Bio 120: Lecture 6 Evolution & Natural Selection Page 1 of 2
See also: Evolution and Natural Selection handout
Evolution -
Genetic change in a population or species over generations.
Microevolution – changes in the gene pool of a population over time
Macroevolution
– evolution at or above the species level (e.g., origin of new species, mass extinctions)
Charles Darwin: Father of Evolution
1809-1882
Darwin’s voyage on the Beagle
Darwin’s reading material:
Charles Lyell
Principles of Geology
(1830)
• Uniformitarianism
– “the present is the key to the past”
The Galapagos Islands
And later…
Thomas Malthus
- On Population
• Population growth exceeds food supply
Darwin’s theory of Evolution
•
Species living today descended from ancestral species
- Descent with Modification
•
Evolution occurs through Natural Selection
Natural Selection:
Darwin’s observations:
1. Individuals within a population vary, and some of this variation is heritable
2. More individuals are born than can survive and reproduce
3. Individuals compete for limited resources
– e.g. food, space, mates
Darwin’s inferences:
1. Because of their different traits, some individuals are more likely to survive and reproduce in a given environment than others.
2. Over time, descendants of these survivors, having inherited adaptive traits , will be more abundant in the population.
This is natural selection .

Bio 120: Lecture 6 Evolution & Natural Selection Page 2 of 2
1859 – Darwin published the book, On the Origin of Species by Means of
Natural Selection
Adaptive trait (Adaptation) :
- a trait that increases the ability of an individual to survive or reproduce, in a given environment.
Natural selection example:
The peppered moth
Pre-industrialized Europe Post-industrialized Europe
2 points about Natural Selection
•
Is not a creative process
- works with existing variation.
•
Is not goal-oriented
- result varies with population and environment.
Channel Islands animals (island dwarfism):
Pygmy mammoth (Pleistocene) Channel Islands fox
Sexual selection
•
Intrasexual competition – competition between individuals of the same sex for access to mates
Example: elephant seal males compete for access to females
•
Intersexual choice – individuals of one sex “choose” their mates among the members of the other sex
Example: Sage grouse male mating display
– females choose the “sexiest” males
What is sexual dimorphism?