BIO 156 Chapter 23 Powerpoint
Transcript of BIO 156 Chapter 23 Powerpoint
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BIO 156
Chapter 23
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HumanEvolution
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How Evolution Works
Genetic variation is the raw material of
evolution.
Changes in species occur because of
changes in genetic material. Genetic variation in a species arises from
several processes including:
Mutations
new combinations resulting from sexual
reproduction.
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Natural selection is a process by which
organisms become better adapted to
their environment. Natural selection is a process in which slight
variations, if useful, are preserved.
Abiotic and biotic factors contribute tonatural selection.
Natural selection ensures that the fittestorganisms survive and reproduce.
Fitness is a measure of reproductive
success.
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The Evidence Supporting Evolution
The fossil record yields some of the best
supporting evidence for the existence of
evolution.
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Common anatomical features in different
species support the theory of evolution.
Comparing homologous structures permits
scientists to determine evolutionary
relationships.
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The common biological makeup oforganisms also supports the theory of
evolution.
Studies of common developmentalpatterns supports the theory of
evolution.
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Experimental evidence
supports the theory of
evolution by naturalselection.
The study ofbiogeography helps
explain evolution.
Biogeography is the
study of thedistribution of plants
and animals
worldwide.
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Early Primate Evolution
Humans belong to the ordercalled primates, which
includes two suborders:
Prosimians (premonkeys
Anthropoids (monkeys,apes, and humans.
The prosimians probably
evolved from tree-dwellingmammals that lived during
the age of the dinosaurs.
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Primates are characterized by graspinghands, forward-looking eyes, and large
brains.
The fossil evidence of primate evolution
is limited, making it difficult to determine
the exact progression of early human
ancestors.
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Evolution of the Australopithecines
The earliest hominids were members of the genus
Australopithecus.
The oldest known australopithecine skeleton, named Lucy, is
believed to be about 3.5 million years old.
The skeleton belongs to a group calledAustralopithecus
afarensis and stood about
3 feet high.
About 3 million years ago,A. afarensis was replaced byA.
africanus.
A. robustus appeared approximately 2.3 million years ago, andA. boiseiappeared approximately 2.2 millions ago.
Australopithecines disappeared about
1 million years ago; no one is sure why.
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Evolution of the Genus Homo
The first truly humanlike creatures were
Homo habilis.
Homo habilis gave rise to Homo
erectus.
H. erectus moved from Africa to Europe
and Asia.
Homo erectus is believed to be the direct
ancestor ofHomo sapiens.
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Modern humans belong to Homosapiens.
Homo sapiens emerged about 300,000years ago
Homo sapiens consists of two subspecies:
Homo sapiens neanderthalensis (the
Neanderthals Homo sapiens sapiens
Cro-Magnons are the earliest knownmembers ofH. sapiens sapiens.
The Neanderthals disappeared about40,000 years ago.
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Human races result from variations
caused by geographic separation.
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End of Chapter 23