Transcript Evolutionary Thought

Evolutionary Thought
Theories of Evolution
Questions about the world that
started to set the stage for modern
evolutionary thought
 GEOLOGY
 Age of earth?
 Changing earth?
 POPULATIONS
 Competition?
 Change over time?
 Extinction of species?
GEOLOGY
Hutton and Lyell (geologists)
 James Hutton (1785)
 hypothesized earth to be very old when he examined
geologic features such as rock layers and erosion
 Charles Lyell (1833)
 Hypothesized that complex geologic processes like
erosion, volcanoes, etc. shaped the earth as we
currently see it.
 CONCLUSIONS:
 EARTH IS VERY VERY OLD!
 Today’s best guess???  4.6 Billion Years
1809:Lamarck’s Theory
 Use and Disuse:
 Body parts that are used more
grow stronger and bigger.
 Body parts not used will
deteriorate.
 Inheritance of Acquired Characteristics:
 Physical changes that occur in an
organism are inherited by its
offspring.
 Example: Giraffe’s neck gets
longer as it stretches to reach
food in trees.
 But was Lamarck correct?
 NO
According to genetics…
 only variations that occur in
gametes
the genes of ____________
are passed to offspring.
 variations that occur in
somatic cells (body cells)
_____________
are NOT inherited.
Thomas Malthus (1798)
 Observed human population
growth will eventually hit a limit
due to living space and available
food. Darwin would later apply this
to all organisms where these limits
result in competition.
 While Lamarck's reasoning behind
why change happened was
flawed, Lamarck and Malthus both
greatly influenced the thinking of
Mr. Charles Darwin.
Charles Darwin
 English scientist born in 1809
 1831 famous voyage around world on HMS
Beagle where he examined numerous
different types of animals and the wide
diversity of life he found
 Noted that organisms seemed to be
uniquely adapted to their environments
 Galapagos  Similar organisms on different
islands had unique characteristics that
suited their specific habitat
On the Origin of Species
 Published 1859
 Summarized his ideas on causes of
speciation
 Darwin's On the Origin of Species by
Means of Natural Selection, made several
points that had major impact on
nineteenth-century thought:
Main Principles of NATURAL
SELECTION
I. Competition.
II. Survival of the fittest
III. Descent with modification
Natural Selection: Competition
Members of the same species are
in competition with each other for
food and space.
 Over production:
 In a population, more offspring are
produced than can survive.
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“Struggle for existence”
 Individuals with traits that give them an
advantage make better competitors.
Natural Selection: Survival of the
Fittest
 Variation:
 There is variation within a
population and variations are
inherited.
 Adaptation:
 Traits that are favorable and
improve the organism’s ability to
function and reproduce.
 Survivors pass on their
variations. Therefore a larger
proportion in the next generation
will have those variations.
 “Fitness” in evolution is a
measure of an individual’s ability
to survive and pass on genes
(reproduce!)
measure of an individual’s genetic
contribution to the next generation.
Natural Selection: Descent with
Modification
 As new desirable characteristics become
established within a population, the
species as a whole changes over long
periods of time.
 Evolution is the development of new
organisms from preexisting organisms
over time.
 Speciation:
 Over time, small changes
accumulate and populations
change.
 Species: a group of organisms that
can mate and produce fertile
offspring.
 Sometimes, two populations diverge
(change differently) and become two
separate species.
 Each of the Hawaiian honeycreeper species has a
bill specialized for eating certain foods. Scientists
suggest that all 23 honeycreeper species
apparently arose from a single species that
migrated to Hawaii.
Lamarck vs Darwin
Lamarck
Use / disuse
Transmission
of acquired
characteristics
Darwin
Variation
Inheritance
Increasing
complexity
Differential
survival
No extinction
Extinction
Principle of Common Descent
 All species (living and extinct) have evolved from
common ancestors for a very long time.
Evidence of Evolution
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Fossil Record
Geographic Distribution
Transitional Species
Comparative Anatomy
Vestigial Organs
Comparative Embryology
Comparative Biochemistry
Fossil Record
 Preserved remain of ancient
life in rock support change
over time.
 Fossils found in lower levels
of rock older than ones
above. (relative age)
 Majority of species (over
99%) that have existed on
this planet are extinct!
 Very hard for an organism
to become a fossil.
How is the age of fossils and rocks
determined?
