Download Darwin & Evolution by Natural Selection

Darwin & Evolution
by
Natural Selection
Cactus
eater
Insect eaters
Seed eaters
Bud eater
2006-2007
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
Darwin’s Life
• Darwin took a convoluted path on his way to
developing his theory.
• His first career was to be a doctor, but he
could not stand being around blood
• He then studied to be a pastor- his plan was to
preach and study nature as a hobby
• After completing school, he was invited to
serve as a doctor/naturalist on an incredible
voyage
Introducing… the trip that changed it all…
• In 1831, Darwin set sail on the Beagle for a voyage around the
world
• During his travel, Darwin made numerous observations and
collected evidence that led him to propose a revolutionary
hypothesis about the way life changes over time = The
Theory of Evolution
• Darwin was interested in the diversity of organisms in specific
areas and the specific locations species inhabited
– How are there so many different organisms and why do
they live in specific areas?
• Darwin used these observations to scientifically explain the
diversity of life on this planet.
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
Robert Fitzroy
Darwin found…clues in the fossils
During his trip, Darwin
found:
Evidence that creatures
have changed over time
present day Armadillos
Darwin asked:
ancient Armadillo
Why should extinct
armadillos & modern
armadillos be found on
same continent?
Voyage of the HMS Beagle
• Stopped in Galapagos Islands
– 500 miles off coast of Ecuador
Galapagos
Recently 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
Darwin found…many unique species
Darwin asked:
Why were these
creatures found only on
the Galapagos Islands?
The Galapagos Islands
• Darwin observed that the characteristics of many animals and
plants varied noticeably among the different islands.
– Why were these close islands inhabited by similar organisms
that appeared slightly different?
– Did these species evolve from a common ancestor after
being isolated to different islands needing different survival
skills?
Pinta Island
Intermediate
shell
Hood Island
Saddlebacked shell
Isabela Island
Dome-shaped shell
Darwin found… birds
Darwin found:
Many different birds on
the Galapagos Islands.
He thought he found very
different kinds…
But Darwin found… a lot of finches
Darwin was amazed to
find out:
All 14 species of birds
were finches…
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?
Upon closer examination, Darwin found:
The differences between species of finches
were associated with the different food
they ate.
Simplified version of what happened

Original Group of finches migrated to islands with
some variation in beak characteristics.





different beaks are inherited variations
The beaks serve as adaptations
that help birds compete (or reduce competition) for
food
Best suited birds survive & reproduce
pass on the genes for those more fit beaks
over time nature selected for different species with
different beaks

Original Species separated into many new species
Relationship between species (beaks) & food
From 1 species to 14 species…
Warbler finch
Cactus finch
Woodpecker finch
Sharp-beaked finch
Small
insectivorous
tree finch
Large
insectivorous
tree finch
Small
ground
finch
Cactus
eater
Insect eaters
Medium
ground
finch
Seed eaters
Vegetarian
tree finch
variation
Bud eater
natural selection for best
survival & reproduction
Large
ground
finch
Not Just Finches
Original
And then he thought…. and thought
some more….
• Over the next 20 years Darwin spent much of
his time thinking about the differences he had
observed in living organisms during his travels.
– He found that all the organisms he had sampled
on the Galapagos, were distinct species different
from those found on the mainland.
– There were also different species found on each
island in most cases.
Darwin’s Hobbies…
• Darwin also saw that humans choose organisms
with specific characteristics- Breeding organisms
with specific traits in order to produce offspring
with identical traits is called artificial selection.
• He spent a lot of time studying varieties of pigeons that
had been bred
• Darwin hypothesized that there was a force in nature
that worked like artificial selection.
– This force would “work” on the differences between
organisms, just like a breeder picks out the best
specimens to breed.
The tipping point.
• Finally in 1858, Darwin received a letter from another
Naturalist- Alfred Russel Wallace.
• Wallace was a naturalist that had spent a lot of time in
the Amazon, and the Malaysian Archipelago
– He, like Darwin had noticed the variations in animals
between islands and the main lands
• Wallace’s letter detailed an idea he had been
considering:
– Species change overtime, this change occurred in order for
organisms to adapt to their environment.
• Wallace had independently arrived at the same
conclusions that Darwin had considered.
The founders of Evolutionary Theory
• Darwin realized it was time to publish his
work.
• He presented some of his own conclusions,
along with a paper written by Wallace at a
scientific meeting.
• Within 18 months, Darwin had published: On
The Origin of Species
Evolution by Natural Selection
• It was proposed that living things evolve as
the result of:
– Natural Variation
– The struggle for existence
– The survival of the fittest
– The descent with modification
Peacock tail evolution:
http://www.pbs.org/wgbh/evolution/library/01/6/l_016_09.html
Natural Variation
• Darwin and Wallace both stated that
organisms in nature had variation
– Differences among individuals of a species
What do we know?
• Populations are a mix of different individuals
• How do we know this? OBSERVATION
Variation
Struggle for Existence
• Darwin was convinced artificial selection worked in
nature as the result of overproduction and
competition for resources = struggle for existence
– Overproduction- organisms produce more young
than the environment can support
– Competition for resources- members of each
species compete regularly to obtain food, living
space, mates, and other necessities of life
Survival of the Fittest
• Fitness= an individual’s ability to survive and
reproduce in it’s environment
• Fitness results from adaptations
– Adaptations = inherited characteristics that increase
an organism’s chance of survival
– = “Survival of the Fittest!”
Survival & Reproduction of the fittest
…the fittest!
the traits that help an organism fit the
environment better to survive & reproduce
Survival & reproduction of the fittest bug…
Natural Selection
• Survival of the fittest = Natural Selection!
– Traits are being selected and increasing over time
(over many generations without human
influences)
• Over time, natural selection results in changes
in the genetics of a population. These changes
increase a species’ fitness in its environment.
What determines survival?
• Natural Selection- the environment
removes individual that are not fit enough
to survive
– traits that help individuals survive
•
•
•
•
survive predators
survive disease
compete for food
compete for territory
Adaptations
– traits that help individuals reproduce
• attracting a mate
• compete for nesting sites
• successfully raise young
Survival & Reproduction of the Fittest
Summary of Darwin’s Theory
• Individual organisms in nature differ, and some variation is
inherited
• Organisms in nature produce more offspring than can survive
and reproduce
• Members of each species compete for limited resources
• Unique organisms have different advantages and
disadvantages in the struggle for existence
• Individuals best suited to their environment survive and
reproduce, passing the characteristic to their offspring.
Individuals without the characteristic die
• Species change over time due to natural selection… new
species arise and others disappear
• Species alive today have descended with modification from
species of the past
• All organisms on Earth are united by a common descent
Darwin proposed natural selection as the
mechanism of evolution
• In summary:
• Darwin saw natural selection as the basic mechanism of
evolution
• Survival of the Fittest: Darwin concluded that individuals
best suited for a particular environment are more likely to
survive and reproduce than those less well adapted
– As a result, the proportion of individuals with favorable
characteristics increases
– Populations gradually change in response to the
environment
• Organisms without these variations are less likely to
survive and reproduce.