BIOL 2040 Lecture Notes - Lecture 1: Mutation, Immune System, Grappling Hook
27 Apr 2018
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Lecture 1 - Intro to Evolution
January 9, 2018
8:21 PM
What is Evolution?
• Many definitions are focused on the past, on the historical content
• Darwin's definition is that evolution is a descent with modification
o Descent suggests something changing from one into another, from the past to the present
• Biological evolution is a change over time in the proportions of individual organisms differing
genetically in one or more traits
o There is a change over successive generations - changes from one generation to the next,
not changes within a generation
• Changes transpire:
o By the origin and subsequent alteration of the frequencies of genotypes from generation to
generation within populations
• The change may cause a shift in how common the genotype is from one generation to
the next
o By alterations of the proportions of genetically differentiated populations of a species or by
changes in the numbers of species with different characteristics, thereby altering the
frequency of one or more traits within a higher taxon
Adaptation
• Sometimes called Darwin's Postulates
• There is variation
o Not all species look, behave, etc., the same
• Some of the variation is heritable
o Offspring tend to look like parents
• Not all individuals can survive/reproduce
o Some of the variation affects survival and/or reproduction
• Traits which enhance survival and/or reproduction will become more common
Divergence
• Different populations occur in different places and/or under different ecological conditions
• Populations in different places tend to not mate with one another and/or it is difficult/impossible
to be well adapted to all sets of conditions
o If a population is well adapted to one condition, they may not be able to adapt well in
another condition
• Populations will each adapt to their separate conditions, and will thus become different from
one another
A Critical Point
• Variation occurs before selection
o If a variant doesn't exist, it can't be selected for, no matter how beneficial it might be
o Selection does not cause variation, but it 'filters' certain traits
• Mutation generates variation at random
o There is no mechanism where beneficial mutations are more likely to occur than less
beneficial mutations - it just occurs randomly
• Selection is not random, although it also has no foresight
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