Transcript Natural Selection

Natural
Selection
Charles Darwin
(1809-1882)
• Studied biology
• In 1831 at age 22, he accepted a job on the
HMS Beagle as a scientist
• The HMS Beagle docked at the Galapagos
Islands off the coast of South America
Charles Darwin
(1809-1882)
• Based on fossil evidence, Darwin knew plants
and animals change over time
• Believed organisms had changed slowly over
time and would keep changing
• The environment and adaptability of the
organisms controlled the changed.
What he saw in the Galapagos…
What he saw in the Galapagos…
• Each island had similar animals with slightly
different traits
– Long or short necked tortoises depending on the
plant height
What he saw in the Galapagos…
– Finches had
many different
beak sizes and
shapes
depending on
diet
Natural Selection
• Darwin’s theory that organisms changed over
time based on traits that helped them survive
• Survival of the fittest
Natural Selection
• Organisms with traits that help them survive
grow and reproduce passing on those traits to
their offspring
• Organisms with traits that don’t help them
survive are usually eaten or die and don’t pass
on their traits
Natural Selection
• Factors that can affect the process of natural
selection
– Overproduction of offspring in a species
– Competition among organisms of same species
– Genetic variations within a population
Peppered Moths
• In England there is a species of peppered
moth
• They come in two color variations
– Light
– dark
• The trees they lived on had a light bark color
• During the industrial revolution, factories
were built that produced soot
• The soot stained the tree bark black
Peppered Moths
• Use the moth and bark pictures on your desk to
answer.
• Which moths were better adapted to the trees before
pollution? light
• Which moths were adapted to the trees after the
pollution? dark
Elephant Example
• Let’s say a group of elephants had mostly
short trunks
• But a few of the elephants in the group had
slightly longer trunks than others
• When food and water became scarce, the
elephants with longer trunks could reach
higher for food and deeper into holes for
water
Elephant Example
• Elephants with shorter trunks would die of
thirst and starvation
• Elephants with longer trunks would survive
and reproduce passing on their longer trunks
• Over time, the group would consist mostly of
long trunked elephants
Elephant Example
• Put the elephant cards in the right order