Theory of Evolution, humans and primates

Darwin’s Theory of
Natural Selection
MAIN IDEA: Charles Darwin
developed a theory of evolution based
on natural selection.

Why was Darwin’s work
controversial?

Evolution vs. Creationism
 Creationism – belief that God
created all living things to be unique
 Evolution – theory that organisms
have changed over time.

Until the 1800s
 People thought the same types of
organisms on earth were always in
existence
 This changed when scientists found
fossils of organisms no longer on
earth

What made Darwin question
previous assumptions on how
different organisms came to be?

Scientists observed…
 Fossil evidence
 Many different species
 Variations (differences) within
species

Change in Thought
 Scientists began to wonder how and
why these changes took place
 2 biologists believed organisms
changed in response to their
environments:
 French Jean Baptiste Lamarck
 British Charles Darwin

Lamarck’s Theory
 1809 – Lamarck proposed his theory
of evolution
 Theory based on 2 hypotheses:
 Organisms develop traits by the use
and disuse of body parts
 Acquired characteristics – passed from
parents to offspring

According to Lamarck, why do
giraffes have long necks?

Lamarck’s giraffe example(Don’t
Copy)
 Lamarck assumed giraffes had short necks
originally and ate grass
 Grass died due to climate change
 Giraffes ate leaves off trees
 As giraffes stretched necks, necks grew
 Giraffe’s acquired long necks – passed to
future generations
 Scientists questioned this theory…

Charles Darwin
 Born in 1809
 Age 22, went on voyage on HMS Beagle
(British ship) as a naturalist
 Mapping expedition of S. America and
S. Pacific

Darwin’s Thoughts (Don’t Copy)
 Charles Lyell’s book influenced Darwin -
Lyell said Earth was millions of years old
 Observed fossils of marine animals on
mountains, etc
 Observed changing earth: earthquakes,
volcanoes, etc; saw change in the land
 Thought organisms would have to adapt to
these changes

Darwin’s Studies
 Observed thousands of different
species
 Took careful notes
 Collected specimens
 Studies fossils

Galapagos Islands (Don’t Copy)
 Off coast of Ecuador
 Observed MANY different species
 Many similar to those on coast of S.
America
 Observed tortoises, iguanas, finches, etc
with slight differences on different islands
 Ex: different beaks of finches

Help from Gould (Don’t Copy)
 John Gould, another British naturalist
 Concluded finches were different
species, and were not on mainland of S.
America
 Darwin though species changed after
reaching islands

DO NOW
 What is the difference between natural
selection and artificial selection?
 What is the difference between natural
selection and evolution?

Artificial vs. Natural Selection
 Artificial - breeding for desired traits
 Natural – naturally “desired” traits are
bred more often – causes gradual change
in species over time (evolution)

Darwin’s Theory
 Published book: On the Origin of Species
by Means of Natural Selection with help
from another scientist, Alfred Russel
Wallace
 Theory based on 4 main ideas:
 Variations
 Inheritance of traits
 Overproduction
 Survival of the fittest

Variations
 Variations (differences) occur among
members of the same species
 Ex: different breeds of dogs, horses, cats,
etc.
Inheritance of Variations
 Traits are inherited

Overproduction
 Organisms produce more organisms than
can survive and reproduce
 This ensures that some offspring will
survive to reproduce
 Ex: fish, insects, frogs, etc.

Survival of the Fittest
 Organisms with traits that are better for
adapting survive to reproduce
 Pass on these useful traits
 Natural selection – environment
determines which variations will be
selected

Peppered Moth Example
(DON’T COPY)
 Early 1800s, England
 Peppered moths were mostly light gray;
few were white, few were black
(variations)
 Gray blended with tree trunks – birds
didn’t see or eat them, so they survived,
but black ones were eaten

Peppered Moth Cont’d
(DON’T COPY)
 Industrial Revolution – many factories
built
 Black soot on trees
 Which moths were NOW more likely to
survive?

Do Now
 Once, many years ago, horses were the size
of cats. Now, they are obviously much
bigger. How would Lamarck explain this
change? How would Darwin explain it?

Evidence of Evolution
 Fossils
 Anatomy
 Embryos
 Molecules
 Biogeography

Fossil Evidence
 Show extinct species
 Show relationships between current and
ancient organisms
 Show intermediate species – those in
between ancient and modern species
 Difference in traits – derived vs.
ancestral

Anatomical Evidence
 Similar structures found in closely related
species; have common ancestor
 Diverse vertebrates have similar limb
structures, but may not have same function
–homologous
 Vestigial structures – structures not
currently used by organism; evidence of an
organism’s evolutionary past Ex: hind
limbs of dolphins/whales

Homologous vs. Analogous
 Remember, homologous – similar
STRUCTURE
 Analogous – structures with similar
FUNCTIONS, but different
structures/origins
 Ex: bat’s wing and bird’s wing -
analogous

Evidence in Embryos
 Pattern of meiosis (gametes)  fertilization
 mitosis (adults)
 All vertebrate embryos have homologous
structures that may not be in adults:
 Tails (most adults keep their tails!)
 Limb buds – become limbs
 Vertebrates have a common ancestor

Molecular Evidence
DNA:
 Basic genetic code for each species
 Ex: humans all have same basic genetic
code
 Species that are similar have many
similarities in their DNA
 Species with a more distant ancestor have
more differences in DNA

Molecular Evidence
Proteins:
 Because of similar DNA, organisms of
the same species have the same basic
proteins
 Similar species – similar amino acid
sequences in their proteins

Biogeography
 Study of distribution of organisms on
earth
 Similar environments lead to similar
adaptations in organisms, even if far
apart

Adaptations
 Traits that allow for survival
 Fitness – way to measure how effective
traits are
 Examples of adaptations:
 Camouflage
 Mimicry

Remember that…
 Not all traits evolve slowly; Ex: bacteria
 Not all traits increase fitness
 Mutations can be a source of new traits

Population
 Members of same species living in same
area
 All genes in a population = gene pool

Population Genetics
 Allele frequency – percent of certain alleles
(gene types) in a population’s gene pool
 Ex: all homozygous red flowers have a 100%
frequency for red alleles
 Usually remains stable in a population

Changes in the Gene Pool
 Changes can occur in the gene pool, which
could cause evolution
 Kinds or percentages of genes can change
 4 things cause these changes
 Natural selection
 Mutation
 Migration
 isolation

4 Factors Change the Gene Pool
1. Natural selection
 Well-adapted organisms survive to reproduce
 Pass on genes to next generation, increasing
the gene frequency

2. Mutation
• Adds a new gene to the gene pool
• Can cause small, immediate change, or go
undetected for generations
• Can be helpful, harmful, or neutral

3. Migration
• Movement of organisms into or out of a
population
• Causes gene flow – movement of genes in
or out of populations

4. Isolation
 Organisms become separate from other
organisms (geographic isolation)
 Caused by physical barriers, natural disasters,
etc
 Causes speciation
 Causes reproductive isolation between the
now separate species

Create
 With your group, pick any species, and
create a scenario as to how it may evolve
based on your assigned factor. Base your
predictions on facts about the species.
Describe and/or draw your predictions,
and then present to the class!

Gradualism
 Evolution through slow change
 Believed to be true by Darwin and many
other scientists
 Fossil evidence supports this

Punctuated Equilibrium
 Species remain unchanged for thousands
of years, then suddenly undergo rapid
changes
 Fossil evidence of trilobites – unchanged
for millions of years, then suddenly died
off

Theory of Evolution, humans and primates

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