1.
You have learned that both biotic and abiotic
factors affect ecosystems. Give some examples of
each and explain how biotic and abiotic factors
could have affected the tortoises that Darwin
observed on the Galapagos Islands
CH 16 DARWIN’S THEORY OF EVOLUTION
16.1 Darwin’s Voyage of Discovery
Evolution


The process of change over time
Change in allele frequency in a population over
time.


Geologists were suggesting that Earth was ancient
and had changed over time
Biologists were suggesting that life on Earth had
also changed.
Darwin’s Epic Journey
Darwin was invited to sail on the HMS Beagle’s fiveyear voyage mapping the coastline of South
America in 1831
 Darwin planned to
collect specimens
of plants and
animals on the
voyage.

Observations Aboard the Beagle
1.
2.
3.


Species vary around the world
Species vary locally
Species vary over time
Darwin wanted to explain the biological diversity
he observed in a scientific way
He looked for larger patterns into which his
observations might fit.
Species vary Globally


Darwin found flightless, grounddwelling birds called rheas living in
South America
Rheas look and act a lot like
ostriches (live in Africa).
Species vary Locally


These islands are close to one another, yet they
have different ecological conditions
Different islands had distinct tortoises,
mockingbirds, and finches.

Isabela Island has high peaks, is rainy, and has
abundant vegetation that is close to the ground
 Tortoise

has a dome-shaped shell and short neck
Hood Island is flat, dry, and has sparse vegetation
 Long
neck and a shell that is curved and open around
the neck and legs allow them to reach sparse, high
vegetation.

Darwin also observed that different islands had
different varieties of mockingbirds
 All

were similar to those in South America
Darwin noticed several types of small brown birds
on the islands with beaks of different shapes
 He
didn’t think they were important.
Species Vary Over Time

Darwin collected fossils
 Preserved remains
or traces of
ancient organisms

Some fossils of extinct
animals were similar to living
species.





Darwin collected MANY specimens
He actually kept poor records
Darwin sent plant and animal specimens to experts
for identification
Mockingbirds turned out to belong to three
separate species unique to the Galapagos
The little brown birds were actually all species of
finches.

Some specimens he took back to England were
living.
Putting the Pieces Together



Darwin began to wonder if different Galápagos
species evolved from South American ancestors
He spent years researching and filling notebooks
with ideas on species and evolution
Evidence suggested that species are not fixed and
that they could change by some natural process.
1.
2.
3.
Using a world map and page 381, count the
number of lines of 10° latitude the Beagle
crossed
Using the biome map from Ch 4 as a reference,
identify three different biomes Darwin visited on
his voyage
How did the geography of Darwin’s voyage give
him far greater exposure to species variability
than his fellow scientists back home had?