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BIOLOGY 1M03 Lecture Notes - Phylogenetic Tree, Geologic Time Scale, Radiocarbon Dating

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Jon Stone

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In the name of Allah the Gracious the Merciful
Chapter 24 Evolution by Natural Selection
Key Concepts
1) Populations and species evolve, which means that over time their heritable traits
(height, weight, abilities) change over time. Evolution is changes in allele frequencies
over time
2) Natural selection occurs when individuals with certain heritable traits produce the
most surviving offspring in a population
3) Evolution is NOT PROGRESSIVE, and doesn’t change characteristics of individuals,
but rather only changes the characteristics of the population
24.1 The evolution of evolutionary thought
Typological thinking – based on the idea that species are unchanging and variations in the
species are irrelevant (old philosophers believed in this)
Lamarack – first to propose a formal theory of evolution
He believed that organisms are created from spontaneous generation at the base of the
chain, and then evolve and move up the chain over time, and that species change because
of the inheritance of acquired characters.
- progressive theory of evolution contrary to darwins
Darwin’s claim was that the variance among species in a population was the key for
evolution because certain individuals with certain traits will produce more surviving
24.2 The Pattern of Evolution: Have Species Changed through Time?
Descent with modification” – used by Darwin to describe evolution
Means that the species existing today all descent from preexisting ancestors, but certain
traits have been modified through time
Pattern component makes 2 claims
1) Species change through time 2) Related by common ancestry
Many of Darwin’s points make use of the fossil records
A fossil is any trace, or anything left behind (bones, branches, shells tracks) of an
organism that lived in the past.
Fossils were organized to their relative age because most were found in sedimentary
rocks that form in layers, meaning that fossils in lower layers of rock were older than
fossils found in higher layers. Fossils were relatively ordered in this fashion.
Geologic time scale was also named, in relation to these fossils
Eventually radioactivity or carbon dating was used to identify the age of fossils.
Evidence for change though time (Refutes Immutable aspect of creation theory)
1) Extinction
Early 19th century, researches found many fossils that were alien to any known
species existent. They concluded that these species must exist in unknown parts of the
However, more and more fossils were being found, making this argument less
Darwin concluded that these species have gone extinct, which proves that species are
not static (unchanging), and if they have gone extinct (and they continuously have
during the course of history) than all the species living on earth today have been
2) Transitional Forms
Before Darwin published his theory researches found similarities between living
species and the fossil records of extinct species in the same geographical area.
“Law of succession” – pattern of finding living species that are similar to extinct
species that lived in the same geographical area from fossil records
Darwin said it supported his theory as it was evidence that species change over time,
and that it showed the ancestor and descent relationship between living species and
fossil records
Transitional Form – fossil species with traits that intermediate with older and
younger species
E.g. pg 509 about whales
3) Vestigial Trait (examples on pg 510)
- a reduced or completely useless structure that serves no purpose in the overall
function, but is SIMILAR to functioning organs or structures found in closely
related species
- inconsistent with the creation theory, which maintains that living things are
perfect, and therefore static
- Provides evidence to Darwins theory, showing that characteristics of species have
changed over time
Evidence that species are related (refutes relation aspect of creation theory)
1) Geographical relationships
Darwin took a 5 year trip to South America, more specifically the Galapagos Islands. He
took many bird and animals back to England.
One of the birds, Galapagos mocking bird, was presented to his naturalist friend in
England, who told him that the various Galapagos mocking birds he brought back from
neighboring islands were distinct species.
Globally, you can find similar species of animals on neighboring islands.
Darwin concluded that the mocking birds colonized neighboring Islands, and later
branched off into different species, rendering them to be placed on a phylogenetic tree.
1) Homology