ARCH 131 Lecture Notes - Lecture 2: Wood Bison, Plains Bison, European Bison

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ARCH 131 Lecture 2 Notes:
Theory of Evolution, History & Fundamentals
Change is Constant
Extinct Species
Variation within Species
North American Bison & European Bison
Incredible Biological Variation
Species: 20,000 of butterflies, 24,000 spider, 400,000 beetles!!!
John Ray (1627-1705)
Naturalist, interested in variability
Species concept (look similar, can interbreed) (and genus)
Linnaeus (1707-1778)
Taxonomy and binomial nomenclature
George Buffon (1707-1788)
Typical renaissance man, wealthy
Species adapt slightly to new conditions
Lamarck:
“Inheritance of acquired characteristics”, giraffe necks
Evidence for Evolution
Charles Darwin (1809-1882)
Planned to become a priest, but studied liberal arts during theology
Offered a position to be the naturalist for a 5 year worldwide voyage (HMS Beagle, 1832-1836),
completes his education during the voyage.
Included all over south america, horn of africa, Oceania
Took many notes, pieces of specimens to study upon return (observed the correlation between the fossil
record and living organisms; such as the Megatherium, you only find their skeletons where you find the
south american sloth)
Animals of the Galapagos Islands
Finches: found variation in the 13 species of finches, collected specimens of
each one (killed, stuffed, sent) these variations were correlational to WHAT the finches ate
Traits: Habitat (tree, warblers, ground), Bill Shape (parrot like, grasping, probing,
crushing), Diet (fruit, insects, cactus, seeds)
Tortoises: tortoises that lived on lush island with a lot of vegetation are shaped
differently (low head to eat low vegetation), on dry island they have big necks to eat higher foods
Cactuses on dry island evolved to be taller to avoid being eaten, tortoises evolved larger
necks (arms race)
Natural Selection
Most basic foundation of biology today
Our understanding of NS has changed a bit since Darwin
6 Fundamental Premises of Natural Selection
1. More offspring are produced by a species that can be supported by naturally available food sources (fact)
a. Species produce more offspring that can survive
b. Thomas Maltheus (1766-1834):
i. “An Essay on the Principles of Population” (1798) “...animal populations tend to increase
exponentially while food supplies tend to remain stable.”
2. Within any one species there exists a significant amount of biological/genetic variability (fact)
a. Humans have one of the lowest amounts of genetic variability among animals
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3. Individuals with advantageous traits will have an edge over other members of their species in terms of
their ability to survive longer
a. Faster running Gazelles escape predators, flowers with more attractive scents
spread their pollen, Owls with better vision catch more prey etc.
4. Those individuals with traits that will increase their chance of living longer are more likely to reach the age
at which they will begin reproducing and so are more likely to contribute offspring to future generations.
a. They will pass on their advantageous traits, giving an advantage
5. Those traits that are advantageous under current environmental conditions will tend to be passed on.
a. Tigers, vertical stripes provide camouflage in areas with tall grasses to catch prey
BUT different environments change this, such as in a rocky area, they stand out and have less
chance of catching prey and could be replaced by a new version of tigers.
b. Animals that are unable to adapt to new circumstances can go extinct.
c. An individual's reproductive potential and reproductive success are products of
their ability to adapt to specific environmental conditions, which will select for certain traits or
characteristics
6. Over long periods of time, accumulated changes within a species will eventually result in new species.
This is called speciation.
a. Starting with subspecies
i. Wood bison (bison bison athabascae) and plains bison (bison bison bison)
ii. Will begin to diverge even further and look even more different, to make eventually,
separate species. North American bison are fatter, European Bison are very muscular.
iii. Eventually, different genera (plural of genus) resulting in Aurochs (now extinct)
b. This process is aided by geographic isolation (i.e a river)
Other Fundamental Components of the Evolutionary Process
Of the inherent variability in traits of a species (#2), most represents neither potential advantage nor
disadvantage to their survival, neutral traits
Of the variability, a very small percentage of the traits can be advantageous, a
very small percentage can be advantageous
Natural selection only acts on the variation that already exists in a species, doesn’t grant organisms what
they need
A common misconception about evolution is that it is moving in a specific, purposeful direction
Natural selection can only act on genetic variability (Lamarck was wrong, as genetic coding is necessary
to inherit traits)
Natural Selection can only play a role in the selection of traits that affect the reproductive success on an
individual (but that’s almost anything)
Unique (just whales and guppies) human female characteristic of menopause,
why did we inherit this? Because having babies when you’re older is dangerous, and ensuring the
successful lives of your children is important.
Micro- and Macro-evolution
Micro-evolution: short spans of time, development of limited change, can result in sub-species
Ground squirrel + tree squirrel
Macro-evolution: long spans of time, lots of change, many differences between organism that were once
of the same species
Elk + moose (deer), squirrel + beaver, chimp + bonobo
How does Speciation Occur?
Speciation occurs mostly by Adaptive Radiation: species spread to a variety of environments and, either
throughout geographic barriers or just sheer difference, different groups fail to continue to breed and so
gradually diverge into new species
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