Transcript Natural Selection

Natural Selection
Who came up with this theory of
evolution?
Charles Darwin
Who was Charles Darwin?
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He Came up with the mechanism for evolution
He was from England
Attended medical school at 16 and dropped out
Attended theology school and dropped out
Became interested in biology
Joined a voyage on the HMS Beagle at age 21
Why was this voyage so important?
He came up with the mechanism for
evolution
Where did he go on his voyage?
• He sailed from England to the South Pacific and South
America
One special place he traveled to
was the Galapagos Islands
• About 600 miles west of Ecuador
Volcanic ash on an island
What evidence did he find on his
voyage that gave him this idea?
Finches (a type of bird)
Large ground Finch
Medium ground finch
Sharp beaked
ground finch
Other Finches
Cactus Finch
Small Tree Finch
What did he learn from the finches?
• That all the birds were very similar but
have slight variation in beak type, size or
color.
• The variations were mostly adaptations
specific for the island they lived on.
How did Darwins’ finches evolve?
1. The islands were connected and only
one finch existed
2. The islands separated and finches were
isolated on separate islands with
different environments
3. Over many years, new and different
species formed
Giant Tortoises of the
Galápagos Islands
Section 15-1
and on Pinta Island, tortoise necks
were somewhere in between
Pinta
Pinta Island
Tower
Marchena
Intermediate shell
Fernandina
James
Santa Cruz
Isabela
Santa Fe
Hood Island
Floreana
Isabela Island
Hood
Saddle-backed shell
On the desert-like Hood Island,
tortoises had long necks…
Dome-shaped shell
…while on the lush rainforest of Isabela Island,
tortoises had short necks…
After his voyage, Darwin spent a great
deal of time thinking about his findings.
Biology by Miller and Levine; Prentice Hall Publishing©2006
He began to wonder if animals living on
different islands had once been members
same species that had
of the ____________
developed different
_________ characteristics
after becoming isolated
_______ from one
another in different habitats.
The Galάpagos Islands are close together
but have very different _______.
climates
Some were hot and dry, with
little vegetation.
Others had more rainfall and were
rich in vegetation
Biology by Miller and Levine; Prentice Hall Publishing©2006
Each island had
unique
its own _____
_________
assortment of
plant and animal
species.
What is Natural Selection?
1. Organisms produce more offspring than
can survive (Overproduction).
2. There is variation in any population.
3. Variations may lead to survival or death.
4. Those organisms most capable of
surviving will reproduce and pass on
their genes. (Descent w/ Modification)
5. There is an environmental change.
6. A shift in the gene pool occurs.
Natural Selection—notes!
In order to occur, must have:
1. Variation—bell curve; unequal survival
rate. Some are better “adapted” to
survive.
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Causes: Reproduction, Mutations,
Recombination.
2. Overproduction—exponential growth;
more offspring produced than will survive
(due to competition).
3. Environmental Change (selective
pressure)
Selection Pressures:
Are living and nonliving factors in the environment that make life
“a constant struggle for survival” .
These drive the evolution of a species.
Selection Pressures determine who lives and who dies.
4. Descent with Modification—Over
time, natural selection results in
species with adaptations that are best
for survival & reproduction.
NATURAL SELECTION - a case study
by Peter & Rosemary Grant
• Medium ground finch of Galapagos Islands off Ecuador [Darwin's Finches*]
– lives on seeds, cracks them open via force of beak the Grant's studied
finches on Daphne Major, a small island (800 sq. yd)
• In 1977: Island had only 2mm of rain instead of normal 130mm...
drought resulted in a loss of 84% of medium ground finch population
– most died of starvation
– seeds of Tribulus cistoides, primary food source --> were hard to open
unless birds had large, deep beaks, [the survivors had deeper beaks]
• Natural Selection lead to increase in average beak depth of survivors (graph
of data*)
• Offspring of survivors in subsequent years had beaks 0.5mm deeper