Transcript Evolution by Natural Selection

Evolution
The Unifying Theory of Zoology
Contemporary Scientific History of the Universe
13.7 billion years in 30 volumes
-each volume = 450 pages
-each page = 1 million years
Big Bang, p. 1
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Origin of Earth
Life Begins
Complex Animal Life
Modern Humans
Dinosaurs
p. 450,
pp. 215-385
last sentence
What is Evolution?
Evolution = Descent with Modification
• Species originate as modified descendants of
other species.
• Biological evolution is the origin of new species
from previously existing ones over time.
“As many more individuals of each
species are born than can possibly
survive, and as consequently there
is a frequently recurring struggle for
existence, it follows that any being, if
it vary in any manner profitable to
itself, under the complex and
sometimes varying conditions of life,
will have a better chance of survival
and thus be naturally selected. From
the strong principle of inheritance,
any selected variety will tend to
propagate its new and modified
form.”
Charles Darwin,
The Origin of Species
Darwin’s Theory
• If there is a struggle for existence…
• If heritable variations exist among
members of a population…
• If these variations affect survival and/or
reproduction…
• Then species will change over time.
There is a struggle for existence.
• Species tend to produce more offspring
than the environment can support.
Darwin calculated that even
one slow-breeding female
elephant could give rise to
19,000,000 elephants after
750 years if all of her young
survived and reproduced at
the same rate. Obviously, the
environment cannot support
all elephants that are born.
Heritable variations exist.
• An impressive amount of variation exists
within living species.
Breeders of animals and plants use these diverse characteristics
to establish new varieties of dogs, cats, pigeons, wheat, cotton,
corn, and other domesticated organisms.
Variations affect survival & reproduction.
• Certain individuals
possess inherited traits
that make them more
likely than other
individuals to survive
and/or reproduce.
• “Differential survival and
reproduction”
Bears
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Colored for their arctic environment
Excellent swimmer
Carnivore
Poor climber
High endurance
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Colored for their terrestrial environment
Poor swimmer
Herbivore
Excellent climber
Low endurance
Species will change over time.
Evolution in Action
Populations evolve, not individuals.
• Individuals may change throughout their
lifetimes, but this is not evolution.
• Evolution occurs across many generations.
• Over time, populations acquire new
characteristics that enhance their ability to
survive and/or reproduce in a given
environment.
Variations are “Random”
• Mutation and sexual
recombination occur
randomly.
• The variations that occur
do not anticipate the
“needs” of the organism.
• In this sense, “random”
does not mean that
anything can happen.
Natural Selection is NOT Random
• Genetic variation occurs randomly, but
natural selection is NOT random.
• Genetic variations that aid survival and
reproduction are more likely to become
common than variations that do not.
Nature imposes a direction to
evolutionary development.
Though dolphins are more
closely related to humans than
they are to sharks, they have
evolved bodies adapted to an
aquatic environment.
Evolution is About Consequences
• Evolution is historically
contingent; that is, “windows of
opportunity” constantly open
and close.
• Once certain changes have
occurred, the range of possible
future changes is permanently
altered.
“Windows of Opportunity”
The earliest turtles could not
retract their necks.
Later, two distinct forms of
neck retraction evolved.
Proganochelys
220 million years ago
side neck turtles
vertical neck turtles
(southern hemisphere) (northern hemisphere)
With the extinction of the turtles that could not
retract their necks, the possibility that another form
of neck retraction would evolve was lost.
Evolution is Predictive
Tiktaalik roseae
Ichthyostega
365 million years ago
Acanthostega
Tiktaalik
Panderichthys
Eusthenopteron
?
385 million years ago
Conclusion
“Nothing in Biology makes sense
except in the light of evolution.”
Theodosius Dobzhansky
(1900-1975)
EVOLUTION and ECOLOGY
The Big Picture – Putting the
Pieces Together
Biomes
• Many biomes in the earth:
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Grassland
Tundra
Taiga
Rainforest
Deciduous Forest
• Through evolution, animals adapt to live in
different biomes or ecosystems.
Populations
• A population is a group of organisms in a
species.
• A community is a group of populations
living in an ecosystem.
• Ecosystems vary based on biotic (living)
and abiotic (nonliving) factors.
Populations
• Animals in a population will have competition
for resources.
– Food
– Shelter
– Water
– Space
– Mates
Limiting Factors
• When resources are limited,
competition gets more intense.
• Limiting factors are a form of
environmental resistance that
limits population size.
Is limited population a good thing?
Biodiversity
• More populations living in
an ecosystem causes
BIODIVERSITY.
• Biodiversity means more
genetic variation =
increased likeliness for
new species to develop
• Certain biomes allow for
more diversity than others:
– Rainforest
– Coral Reef
Biodiversity
• Biodiversity drives
EVOLUTION
• Biologists most often
define biodiversity as the
"totality of genes,
species, and ecosystems
of a region".
– species diversity
– ecosystem diversity
– genetic diversity
Natural Selection
• With more variation, some animals will be better fit
for their environment than others.
• Survival of the fittest
• This causes “natural selection”
– gradual, non-random process by which biological
traits become either more or less common in
a population as a function of reproduction from their
bearers
Natural Selection
Same species = may have better fitness in different ecosystems
• The environment (nature) will change, and the
animal that will adapt best to those changes will
be the one that survives and reproduces.
Loss of Biodiversity
• Rapid environmental changes typically cause mass
extinctions.
– Human impact is now a contributor
• One estimate is that less than 1% of the species that have
existed on Earth are extinct.
• Extinction – the death of a species
– those genes are now absent from the gene pool
Symbiosis
• Animals are dependent on others in their
community. They all are “pieces” in the giant
“puzzle” that is an ecosystem.
• As animals evolve in their specific environments,
complex relationships form between species.
• We call this SYMBIOSIS.
Symbiosis
• There are 4 types of
symbiotic
relationships.
– Predator/Prey
Relationships: The
hunters and the
hunted.
Symbiosis
– Mutualism: relationship where both species
benefit (+/+)
Symbiosis
– Commensalism: relationship where one
species benefits (+/0)
Symbiosis
– Parasitism: relationship where one species
benefits and the other is harmed (+/-)