Population Change and Evolution

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Population Change and Evolution
Phylogeny

The history of
the evolution of
a group of
organisms

Adaptation – an inherited trait or set of traits
that improve the chances of survival and
reproduction of an organism

Evolution – the cumulative changes in
characteristics of a population in successive
generations
Theories of Evolution
Lamarck
1.
Law of Use and Disuse: organisms can
change their body features during their
lifetimes to satisfy their needs.
Theories of Evolution
Lamarck
2. Acquired characteristics are inherited:
Those characteristics changed during the
lifetime of an individual can be passed on to
offspring

Ex) Giraffes are able stretch their necks to
reach leaves and this trait is passed on to
their offspring.
Darwin


Job was a ‘naturalist’ – recorded and
sampled new species
Voyaged on the Beagle to the Galapagos
Islands
Darwin observed many species
Ex) Finches had adapted to eat blood, use
sticks in holes, drill holes
Darwin
He also noticed curious species:
 Iguanas that ate algae from ocean
 Flightless cormorants
Darwin

Assumed that all species evolved from a
common ancestor, probably from the
mainland

Ex) armadillo evolved from glyptodont
Darwin

proposed that evolution occurred by natural
selection and published his theory in 1859

Another scientist Alfred Wallace had similar
ideas
Theory of Natural Selection
1)
2)
Overproduction – more offspring produced
than survive
Struggle for existence – organisms
compete within and between species
Theory of Natural Selection
3) Variation – exists in any population and the
variations are passed on to the next
generation (genetic differences)
Theory of Natural Selection
4) Survival of the Fittest – surviving
organisms are ones better able to compete,
survive and reproduce. The others die
without leaving offspring (natural selection)
Theory of Natural Selection
5) Speciation – over numerous generations,
new species arise by accumulation of
inherited variations of traits; considered new
species when members cannot interbreed
with original species.
Key Concept

Those organisms that live long enough to
REPRODUCE will pass their DNA for the
‘desirable’ traits onto their offspring.

Those organisms less suited will die before
reproducing.

The population becomes more fit
Giraffes



Began with short necks
Those that were BORN with slightly longer
necks got more food
Could grow stronger to outrun predators, and
survived to have babies!
How do new traits appear?

Mutation

Sexual reproduction produces new
combinations
Peppered Moths


Were white with black spots ( a few were
darker)
Industrial revolution – soot on tree trunks
Peppered Moths
Peppered Moths


Within a few years, virtually all the moths
were black
Story may be simplified, but many other
examples exist
Ex. Fish becoming more oblong after net fishing
introduced in AB lakes
Microevolution


Is the changing of an organism (population of
organisms) over time without a change in
species
Eg. Antibiotic resistance
Macroevolution

Species differences
become so great
that they are no
longer able or no
longer interested in
interbreeding

Geographic isolation
often the cause
Macroevolution


Human evolution – most controversial subject
Evidence especially from Africa/Indonesia
Adaptations

Driven by natural selection

All help organisms to pass their genes to next
generation
Structural – structures that improve a
species ability to survive and reproduce
Ex. Modification of limbs in mammals
Ex. Camouflage
1.
Ex) warning colors
2.
Physiological – based on chemicals
Ex. pheromones – chemicals that influence the
behavior of other organisms (attract mate,
alarm)
Ex. venom production
3. Behavioral – behaviors
Ex. migration, hibernation, phototropism
Convergence


Very different species may also develop
similar adaptations due to similar needs in
their environment
Eg. Squid and human eye
Adaptive Radiation


Or divergence
Similar species become quite different due to
differing environmental needs
Two Versions of Evolution
Gradualism: species gain small changes with
time
Punctuated Equilibrium: new species born
suddenly with better adaptation
- This adaptation rapidly becomes the only one
in the population
Human Origins
Evidence For Evolution

Fossil record: organisms that once existed on
earth do not exist today (dinosaurs)
Evidence For Evolution
Radiocarbon dating – is controversial, but
useful for long-scale dating
Evidence for Evolution

Embryology– all embryos (from worms to
humans) go through very similar stages
Evidence for Evolution

Homologous structures have common origins in
the embryo (eg. Gill slits, forelimbs of
vertebrates)

Evidence of a common ancestor
Evidence For Evolution

Analogous structure: similar
structures, but develop from different
embryological structures

These organisms do NOT descend
from a common ancestor
Evidence For Evolution

Eg. Wings of insects, birds and bats
Evidence for Evolution
Vestigial Structures
Are structures present in organisms that
have no present day functions
 May be ‘left over’ from previous
evolutionary stages

Evidence for Evolution
Ex)
Pelvis and leg
bones in whales
Evidence for Evolution
Ex)
Limb buds and
claws in snakes
Human
Vestigial
Structures
Evidence for Evolution
Comparative Biochemistry

Recent advances in DNA profiling and
protein sequencing has allowed us to
study the similarities in common
molecules
Primate
Chimpanzee
No. Of Amino
Acids Different
From Humans
Identical
Gorilla
1
Gibbon
3
Rhesus Monkey
8
Squirrel Monkey
9
Evidence for Evolution

Biogeography – study of
geographical distribution of plants
and animals

Theory of Continental Drift – all
continents were once joined into one
supercontinent called “Pangaea”,
then broke apart and continue to
move apart today
Theories on Origin of Life



‘scientific’ theories
based on the “Big
Bang”
Explosive, outward
movement of mass,
continuing today
Nuclear fusion
causes elements to
form in stars
Origin of Life



On earth, a ‘primordial soup’ was
formed
Methane, ammonia, water
Urey and Miller – famous experiment –
caused organic compounds to form
when electricity (lightning) introduced to
these compounds

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