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Changes in a population of organisms over time.
Charles Darwin
A. Born 1809
B. Took a trip around the world on the HMS
Beagle – Acted as the ship’s naturalist
C. Came up with the Theory of Evolution
D. He traveled to the Galapagos Islands
1. Where Darwin did his most persuasive
2. Discovered an example of:
speciation : members of a species stop
breeding with one another until
two separate species are formed.
How It Happens
 Geographic Isolation: Two populations
within a species are separated by some
natural barrier.
 Temporal Isolation: populations within a
species mate at different times.
 Behavioral Isolation: Members of one sex no
longer find certain varieties of the other sex
suitable for mating.
Introduction of Adverse
Environmental Conditions
 Could be a predator, new landscape, climate
or anything else that changes the
requirements for survival.
 Disruptive Selection: Something is causing
the death of part of the mean of the
population. Can cause speciation
 Directional Selection: One characteristic is
being reduced and another type is more
successful. Results in a population that would be
more like those with the favorable trait.
 Stabilizing
Selection: The
outliers have
trouble surviving
Results in a
population that
has DNA (traits)
like the average
of past generation
 Artificial Selection: Man chooses which
specimens will pass their genes on to the next
More Evidence for Evolution
 Homologous Structures: Structures that arise
from the same tissue but have different
 Analogous Structures: Structures that arise
from different tissues but have the same
 Vestigial Structures: The reduced form of a
structure that is no longer providing a
reproductive advantage.
Dating Techniques
 DNA Molecular Clock: A technique that uses
fossils and rates of molecular change to
deduce the time in geologic history when two
species diverged.
 Other Absolute and Relative Dating Methods…
Evolution: An Overview
 “Survival of the Fittest”
 Fitness is a NUMBER = How many kids did
you have that survived to reproductive
 The TRAITS that survive are the ones that
were passed on to the next generation.
 If a trait helps you to have more kids  more
individuals in the next generation have the
DNA for that trait