Biology 102 Chapter 11 & 12 - Evolution & Natural Selection
Biological Evolution: changes in the characteristics of a population over time.
● Changes occur between generations.
● Changes are typically very minor and indetectable.
● Over thousands/millions of generations, these changes accumulate to produce extreme
phenotypic differences between ancestors and their descendants.
So Remember…
Population evolves Individuals do not
The subject of evolution can be approached at different scales
● Small scale-from generation to ● Large scale-ancestor and descendent
generation species
○ Microevolution ○ Macroevolution
○ Allele frequencies ○ Phylogenetic trees
Microevolution Macroevolution
Think of a population as a gene pool What causes it?
● All different genes ● Many, many years of microevolution
● Some alleles going extinct
● All different alleles of those genes
● New alleles arising through mutation
● The relative frequencies of the alleles
For example:
Mechanisms of Evolution
F - dark fur What causes the shift in allele frequencies?
f - light fur ● There are few different mechanisms.
● initial population has 57% F, 43% f. ● The main one is natural selection.
● after several generations, population is The environment "selects" who gets to reproduce
and pass on their genes
now 70% F.
Survival of the fittest
● average fur color has become darker = Fitness - ability to survive AND reproduce
evolution!
Natural Selection
Natural Selection has 3 requirements:
● Genetic Variation: traits under selection must be variable and heritable.
● Selective Pressure: environmental conditions that make some individuals more fit than
others.
● Reproduction: individuals with the best traits pass them on to the next generation.
1
, Biology 102 Chapter 11 & 12 - Evolution & Natural Selection
Charles Darwin
Developed the idea of natural selection as the mechanism for evolution
Published his ideas in 1859:"On the Origin of Species".
Influenced by:
● Observation of nature all over the world
● Domestic plants and animals
● Geology
● Economics
Other notable evolutionary thinkers
Jean Baptiste Lamarck: proposed a different for evolution before Darwin.
"inheritance of acquired characteristics"
We now know that this is mechanism is incorrect. Individuals do NOT evolve.
Alfred Russel Wallace: developed the idea of natural selection independently of Darwin.
Patterns of Natural Selection
Phenotype selected:
Type of Selection Against For
Directional one extreme other extreme
Disruptive average both extremes
Stabilizing both extremes average
2
Biological Evolution: changes in the characteristics of a population over time.
● Changes occur between generations.
● Changes are typically very minor and indetectable.
● Over thousands/millions of generations, these changes accumulate to produce extreme
phenotypic differences between ancestors and their descendants.
So Remember…
Population evolves Individuals do not
The subject of evolution can be approached at different scales
● Small scale-from generation to ● Large scale-ancestor and descendent
generation species
○ Microevolution ○ Macroevolution
○ Allele frequencies ○ Phylogenetic trees
Microevolution Macroevolution
Think of a population as a gene pool What causes it?
● All different genes ● Many, many years of microevolution
● Some alleles going extinct
● All different alleles of those genes
● New alleles arising through mutation
● The relative frequencies of the alleles
For example:
Mechanisms of Evolution
F - dark fur What causes the shift in allele frequencies?
f - light fur ● There are few different mechanisms.
● initial population has 57% F, 43% f. ● The main one is natural selection.
● after several generations, population is The environment "selects" who gets to reproduce
and pass on their genes
now 70% F.
Survival of the fittest
● average fur color has become darker = Fitness - ability to survive AND reproduce
evolution!
Natural Selection
Natural Selection has 3 requirements:
● Genetic Variation: traits under selection must be variable and heritable.
● Selective Pressure: environmental conditions that make some individuals more fit than
others.
● Reproduction: individuals with the best traits pass them on to the next generation.
1
, Biology 102 Chapter 11 & 12 - Evolution & Natural Selection
Charles Darwin
Developed the idea of natural selection as the mechanism for evolution
Published his ideas in 1859:"On the Origin of Species".
Influenced by:
● Observation of nature all over the world
● Domestic plants and animals
● Geology
● Economics
Other notable evolutionary thinkers
Jean Baptiste Lamarck: proposed a different for evolution before Darwin.
"inheritance of acquired characteristics"
We now know that this is mechanism is incorrect. Individuals do NOT evolve.
Alfred Russel Wallace: developed the idea of natural selection independently of Darwin.
Patterns of Natural Selection
Phenotype selected:
Type of Selection Against For
Directional one extreme other extreme
Disruptive average both extremes
Stabilizing both extremes average
2
