- Before 1850, most people believed the Earth was only a few thousand years old and never changed, with species fixed to their environments. - Jean-Baptiste Lamarck proposed one of the first theories of evolution, suggesting species evolve through inheritance of acquired characteristics. - Charles Darwin's observations on his voyage on the HMS Beagle led him to propose natural selection as the mechanism of evolution, where individuals better suited to their environment are more likely to survive and pass on their traits. - Darwin observed related but distinct finch species in the Galapagos Islands, supporting the idea that isolated populations can evolve into new species over time through natural selection.

2. History of Evolutionary Thought
Before 1850, most people believed…
– Earth formed by supernatural events and never changed.
– Earth only a few thousand years old.
– Each species was made to fit its environment.
– Species never changed and did not go extinct.

3. History of the Idea of Evolution
Jean Baptiste Lamarck
Proposed that species
DO evolve
***PROPOSED
EVOLUTION
OCCURRED BY
INHERITANCE OF
ACQUIRED
CHARACTERISTICS

4. Lamarck
Lamarck’s Hypothesis:
1. Desire causes change
Ex.) ancestors of birds had a desire to
fly, so they did.
2. Use and Disuse
Ex.) If species used its arms to swim
over and over, it would develop flippers.
If not, flippers would disappear.
3. Traits acquired during life can be
passed on
Ex.) Michael Jordan’s children will be
great basketball players.
WRONG!!!!

5. History of the Idea of Evolution
Alfred Wallace
English teacher who
collected plants and
insects.
Observed variations
in organisms
Proposed that
species DO change
over time

6. Charles Darwin
At 22, sailed on the “HMS
Beagle” to the Galapagos
Islands.
Was going to school to be
a minister-believed God
created each species to
match its habitat and they
never changed.
Thought Earth was about
6,000 years old and didn’t
change.

7. Charles Darwin cont.
During journey, he made
observations and
recorded them in a
journal.
Darwin began to doubt
that species remained
“constant.”

8. Scientific Theories
Hypothesis: a testable
explanation for an observation
“Theory” in layman’s terms = a
guess and this is NOT the same
as a scientific theory.
Scientific theory:
Accepted as factual
NO EVIDENCE AGAINST IT!

9. Evolution
EVOLUTION IS A SCIENTIFIC
THEORY!
Not a hypothesis, or an
educated guess
Unending amount of evidence to
support it
Evolution is called “the
unifying principle of Biology”
Isn't Evolution JUST a Theory?

10. Types of Evolution
Evolution - genetic change of a population of organisms
over time- descent with modification
Microevolution:
Small genetic changes of a population
Can occur in shorter amount of time

11. Natural Selection
Natural selection: process by which organisms best
suited to their environment survive and reproduce.
– Darwin’s proposed mechanism of evolution
– Nature “selects” which members of a species will
succeed in struggle for existence.
– Survival depends on the particular environmental
conditions a species finds itself in.
– If the environment changes, so do the populations
that live there.
Adaptation: using inherited genetic characteristics to
increase chance of survival in new environment.

12. Natural Selection
Three conditions necessary for natural selection to occur:
1. Genetic variation: Individuals within a population must be
genetically different. This is due to mutation.
****Random mutations are the raw material for evolution to occur!!!!!!!
1. Overproduction of offspring: More organisms are born than
can survive.
2. Differential reproduction: Certain traits enable individuals to
survive and have more offspring than others.—SURVIVAL OF
THE FITTEST
Result: Genes that help a species survive stay in the gene pool.
“Unfavorable” genes gradually decrease. This causes
changes in gene frequencies EVOLUTION!!!!!
Evolution: How Does Evolution Really Work?

13. Natural Selection Example
The industrial revolution
– In England in the early 1800’s industry boomed
– Factories, trains, smoke and smog
– Peppered moths were dark or light colored, and
the dark ones that were once rare became more
common.
– Hypothesis?

14. The Peppered Moth
– Kettlewell tested this hypothesis
Released equal numbers of moths in polluted
AND clean forests.
In industrialized areas, dark gray moth was
better camouflaged.
They survived, had more offspring
– The population *as a whole* evolved to be
better suited to the environment more gray
and camouflagedADAPTATION!
– This is an example of microevolution

15. The Peppered Moth

16. Types of Natural Selection
1. Directional selection
2. Stabilizing selection
3. Disruptive selection

17. Types of Natural Selection
Directional selection- individuals at one end of
the curve are favored so they contribute more
offspring so the curve shifts in one direction .
Directional selection

18. Types of Natural Selection
Stabilizing selection- average individuals are
favored so the middle of the curve increases.
Stabilizing Selection

19. Types of Natural Selection
Disruptive selection- individuals at both extremes
are favored so they contribute more offspring and
two peaks result over time.
Disruptive selection

20. Darwin and the Finches
Darwin traveled to the Galapagos and
took interest in the finches.
He noticed the finch species on the
islands were different, but all resembled
one from S. America.
Darwin thought some migrated and new
species evolved. This is what he
proposed:

21. Darwin’s Finches
Finches migrated from
S. America to the
islands
– Populations on different
islands adapted to
different environments
and food sources they
found there.
– Microevolution and
mutations accumulated
so populations on the
different islands became
more and more different.
Divergence: the
accumulation of
differences between
species or populations.

22. Darwin’s Finches
Over time the populations on the islands became
so different they no longer mated-different species
– Several new finch species evolved from a
common ancestor from S. America
– Speciation: the formation of a new species
through accumulated changes.
– This is an example of macroevolution

23. Another Example of Speciation
Geographical isolation: members of a
population are separated geographically 
leads to speciation.
– Due to volcanoes, earthquakes, flooding, etc.
– Can lead to divergence and then speciation.

24. Artificial Selection
Artificial selection: human intervention in animal or
plant reproduction to ensure that certain desirable
traits are represented in successive generations.
Instead of NATURE selecting which traits are
favorable, HUMANS select the favorable traits.
Ex. dogs or racehorses