charles darwin proposed a way how evolution works – how did creatures change over time? – by...
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Charles Darwin• Proposed a way how
evolution works– How did creatures
change over time?– by natural selection
• Collected a lot of evidence to support his ideas – 1809-1882– British naturalist
Charles Darwin
• English naturalist• 1831- Began 5 year voyage on HMS Beagle – Traveled to various places in South America and
to the Galapagos Islands– Detailed his observations, took specimens– Concluded that all living things are related• VERY CONTROVERSIAL
Galapagos Turtles
1859- The Origin of Species
• Other naturalists were developing the same theory that Darwin did.
• Even though he was afraid of the Church’s reaction to his book he wanted to get credit for his work.
What did Darwin’s Travels reveal
• The diversity of living species was far greater than anyone had previously known!!
• These observations led him to develop the theory of evolution by natural selection!!
2006-2007
Insect eaters
Bud eater
Seed eaters
Cactuseater
Warbler
finch
Tree
finc
hes Ground finches
Darwin & Evolution by Natural Selection
Robert Fitzroy
Voyage of the HMS Beagle• Invited to travel around the world– 1831-1836 (22 years old!)– makes many observations of nature
• main mission of the Beagle was to chart South American coastline
Voyage of the HMS Beagle• Stopped in Galapagos Islands– 500 miles off coast of Ecuador
GalapagosRecently formed volcanic islands. Most of animals on the Galápagos live nowhere else in world, but they look like species living on South American mainland.
800 km west of Ecuador
Many of Darwin’s observations made him wonder… Why?
Darwin asked:
Why were these creatures found only on the Galapagos Islands?
Darwin found…many unique species
present day Armadillos
Darwin found:
Evidence that creatures have changed over time
ancient Armadillo
Darwin asked:
Why should extinct armadillos & modern armadillos be found on same continent?
Darwin found…clues in the fossils
Darwin found:Different shells on tortoises on different islands
Darwin asked:
Is there a relationship between the environment & what an animal looks like?
Finch? Sparrow?
Woodpecker? Warbler?
Darwin found… birds
Finch? Sparrow?
Woodpecker? Warbler?
Darwin found:Many different birds on the Galapagos Islands.
He thought he found very different kinds…
Darwin was amazed to find out: All 14 species of birds were finches…
Finch? Sparrow?
Woodpecker? Warbler?
Finch? Sparrow?
Woodpecker? Warbler?
But Darwin found… a lot of finches
Large ground finch
Small ground finch
Warbler finch Tree finch
But there is only one species of finch on the mainland! Darwin asked:
If the Galapagos finches came from the mainland, why are they so different now?
Finch? Sparrow?
Woodpecker? Warbler?
The finches cinched it!
Large ground finch
Small ground finch
Warbler finch Tree finch
Big seed eater Small seed eater
Insect eater Leaf & bud eater
Darwin said:
Ahaaaa! A flock of South American finches were stranded on the Galapagos…
Darwin found: The differences between species of finches were associated with the different food they ate.
different beaks are inherited variations
serve as adaptationsthat help birds compete for food
these birds survive & reproduce
pass on the genes for those more fit beaks
over time nature selected for different species with different beaks
Relationship between species (beaks) & food
Darwin’s finches• Darwin’s conclusions – variations in beaks • differences in beaks in the original flock• adaptations to foods available on islands
– natural selection for most fit• over many generations, the finches were selected for
specific beaks & behaviors
– offspring inherit successful traits• accumulation of winning traits:
both beaks & behaviors
– separate into different species
Warbler finch
Woodpecker finch
Small insectivorous
tree finchLarge
insectivoroustree finch
Vegetariantree finch
Cactus finch
Sharp-beaked finch
Small groundfinch
Mediumground finch
Large groundfinch
Insect eaters
Bud eater
Seed eaters
Cactuseater
Warbler
finch
Tree
finc
hes Ground finches
variation natural selection for best survival & reproduction
From 1 species to 14 species…
Lamarck - Theory of acquired traits
• Organisms develop traits during their lifetime and pass on those traits to their offspring
Malthus
• Reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone
• LaMarck– evolution by acquired traits
• creatures developed traits during their lifetime
• give those traits to their offspring
– example• in reaching higher
leaves giraffes stretch their necks & give the acquired longer neck to offspring
– not accepted as valid
Earlier ideas on Evolution
Darwin’s view of Evolution• Darwin– giraffes that already
have long necks survive better
– leave more offspring who inherit their long necks• variation• selection & survival• reproduction &
inheritance of more fit traits
Darwin’s Postulates
• There is variation among individuals
• Like begets like (traits are inherited)
Postulates cont’d
• Some individuals are most successful at surviving and reproducing than others
• Survival and reproductive success are not random – some characteristics enhance probability of success
Upshot of Darwin’s Postulates
• Those characteristics more common in next generations
=CHANGE
Artificial Selection • nature provides variation, humans select
variations that are useful. • Example - a farmer breeds only his best
livestock
Natural Selection
• The traits that help an organism survive in a particular environment are “selected” in natural selection.
• “Survival of the fittest”
Peppered Moth
Natural Selection and Species Fitness
• Overtime, natural selection results in changes in the inherited characteristics of a population.
• These changes increase a species fitness (survival rate)
Evidence for Evolution
• Homologous Structures
• Embryology
• Fossil Record
Homologous Structures
Embryology
Fossil Record
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