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On the Origin of Species

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Charles Darwin’s book
Published December,
1859
Sold out in one day
“A century and a half
later, it still argues the
case for evolution
better than any other
book. “ Edward J. Larson, Evolution
Darwin’s Case for Evolution
Artificial Selection
Darwin’s Case for Evolution
- Artificial Selection
An idea with which people were comfortable
 Farmers select for breeding only the animals or
plants that have the traits they like
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 Fast
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horses, plants with the biggest fruit
Named this process “artificial selection”
Darwin’s Case for Evolution –
Variety also exists in nature
– among species (interspecific)
Darwin’s Case for Evolution
-and within species
(intraspecific)
Darwin’s Case for Evolution
In nature, many more
individuals are
born than can
possibly survive.
Thomas Malthus connection
Darwin’s Case for Evolution
Why can’t they all survive?
Limiting Factors (factors that limit pop. size)

Predation
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Food supply
Shelter
Mates
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Competition
Darwin’s Case for Evolution
A high rate of reproduction combined with
competition for food, shelter, and mates
creates a struggle for existence.
The fiercest struggle is among individuals of
the same species sharing the same niche,
habitat, and dangers.
Darwin’s Case for Evolution
“Can we doubt that individuals having an advantage,
however slight, over others, would have the best
chance of surviving and procreating their
kind?...This preservation of favorable
conditions… I call Natural Selection.”
In modern terms:
DIFFERENTIAL REPRODUCTION OF
SELECTED PHENOTYPES
Natural Selection
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Measures the ability of a population to
survive and reproduce
Dependent upon environmental factors
Genotypes (alleles)
phentoypes (traits)
survival/repro
advantage!
Darwin’s observations
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High reproductive potential
Overall, population size is stable
Limited resources
Variation
Darwin’s conclusions
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Competition drives selection
Fitness level determined by adaptations!
The more adaptations… the more evolutionary
success!
Natural Selection Summary
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Populations of organisms struggle for survival
and reproductive success (fitness)
Environment determines which genetic
variations are most desirable in
organisms/populations
Populations of organisms adapt to their
environment to improve fitness
WHERE’S THE EVIDENCE?
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FOSSIL RECORD
BIOGEOGRAPHY
COMPARATIVE ANATOMY
COMPARATIVE EMBRYOLOGY
COMPARATIVE BIOCHEMISTRY
Darwin’s Evidence
Fossil Record

Over millions of years,
deposits compress older
sediments below into
layers

Older layers, with older
fossils, lie beneath
younger layers, with
younger fossils
Darwin’s Evidence
Fossil Record

embryology in extinct
organisms similar to that
in living organisms
Variation
Darwin’s Evidence
Morphology –
Similarities in the form and structure of organisms
Homologous structures:
 structures with
different mature
forms/functions, but
which develop from
the same embryonic
tissues
Darwin’s Evidence
Morphology – similarities in the
form and structure of
organisms
Analogous structures:

structures with same mature
forms/functions, but which
develop from the different
embryonic tissues
Homologous vs. Analagous
Darwin’s Evidence
Morphology –
Vestigial
Organs –
Homologous
structures
which no
longer
function
VESTIGIAL HUMAN
STRUCTURES ?
Darwin’s Evidence
Embryology
Similarities in patterns of development among different
species today suggest common ancestor:
Chick
Pig
Human
Darwin’s Evidence
Geographic proximity of similar species – species on
different Galapagos Islands were similar to one
another, but different from those on mainland
Darwin’s Finches
DIVERGENT EVOLUTION
Adaptive Radiation
Darwin’s Evidence
Convergent Evolution
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Animals living on
different continents had
different ancestors;
however, because some
animals on each
continent lived under
similar ecological
conditions, they had
similar selection
pressures and thus
similar features
Placental Mammals
Australian Marsupials
Lamarck vs. Darwin
Remaining 19th Century Questions
Natural Selection
Special
Creation
The complexity and perfection of structures such as the human
eye indicates the work of a supernatural Designer.
William Paley
Natural selection results in better-adapted organs and
organisms, not perfect ones.
Charles Darwin
Remaining 19th Century Questions
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What about gaps in the fossil record?
What about these “great leaps” forward?
Is the Earth old enough for the slow process of natural
selection?
How did human mental and moral attributes evolve?
How does inheritance work?
Where do varieties come from?