Download Chapter 15

Evolution – change over time. It is the
process by which modern organisms
have descended from ancient
organisms.
 Current scientific facts, observations and
hypotheses all combine to create
current evolutionary theory – which is a
well-supported, testable explanation of
the biological diversity on Earth.

Charles Darwin
Born on Feb. 12, 1809 (same
day as Abraham Lincoln).
 Came from a family of
doctors so he was sent to the
University of Edinburgh but
found surgery disturbing so he
dropped out.
 His father then sent him to
Christ’s College, Cambridge
to become a Anglican
minister. He was more
interested in natural history
and the sciences and
worked closely with
professors that allowed him
to be outside doing “field
work”.

Christ’s College, Cambridge
Darwin was recommended to sail on the H.M.S.
Beagle as a companion to the captain.
 The voyage lasted 5 years and sailed around the
world. Darwin eventually become the ship’s
naturalist, collecting specimens wherever they
went.
 The most important place that influenced Darwin
was the Galapagos Islands.

3 Main Observations
1. Patterns of Diversity –
 Darwin noticed that
species fit the environment
where they lived.
 But he was puzzled by
where animals lived and
didn’t live.
 Question? No rabbits in
Australia? No kangaroos in
Argentina?
2. Living organisms and Fossils –
 Darwin collected preserved remains of
organisms called fossils.
 Some fossils looked like current animals,
others looked completely different.
 Question: How were they related to living
species?
3. Galapagos Islands –
 Small islands located 1000km west of South America.
 Even though the islands were close together they had
very different climates.
Examples:
 1. Tortoises – longer


neck for sparse
vegetation. Shorter
neck where
vegetation was more
abundant.
2. Finches – Darwin
noticed that these
birds have different
shaped beaks
Question? Why
Nothing influenced Darwin more than his
visit to the Galapagos Islands.
 Darwin did not understand the reason for
the diversity but he observed that many
animals and plants varied noticeably
among the different islands of the
Galapagos.
 He began to wonder if they had once
been members of the same species.


Up until Darwin’s time most Europeans believed
that life on Earth was only about 2,000 years
old.

But during the 19th century, scientists were
gathering information that suggested that
Earth was very old.
Hutton – geologist
 Geologic processes form slowly so Earth was much
older than 2,000 years.
Lyell – geologist who wrote “Principles of Geology”
 We must explain past events from what we see today.
For example, earthquakes and volcanoes
Based on these geologists Darwin asked himself 2
questions.
1. If Earth could change, could life also change?
2. For life to change it must take many, many years which
would only be possible if Earth was old.
Lamarack – said that
use or disuse of
“organs” caused
organisms to gain or
loose certain traits
during their lifetimes
and then they could
pass them on to their
offspring.
 He used this to explain
how a giraffe got a
long neck – it
stretched!
What’s wrong with this?

He said that if human populations
continued to grow sooner or later there
would be insufficient living space and food
for everyone.
 This influenced Darwin because he realized
it applied to all plants and animals…..not all
offspring can survive…
 What factor determines survival and death?

Section 15-3 Darwin
Presents His Case
Darwin returned from the Galapagos and
begin writing about his discoveries.
 He was troubled by what he saw and his
understanding that species became
modified so he shelved his manuscript and
told his wife to publish it when he died.
 But in 1858, another scientist (Alfred
Wallace) started publishing results that were
similar to Darwin so in 1859 Darwin decided
to publish his results in a book called “On
the Origin of Species.”

Variation – Artificial Selection


Darwin knew that
variation was
important….not
unimportant defects.
His evidence was in
farming and animal
breeders of dogs and
horses. Breeders
choose traits they
wanted and bred for
them. We call this
Artificial Selection.
Evolution by Natural Selection
Definitions:
1. struggle for existence – members of a
species compete for resources
2. Fitness – ability to survive and reproduce
3. Adaptations – inherited characteristics that
increase an organisms chance of survival.
Natural Selection
– How it works!
Steps
V 1. Variation = organisms within
a population differ
O 2 . Organisms produce more
offspring than can survive.
C 3. Organisms compete for
limited resources.
S 4. Individuals best suited to their
environment survive and
reproduce most successfully
and pass on their traits to
offspring.
(Very, Often, Cars, Speed)
Natural
Selection
Example
Evidence for Evolution
4 pieces of evidence
1. Fossil Record – transitional
fossils show us intermediate
stages.
Example: horse and camel
Evidence for Evolution
2. Geographic distribution – similar
environments on different
continents yielded similar
anatomies and behavior because
they were exposed to the same
pressures of natural selection.
 We call this convergent evolution.
 Example: Flightless birds
Emu – Australia
Rhea – South
America
Ostrich - Africa
Evidence for Evolution
3. Homologous structures –When organisms have the


same structure that performs different functions.
They come from the same embryonic tissue.
Example: front limbs of animals
Vestigial structure – being reduced or eliminated in
size. Ex. wisdom teeth, appendix
Evidence of Evolution
4. Embryos – in the early
stages of development,
many vertebrates look
similar providing
evidence that they
shared a common
ancestor. (mutations
don’t occur early in
development or the
embryo would die)