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Evolution Notes Grade 11 Bio Unit 2
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Unit 2 of Grade 11 Bio taken in Ontario - Evolution notes
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Lamarck Challenged the fixed species idea but still a creationist
Proposed that species can change over time to better suit their environment -
INHERITANCE OF ACQUIRED CHARACTERISTICS:
Organisms use or lose a trait according to a need, repeated use causes enhancement, the
acquired traits are passed to the next generation Ie: stretching of the giraffe's neck
Charles Darwin's observations:
1. Distantly related species on different continents with similar niches have a similar
appearance
2. Island clusters had many closely related species with different niches and different
appearances
3. Fossils show that species change over time, what we see now is related to what was there
before
4. Species can go extinct but new ones arise
He was the first to propose that all life has descended from one or few common ancestors
over a long time
He saw the environment as the driving force of evolutionary change
Proposed the theory of NATURAL SELECTION
Natural Selection:
Organisms produce offspring with differences
There is a struggle for survival due to limited resources
The environment selects the most fit individuals to survive and reproduce -- survival of the
fittest
The environment is always changing, so the population either evolves along with it or goes
extinct
SOURCES OF EVIDENCE:
FOSSIL RECORD: rock deposits from around the world show the same trend from simple to
complex fossil forms
Prokaryotic cells-> eukaryotic cells -> 1st multicellular life -> 1st multicellular life -> 1st
multicellular animals -> animals with shells-> animals with vertebrae (fish) -> land plants ->
amphibians -> reptiles -> mammals -> birds -> primates -> hominids-> modern humans
Fish-> amphibians -> reptile -> birds and mammals -> humans
Intermediates are called transitional forms
Whale evolution steps from pakicetus:
Reduction and eventual loss of hind limbs
Elongated body (longer spine)
Fingers get longer and closer together
Head more in line with the spine
Vertebrae elongates vertically, making a more rounded back
Reduction of the semi circular canals in the inner ears
Elongated head and snout
Migration of nostrils upwards and above eyes
, COMPARATIVE ANATOMY: mutation can only modify existing structures, forming new structures
and functions, and harmful or energetically costly structures are reduced or eliminated
Divergent evolution: closely related groups develop different outward traits (appearances)
Convergent evolution: distantly related groups develop similar outward traits
Types of evidence to support divergent evolution:
1. Homologous structures: similar internal structures in different species that may be used
for a similar/different purpose
Ie: whales and pakicetus ear bones and tooth shape -- common descent with modification
Front limbs of amphibians, reptiles, mammals and birds
Mammals have ear bones, reptiles don’t (jaw bones)
2. Vestigial structure: similar structure in different species that has reduced or no function in
some species
Ie: in humans - ear muscles, appendix, tail bones, goosebumps, 3rd eyelid, wisdom teeth
in other organisms: leg bones in whales and pythons, some toes on the legs of 4 legged
runners (horses, pigs, dogs)
Evidence for convergent evolution:
1. Analogous structures: similar function or external appearance with different internal
organization
Selection can favour the development of a similar trait more than once: wings evolved 4
times - insects, pterosaurs, birds and bats
EMBRYOLOGY: many complex vertebrates (amphibian, reptile, bird, mammal) share some
similarity in their early embryonic stages to "simpler" vertebrates that appear earlier in the fossil
record Ie: development of arm & leg buds, and vital organs, the presence of ancestral fish-like
structures that are no longer present in the newborns (gill slits and a full tail)
New developmental instructions are simply layered on top of the ancestral ones ie: webbing in
between fingers
BIOGEOGRAPHY: the science that attempts to document and explain patterns of biodiversity
(both past and present) in different geographical locations
Observations:
-different continents have different species, even though they often show convergent evolution
in similar niches
-remote areas tend to have more unique species
Ie: cacti only found in the deserts of the Americas, unique finches and tortoises in the
Galapagos, penguins only found in the southern hemisphere, marsupials only in australia and
south america
Explanation: groups of organisms became separated or migrated to new areas through:
1. Plate tectonics (shifting continents)
2. Land bridges
Hence, natural selection occurs in each new environment, different variation and mutations
accumulate. The greater the separation in space and time, the more differences there will be
between species
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