 Radiometric dating – using half-lives of
radioactive isotopes
 Radioactive isotopes decay at a constant rate
 Half Life  length of time for ½ of an isotope
to decay
 Ex. Carbon-14 decays to Nitrogen-14
 Half-life = 5,730 years
 Carbon 14 can only be uses to date fossils
less than 50,000 years old!
Geographic Distribution
 Biogeography
 study of the distribution of plants and
animals throughout the world
 Some fossils found on different continents
nearly identical supporting movement of
continents.
 There are patterns in how species occur
geographically, based on such factors as
where they evolved, how far they
dispersed, and how changes in the Earth
affected their distribution.
Transitional Species
 While theoretically, all species are
“transitional”, we use this term to classify
certain species as almost “stepping
stones” from one type of organism to
another.
Ex.
Fish Amphibian
Homologous Structures
(Comparative Anatomy)
 Scientists note
similarities among
physiology of
organisms
 Morphologically
similar structures
that perform
different functions
are called
homologous
structures.
Analogous Structures
 Serve similar function but have a much
different structure
 Ex. Insect wing and bird wing
 Ex. Squid eye and human eye
 Ex. Whale fin and fish fin
Vestigial Organs
 Rudimentary structures that are of marginal
or no use to an organism, or structures in
which the shared form appears to be
inefficient.
 Examples
 Skeletons of some snakes retain the vestiges of
pelvic girdle and leg bones of walking
ancestors.
 Some blind, cave-dwelling fish have eyesockets but no eyes.
Comparative Embryology
 closely related organisms go
through similar stages during their
embryonic development
Biochemical Similarities
 What we all use
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DNA
ATP (energy molecule)
similar enzymes,
same codons for protein synthesis
same 20 amino acids etc.
 Remember, at the cell level we are very
close to most other eukaryotic organisms!
Evolution in Action
 All inheritable physical traits that appear in an
organisms can be looked at as changes in an
organism’s genetics
 Darwin did not understand genetics and therefore
could not explain how traits were passed down
through generations.
 We now can apply our understanding of genetics
and apply them to evolutionary theory.
Phylogeny
 the connections between all groups of
organisms as understood by
ancestor/descendant relationships.
 Express relationships using a
CLADOGRAM
Cladogram
 Gene Pool is combined genetic information of
all the members of a particular population
 In a given gene pool, there will typically be two
or more different alleles for a given gene.
 Relative Frequency – number of times that
an allele occurs in a gene pool compared with
the number of times other alleles occur.
 We can oftentimes see that different alleles
have different frequencies in different parts of
the world. Why do you think this is so?
Ex. Frequency of B allele for blood type
Genetic Change basis of Evolution
 Natural selection acts on phenotypes
NOT genotypes, however, this process
determines the relative frequencies of
alleles.
 Ex. Sickle cell anemia
 Phenotype (blood cell shape)  because
heterozygous individuals are resistant to
malaria.
 Malaria resistance causes sickle-cell allele to
be selected for in the population.
Mechanisms of Evolution
 Introduce new Alleles
 Sources of Genetic Variation
 Mutations
 Sexual Reproduction
 External factors affect the allele
frequency
 Remember, it is mutation that proposes
and selection that disposes
What can change allele frequencies
besides natural selection?
 Genetic Drift
 Evolutionary Change can also happen without
natural selection
 In large populations, the laws of probability
help predict allele frequencies.
 In smaller populations random change in
allele frequency (genetic drift) may occur.
 Chance occurrences may increase/decrease
frequency of alleles
Mass Extinctions
 There have at least 5 mass extinctions.
 Permian – 250 mya, over 90% of marine and
terrestrial species disappeared; maybe due
to volcanoes, Pangeae, glaciation
 Cretaceous – 65 mya; ½ marine and many
terrestrial forms, including dinosaurs; due to
environmental changes or asteroids hitting
the earth
Genetic Equilibrium
 In order for there to be no evolution (allele
frequencies remain constant) five
conditions must be met;
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Random mating
Large population
No migration in or out of population
No mutations
No natural selection
 Is this ever the case?
TWEEKING DARWINISM
 Traditionally, it was believed that evolution
happened in small steps over long period
of time. This is called gradualism
 More recently, scientists like Stephen Gould,
proposed the idea of punctuated equilibrium
which is that a species may remain relatively
stable with sudden periods of rapid evolution
due to some environmental factor.
 CHANGES IN SPURTS!
What is a theory?
 Evolution is an observable fact (bird beak
size changing, antibiotic resistance in
bacteria, etc.) but the term theory allows it
to grow and develop.
Misconceptions About
Evolution