Transcript Darwin and Natural Selection

Charles Darwin
1
Voyage of the Beagle
Charles Darwin
• Born Feb. 12, 1809
• Joined Crew of HMS Beagle,
1831
• Naturalist
• 5 Year Voyage around
world
• Avid Collector of Flora &
Fauna
• Astounded By Variety of
Life
2
Voyage of the Beagle
Darwin left England in 1831 and returned 5 years
3
later in 1836
The Galapagos Islands
• Small Group of Islands 1000 km West of
South America
• Very Different Climates
• Animals On Islands Unique
•Tortoises
•Iguanas
•Finches
4
The Galapagos Islands
• Finches on the islands resembled a
mainland finch
• More types of finches appeared on the
islands where the available food was
different (seeds, nuts, berries, insects…)
• Finches had different types of beaks
adapted to their type of food gathering
5
• Darwin worked for 22 years, until Thomas
Malthus proposed an idea that helped him.
- Malthus proposed that the human
population grows faster than Earth’s food
supply.
• This made Darwin realize that species struggle
to survive (competition/predation/mating/shelter)
• Only some individuals survive to produce
offspring
- So what determines which individuals will
survive?
• Darwin hypothesized that
there was a force in nature
that worked like artificial
selection. With the input
of Alfred Wallace, he
developed the theory of
Natural Selection.
-- Wrote On the Origin of
Species by Natural
Selection (1859)
Darwin’s
Theory of
Evolution
by Natural
Selection
•The unequal ability of individuals to
survive and reproduce leads to a gradual
change in a population, with favorable
characteristics accumulating over
generations (natural selection)
•New species evolve
8
• Evolution is the
slow , gradual
change in a
population of
organisms over
time
9
Natural Selection
• Occurs when organisms with certain
variations (traits) survive, reproduce, and
pass on their variations to the next
generation.
• 4 parts/steps
– Overproduction
– Variation
– Selection
– Adaptation
Natural Selection
•
Overproduction: Organisms produce more offspring than
can survive
–
•
Variation: Individuals within any population have
variations
–
•
Ex: A population of fish may vary in size, speed, or coloration.
Selection: Individuals with useful (favorable) variations
survive to reproduce and pass on their variations.
–
•
Ex: Fish can lay millions of eggs.
Ex: Faster fish can better escape predators
Adaptation: Over time, individuals with favorable
variations make up most of the population and may look
very different from their ancestors!