BISC 102 Lecture Notes - Lecture 2: Pinus Contorta, Speciation, Medium Ground Finch

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Microevolution: Changes within species population
Not controversial, observed in nature and laboratory variation and
Speciation: Formation of new species
Also shown to occur in nature and laboratory
Macroevolution: Changes above species or genius level
Fossil record or origin of complex adaptations
Most controversial and focused on this category of change (not evolution)
Macro evolution: Artificial selection in guppies
A lot of variability but guppies are still guppies
Natural Selection: The differential survival and reproduction of variant individuals within a
population
The process by which individuals possessing a set of traits that give a survival
advantage in a given environment tend to leave more offspring to reproduce for the
next generation
Observable process
New species have been observed to arise from natural selection (Example:
microorganisms or birds or mosquitoes)
Selection Pressure
Direction of selection depends on whether a trait is an advantage or
disadvantage
Intensity of selection depends on the selection pressure (what percentage
of individual dies)
1) Individuals can’t evolve only populations of a species can evolve
2) Individuals do not select which genes to pass on, reproductions can pass on genes that
are advantages and disadvantages
3) Selection is adaptive (not random), but mutations are random (most maladaptive but
some not)
4) Selection is not purposeful or forward looking (Natural selection does not happen for a
predetermined reason) but operates in the present environment
Conditions for Natural Selection (For a trait in a population)
There is a heritable variation
The variation results in a fitness differential (can be an advantage or disadvantage)
Then the trait will evolve in that population by natural selection
Natural Selection can act on any heritable trait (a trait with genetic variation)
● Physical
Body shape, shape, colour patterns
● Physiological
Metabolic traits, immune systems, endurance
● Behavioral
Genetic components and also influenced by environmental factors
Natural Selection can create loss of function (Vestigial structures)
Fossil record is always incomplete
Example: Whale ancestors
Transitional: Fossils show that Cetaceans descended from land mammals
Legs became vestigial
Biological fitness: (Offspring) An individuals contribution of genes to the next generation
relative to other individuals in the population (Example: reproductive success)
Example: Genes contributed to next generation: Eye colour, hair, colour, height, muscle type.
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