unit 5 – lecture 5. speciation speciation – creation of a new species could occur when organisms...
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Unit 5 – Lecture 5
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SpeciationSpeciation – creation of a new species
could occur when organisms of the same species can no longer interbreed in their natural environmentexplains how tigers and lions can
interbreed but are not of the same species – not in same environment
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SpeciationCauses for speciation:
geographic isolation – physical separation of populations lead to each changing separately
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SpeciationCauses for speciation:
reproductive isolation – caused by:fertilization prevention creation of sterile hybrids [mule/hinny]
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SpeciationCauses for speciation:
reproductive isolation – caused by:behavioral differences
nocturnal/diurnal, blooming seasons, mating rituals or choices, etc
simple physical incompatibilities.
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Change over TimeTwo ways of hypothesized evolutionary
change:gradualism – gradual changes
[microevolution] which would slowly build to change org. believed to be the major form of
evolutionary change transitions are rarely seen in the fossil
record
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Change over TimeTwo ways of hypothesized evolutionary
change:punctuated equilibrium – long periods of
little change followed by short periods of intense changebecause of very “incomplete” fossil record
according to the theory of gradualism, created by Stephen J Gould
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Comparing TraitsComparing organisms from an evolutionary
viewpoint, they can be said to exhibit convergence or divergence.Convergent Evolution
organisms in similar environments have similar traits
makes sense –similar adaptations needed to function
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Comparing TraitsComparing organisms from an evolutionary
viewpoint, they can be said to exhibit convergence or divergence.Convergent Evolution
organisms which show convergence have analogous structuresanalogous structures – different
structures with the same use
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Comparing TraitsComparing organisms from an evolutionary
viewpoint, they can be said to exhibit convergence or divergence.Divergent Evolution
states that organisms which were once closely related become less similar over time because of geographic or reproductive isolation
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Comparing TraitsComparing organisms from an evolutionary
viewpoint, they can be said to exhibit convergence or divergence.Divergent Evolution
adaptive radiation – states that this change between species happens in a short amount of timebelieved to occur because of change in
location
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Comparing TraitsComparing organisms from an evolutionary
viewpoint, they can be said to exhibit convergence or divergence.Divergent Evolution
homologous structures – similar structures have a different useassumed to be caused by evolutionary
ancestry
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Comparing TraitsComparing organisms from an evolutionary
viewpoint, they can be said to exhibit convergence or divergence.Divergent Evolution
homologous structures – similar structures have a different useDNA evidence doesn’t always support
this theorysimilar structures are sometimes coded
for by very different genetic information
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Comparing TraitsVestigial Structures – multiple definitions:
previously – structures which no longer are thought to provide any benefit to organismslist of nearly 200 useless structures in
late 1800s to almost none now, leading to a re-vamping of the definition according to an evolutionary standpoint
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Comparing TraitsVestigial Structures – multiple definitions:
previously – structures which no longer are thought to provide any benefit to organismslist of nearly 200 useless structures in
late 1800s to almost none now, leading to a re-vamping of the definition according to an evolutionary standpoint
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Comparing TraitsVestigial Structures – multiple definitions:
previously – structures which no longer are thought to provide any benefit to organismslist of nearly 200 useless structures in
late 1800s to almost none now, leading to a re-vamping of the definition according to an evolutionary standpoint
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Comparing TraitsVestigial Structures – multiple definitions:
currently – structure which no longer serve in their capacity it is assumed that they hadbased off of comparing organs in
organisms comparing their uses to their hypothesized evolutionary ancestors
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Vestigial…or not?Appendix – breaks down cellulose in plants
serves as part of the immune system in humans to make white blood cells and antibodies to fight infection
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Vestigial…or not?Coccyx [tailbone] – continues into tail in
other orgshelps anchor muscles so that we can sit
and walk correctly – including the gluteus maximus
btw – humans born with “tails” do not have tails in the sense of typical orgs, they are just fleshy growths.
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Vestigial…or not?Pineal gland – secretes melatonin, an
important chemical to our sleep/wake cycles [what makes you feel sleepy]
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Vestigial…or not?Tonsils – part of immune system
minimizes respiratory infections, produces antibodies
first line of defense
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Vestigial…or not?Wings in flightless birds – not for flying…
but often used for balance or for sexual selection
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Vestigial…or not?“Junk” DNA – does not code for any traits…
found to have important functions in embryonic development, possibly for social functions, controlling expression of other genes
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Vestigial…or not?Eyes in blind cave animals like fish &
salamanders
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Vestigial…or not?Sexual organs in dandelions –
dandelions reproduce asexuallyvegetative reproductionseeds are asexually formed too
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Vestigial…or not?Wisdom teeth
human mouths now smaller than those even a few hundred years ago
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Vestigial…or not?Male nipples – certainly don’t nurse children
ALL humans are female during the first six weeks of development
around 6 weeks, certain hormones are dispersed which lead to further development of a certain sex.
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Vestigial…or not?There is no way to scientifically determine
the uselessness of an organ just that no function has been found – Darwin agreed.
As always, science can only work with available info and revise as necessary, which again stresses what science truly IS – the pursuit of knowledge about our world.