certain species over time, but may also provide evidence of behavioral
changes.
, Þ Fossils that show structural changes can be molds, imprints, casts, preserved
organisms, or parts of organisms (direct evidence, body fossils).
Þ Other fossils, like footprints, feces, or burrows, may give an indication of the
behavioral changes of an organism (indirect evidence, trace
fossils).
Þ Fossils typically form in sedimentary rock, such as limestone
and shale.
Þ Sedimentary rock forms layers or strata. Dead organisms
can be trapped in these layers and, while the soft tissues
decompose, the harder organic materials such as bone or
shells can form different types of fossils.
o The deeper they are, the older they are
Þ Because of the similarities between the fossils and nowadays
species, we can relate them to their ancestors.
o Some fossils, such as the archaeopteryx lithographica,
represent transition species
o You can reconstruct the “timeline” of species with fossils of species that no
longer exist
o In most cases no fossils can be found of organisms that do live today
o This suggests that ancestral species evolved into modern species
Fossil record: all the fossils and their relative placement in the
Heritable characteristics are the
rocks. There is technology nowadays to date the age of the
characteristics that an
rocks/fossils. This technique was known as radioisotope
organism possesses due to its
dating. Only some organisms are preserved and only the hard
genetic make-up. These
parts, which often deteriorate, so there are gaps in the fossil
characteristics can be inherited
record. However, we have records of very important links by the organism’s offspring.
that show evolutionary transitions.
These fossils are called transitional fossils and display common characteristics between
ancestral groups showing evidence for macroevolution, like the Archaeopteryx found in 1860,
that shows the transition of birds from prehistoric reptiles.
Thus, the fossil record provides evidence for evolution and
the succession of the complexity of traits. For example, the
fossil record shows that prokaryotic cells precede
eukaryotic cells and that invertebrate animals precede
vertebrates.
, Selective breeding
Selective breeding (also called artificial selection) is the process through which humans breed
animals and plants for particular traits.
Exam tip
Þ F. ex.: bc our ancestors started breeding wolves for
the better speed traits, nowadays we have galgos You are expected to understand
how selective breeding of
(wolves and dogs are the same species: Canis lupus,
domesticated animals shows how
but domestic dogs are Canis lupus familiaris). artificial selection can cause
Þ Cows are bred for milk yield or meat evolution.
Þ Crops have been bred for greater yield and/or disease
resistance.
In contrast to natural selection, this form is artificial: Natural selection: occurs when certain
humans select the animal or plant with the best traits are selected because they help the
species to reach reproductive age and
characteristics and try, through genetic crosses, to
pass on their genes.
create a breed or plant line that retains these desired
Selective breeding: A form of artificial
characteristics. The difference between the two is selection in which organisms with
that natural selection occurs in nature, but selective certain characteristics are chosen by
breeding only occurs when humans intervene. humans because they are of some
The differences between the 'wild' ancestor and the benefit. These organisms are bred to
present-day organism can be enormous. The process produce offspring that have the same
genes and, therefore, the same
to domestic breeding is the following:
characteristics.
1. Populations show variation in traits:
a. Individuals who do not show the desired traits are not allowed to breed
b. Individuals which show the most desirable traits are chosen to breed together.
i. The next generation will have an increased frequency of the desired trait.
ii. The process is repeated for many generations until the entire population
shows the desired trait
A breed is a group of animals
within a species that have specific
In the case of dogs, to put an example, it shows the artificial
and similar characteristics.
selection because most, if not all, breeds of household dogs
that exist today are the products of selective breeding. The original bloodline is from wolf-like
animals. The process probably was:
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