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Evolution
T412
The Modern Synthesis 1932-1953
Restated Darwin’s ideas:
(1) Individuals in a population are variable for most traits, because
in every generation, mutation creates new genes; further,
sexual reproduction creates new gene combinations
(2) Individuals pass some of their genes to their offspring
Heredity
The Modern Synthesis 1932-1953
Restated Darwin’s ideas:
(1) Individuals in a population are variable for most traits, because
in every generation, mutation creates new genes; further,
sexual reproduction creates new gene combinations
(2) Individuals pass some of their genes to their offspring
(3) More offspring are produced than can survive
(4) Individuals that survive, or reproduce the most, have gene
combinations that best adapt them to their environment
i.e. adaptive radiation
Sexual Selection 1
male
Peacocks
Fiddler crabs
Males have traits important in mating displays (color, tail, claws)
whereas females lack such ornamentation
- male energy goes into looking good, attracting mates
- females invest energy in making large, healthy offspring
Sexual Selection 2
male
Peacocks
Fiddler crabs
Why do females chose fancy males?
If a male can survive predation and look that good while harbouring
parasites and resisting disease, he must have good GENES!!
Females want the best genes to combine with their own to give their
offspring the best chance of survival (i.e. natural selection).
Have a variety of offspring as environment is unpredictable (bet-hedging)
Natural selection 1
Darwin's finches
1977 - Drought
Mean beak depth
Drought favored deeper
beaks that could crack the
tough seeds that
were available
Directional selection
– not random
Natural selection 2
Peppered moths
• Before Industrial revolution, all moths were light
• As habitats became sooty, being light was
dangerous!
• Darker moths favoured, experimental and
genetic proof
• This did not happen in northern Scotland or
other rural areas
• Can still be seen today!
• Lighter moths re-appearing as pollution
reduced!
Phenotypic plasticity
Natural selection 3
Sickle Cell Anemia in humans
• Single point mutation
• SS, Ss, ss = genotypes
• African & Mediterranean groups
• Anopheles mosquito
• 150 bites per year
• 100% malaria infection rate in
kids
• 25% greater survivability from
malaria = Ss
Artificial selection
Darwin used examples of pigeon fanciers to
show how selection worked.
Other than a useful technique
• Experimental proof of natural and sexual
selection
• Used widely in farming, horticulture and
medicine
Summary
• Evolution is selection of favourable
inheritable genes that increase an
individuals ability to survive.
• Characteristics of the surviving individuals
are concentrated in future generations
causing changes in phenotype
• Selection can be natural, sexual or
artificial
Break
Evidence for Evolution
Evidence supporting the theory of evolution is found in:
(1) Similarities among related organisms
(2) Redundant/Unused structures
(3) Biogeography
(4) Fossil record (intermediate forms in a given families)
(5) Molecular evidence
Homologous Structures 1
same set of bones
constructs hands &
forearms in all
mammals,
indicating a
shared ancestry
Does it?
Homology in Embryological
evidence
Note that in the
first row all of the
embryos have a
similar number of
gill arches, which
are later destroyed
in all embryos
after the
salamander; note
in the second row
the similarity of
the spinal column
or all organisms.
Why should human
embryos develop
gill arches if not a
vestige of history?
Vestigial Structures 1
long predicted fossils of ancestral
whales with legs were recently
discovered
Vestigial Structures 2
Cavefish Eye Reduction
Vestigial Structures 2
Snake Hind-limbs
Biogeography 1
• The study of the global distribution of organisms
• Why are the faunas of Europe & North America
so similar, while those of Africa and South
America so dis-similar?
• Why is the fauna of Australia so different from all
other continents?
Biogeography 2
• Prediction: Groups that evolved after separation
of modern continents should be confined to
those continents, whereas lineages that evolved
before separation should be found on all
continents.
• Reptile-like primitive mammals are broadly
distributed over all continents (as fossils)
• carnivores & hoofed mammals, which evolved
later have never been found on Australia and
South America because they split off earlier.
The fossil series of
mammals arising
from reptiles is
remarkably
complete and
shows a gradual
evolution. Note the
gradation is cranial
morphology.
Amphibious fish!
Phylogeny of
modern fish
Reptiles to Birds
The Fossil Record 1
• Why is the fossil record not continuous?
– Fossilization is a rare event.
– Evolution isn’t always gradual.
– We do have quite a few complete and gradual
fossil series, i.e. modern horses (Eohippus to
Equus), mammals from reptiles, whales from
ungulate ancestors.
The Fossil Record 2
Where are all the
intermediate forms?
The Fossil Record 3
Where are all the
intermediate forms?
• They do exist!
• Often rare
• Limbs often lost
• Living fossils
The Fossil Record 4
Where are all the
intermediate forms?
Molecular Evidence
• Genetic clocks
• Genetic code similarities
• Homology in biological processes,
proteins, gene properties and possession
• Similar disease profiles and history
• Matches evidence from fossils and
preserved remains
Evidence for Evolution
Evidence supporting the theory of evolution is found in:
(1) Similarities among related organisms
(2) Redundant/Unused structures
(3) Biogeography
(4) Fossil record (intermediate forms in a given families)
(5) Molecular evidence
Break
Human evolution
Human evolution
• First change from other apes was
bipedalism — Australopithecus
anamensis
• Much debate on why
– Adaptation for cooling?
– Run faster?
– Carry things?
Early Hominids
• Australopithecines 4.2
-2.5 million years ago
– 3’7”, brain 400cm3
• Homo habilis
– 5’, brain 700cm3
• Homo erectus
– large, brain 1000cm3
Homo sapiens
•
•
•
•
Many ideas about human evolution
All recognize multiple species of Homo
All recognize origin in Africa
Questions about interbreeding of
different early groups
• Questions about which were direct
ancestors of modern humans
Theistic evolution
If we evolved where does God fit in?
Either……
• God created us separately from other hominids but so that it would look
like we had evolved, or
• Our physical bodies evolved from animal matter like everything else on
earth but the properties that make us human (i.e. the ability to control our
instinct, morality, our soul) were given to us when God deemed us ready,
i.e. the creation of humans, or
• God was not involved
Evidence against evolution 1
2nd law of thermodynamics: in a closed
system, things will move from an ordered to
unordered state (decay)
– The Earth is not in a closed system. New
energy from the sun is constantly flowing
in.
– Evolution doesn’t have to be a
“progression.” (eg. intestinal parasites)
Evidence against evolution 2
The Human Eye (and other complex structures)
• Within each taxonomic group variation in eye
structure occurs
• Increasing complexity can be seen within and
between families
• Some invertebrates have very complex eyes,
similar to mammals, i.e. squid, octopus
Evidence against evolution 3
Living cells
• Proteins and cells are easy
• Self-replication cant be replicated
• RNA + DNA not yet formed experimentally
Consciousness
• Very hard to define
• Some evidence of animal consciousness
• Speech + grammar can be genetically linked
YEC claims
• Why have the apes in WY stopped
evolving?
• RNA + DNA independently appeared?
• Drosophila experiments irrelevant!
• Cat + Dog don’t make “cog or dot”!
• Peacock’s tail too pretty
• Behaviour can’t evolve, i.e. Migration
• Speciation happens but not evolution