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Chapter 4

ANT203H5 Chapter Notes - Chapter 4: Chronospecies, Darwin'S Finches, Stratum

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Esteban Parra

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Notes From Reading
-When so-called creation scientists dispute evolution, they generally mean macroevolution
-Creationism argues that we cannot directly observe changes over millions of years and
therefore cannot conduct scientific tests
-We rely on some record – geologic strata or stellar configurations
-Geology makes use of the fact that geologic processes occur in a regular manner and so
occurred in the same way in ancient times
oAvailable information about current geologic processes helps explain patterns of
change in the past
-Evolutionary science takes what we know about microevolution and extends it to explain
the long-term pattern of macroevolution
The Birth and Death of Species
-The origin of new species has been observed in historical times and in the present
-Charles Darwin sought to explain the basic nature of evolutionary change, believing that
extension of these principles could explain the formation of new species
What Is a Species?
-Biological Species ConceptA definition of species that focuses on reproductive
capabilities, whereby organisms from different populations are considered to be in the
same species if they naturally interbreed and produce fertile offspring
oNote: organisms from different populations must be capable of interbreeding.
These matings must occur in nature and take place naturally (ie. tiger and lions
mate in zoos but don’t breed together in nature). The offspring must be fertile,
capable of producing further offspring.
-Example: Mules are farm animals produced as the offspring of a horse bred with a
oThey interbreed naturally (satisfying the first and second part of the definition)
oMules are sterile and cannot produce further offspring
oSince not fertile, the horse and he donkey are considered separate species
-The biological species concept assumes that two organisms either belong or do not
belong to the same species (no intermediate state)
-Problem: if some populations of species A evolved into species B, at what point did
those populations stop being species A and start being species B?
oSpecies concept suggests that this change was instantaneous, because a creature
belongs to either one species or the other
oIn real world, the evolution and variation work to break down rigid systems of
Species Change
-A single species can change over time such that enough differences accumulate that we
would choose to give it a different species name
oAnagenesis – the transformation of a single species over time
-Chronospecies – Labels given to different points in the evolutionary lineage of a single
species over time. As a species changes over time, the different stages are labeled as
chronospecies in recognition of the biological changes that have taken place
oIn evolution, chronospecies are different stages in the evolution of a single
evolutionary lneage
-Cladogenesis – The formation of one or more new species from another over time
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Notes From Reading
-The problem of species naming is complicated by the fact that evolutionary relationships
among fossil forms are not always clear
-For a species to become a new species, these genetic differences must be great enough to
prevent successful interbreeding with the original parent species
-For this to occur, the population must become reproductively isolated from the original
parent species
Reproductive Isolation
-Reproductive IsolationThe genetic isolation of populations that may render them
incapable of producing fertile offspring
oThe genetic change that can lead to an inability to produce fertile offspring
-The first step in speciation is the elimination or reduction of gene flow between
populations (populations must be genetically isolated from one another for speciation to
oSpeciation – The origin of a new species
-Common form of isolation in animal species: geographic isolation
oTwo populations are separated by a physical barrier, (I.e., river or mountain
range, great distances)
-Populations may be isolated by behavioral differences such as feeding habits
oSome groups may eat during the day, and other during dusk
oSince groups aren’t in frequent contact with one another, there is opportunity for
isolation to develop
Genetic Divergence
-Other evolutionary forces must act upon this isolation to produce a situation in which the
isolation groups have changed sufficiently to make fertile interbreeding no longer
-Isolation does not always lead to speciation
-Mutation might act to increase variation among populations as it occurs independently in
the genetic composition of separate groups
-Genetic drift also contributes to differences in allele frequencies among small populations
-Fossil record shows that there are times when evolutionary change is slow, and times
when it is fast (in geologic terms)
Adaptive Radiation
-Adaptive Radiation – The formation of many new species following the availability of
new environments or the development of a new adaptation
-Example: Darwin finches – the availability of new environmental niches led to the rapid
speciation of finches in the Galapagos Islands
Extinctions and Mass Extinctions
-It is estimated that more than 99 percent of all species that ever existed have become
-The exact causes of a species’ death vary from situation to situation
-When the environment changes too rapidly or when the appropriate genetic variations do
not exist, a species can become extinct
-Mass Extinction – Many species becoming extinct at about the same time
oFossil records documents 5 mass extinctions in the history of our planet (some
are suggesting we are currently in a period of extinction that might be the sixth)
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