Download Notes 7-1

Notes 7-1
Charles Darwin
Changes Over Time
Darwin’s Voyage
• Charles Darwin was an English Naturalist
who sailed on the Beagle, from England to
the Galápagos Islands.
Darwin’s Vogage
• Saw Diversity in organisms (scientists have
now identified over 1.7 million species!!)
• A species is a group of similar organisms that
can mate to produce fertile offspring
• fossils
Compared Galapagos organisms with
South American organisms
• Found many similarities and differences
• Galapagos iguanas had sharp claws to grip
slippery rocks and eat seaweed
• South American iguanas had small claws to
climb trees and eat leaves
• Thought iguanas came from South America to
Galapagos islands and evolved (changed over
time)
Compared Organisms among the
different Galapagos Islands
• Different shells on turtles of different islands
• Variations in birds beaks (Darwins Finches)
due to what they ate
• Adaptations are traits that help organisms
survive and reproduce in its environment
• Example: Beaks of finches
• CAN YOU THINK OF OTHER EXAMPLES OF
ADAPTATIONS?
Who was Charles Darwin Video Clip:
• http://www.pbs.org/wgbh/evolution/educato
rs/teachstuds/svideos.html
Natural Selection
• Individuals best adapted to environment will
survive to reproduce, therefore pass on its
traits
• Nature is selecting for certain traits
• Overproduction, variation, and competition
affect the natural selection process
Changes Over Time
Overproduction and Variation
Changes Over Time
Competition and Selection
• Variations among turtles make some of them
better able to survive. Turtles that survive to
become adults will be able to reproduce.
How does evolution really work? Video
clip:
• http://www.pbs.org/wgbh/evolution/educato
rs/teachstuds/svideos.html
• Darwin thought that over long periods of
time, natural selection would lead to change
(evolution). Helpful variations would become
more common, and unfavorable variations
would slowly disappear.
• Environmental factors and genes affect natural
selection
The Story of the Peppered Moth:
Natural Selection at Work
Let’s begin by looking at some real data!
Table "A" represents data from a ten-year study of two varieties of the same
species of peppered moth. The numbers represent moths captured in traps for ten
consecutive years. The traps were located in the same area each year.
Table A:
YEAR
NUMBER OF LIGHT
MOTHS CAPTURED
NUMBER OF DARK
MOTHS CAPTURED
1
556
64
2
537
112
3
484
198
4
392
210
5
246
281
6
225
357
7
193
412
8
147
503
9
84
594
10
56
638
The Story of the Peppered Moth
The English peppered moth, can be found throughout
the English countryside. There are two varieties that
exist in the population that differ in coloration:
1. Light gray with splotches
2. All Dark
These moths feed at night and rest during the
daytime. Sometimes they rest on the trunks of trees
or rocks both of which are covered with a light gray
colored lichen (an algae and a fungus that live
together). The light variety of moth is camouflaged,
but the dark moths, are easy prey for birds. Why?
They stand out like a sore thumb.
Before the Industrial Revolution, the darker variety
was considered rare. Why? Because presumably they
were eaten by birds before they could reproduce and
pass the gene for darkness onto their offspring.
In the late 1800’s, pollution killed the lichen that was
found on the trees and rocks. With a lack of lichen,
the tree trunks were now darker (no longer a gray
color). The light moths now stood out among the dark
bark of the tree and the dark variety were concealed
from birds. As a result, the frequency of dark
individuals in the population began to increase (they
were more fit). They successfully reproduced and
passed the gene for darkness on to their offspring. By
the turn of the century, the population consisted
almost entirely of dark moths.
PreIndustrial
Revolution
After Industrial
Revolution
(Pollution killed
the lichen)
Summary: After 1800, dark moths
were reproductively favored (more
fit) because the light variety were
now more commonly eaten by birds and
therefore left fewer offspring. The
gene for light color was therefore
reduced in the population.
Let’s look at that data table one
more time!
Table A:
YEAR
NUMBER OF LIGHT
MOTHS CAPTURED
NUMBER OF DARK
MOTHS CAPTURED
1
556
64
2
537
112
3
484
198
4
392
210
5
246
281
6
225
357
7
193
412
8
147
503
9
84
594
10
56
638
BACTERIA
Why does evolution matter now?
Video clip:
• http://www.pbs.org/wgbh/evolution/educato
rs/teachstuds/svideos.html