Download Natural Selection

Evolution
by
Natural Selection
Life’s Natural History is a Record of Succession & Extinction
In historical context
• Darwin did not originate the idea of evolution!!!
1. English naturalist who proposed the
theory of evolution by natural selection
1. Darwin sailed around the world on the
HMS Beagle and carefully studied
thousands of different plants and
animals
1. Most of animal species on
the Galápagos live
nowhere else in world, but
they resemble species
living on South American
mainland.
800 km west of mainland
1. Galápagos birds
a) 22 of the 29 species of birds
on the Galapagos are
endemic - found only on
these islands
2. One particular group…
a) at first, he paid little note to
a series of small but
distinctive birds
b) some were woodpeckerlike, some warbler-like, &
some finch-like
1. Darwin was amazed to find out they were all
finches
a) 14 species
b) but only one species on mainland of
South America - 800 km away
c) all presumably originated from mainland
Correlation of species to food source
Adaptive radiation - divergent evolution in which ancestral species evolve
into an array of species to fit a number of diverse habitats.
1. Differences in beaks
a) associated with eating different foods
b) adaptations to foods available on islands
2. Darwin’s conclusions
a) when original South American finches
reached islands, adapted to available food in
different environments
b) over many generations, the finches changed
anatomically & behaviorally
c) accumulation of favorable traits led to the
emergence of different species
1. Finches with beak
differences allowed
them to…
a) successfully feed
b) successfully compete
c) successfully
reproduce
d) pass successful traits
onto their offspring
1. Evolution is the gradual change in a species, or
populations over time, not individuals.
2. Darwin was the first scientist to realize that
evolution can work by natural selection.
a) Natural Selection – Is a mechanism for change
in populations. It occurs when organisms with
favorable variations survive, reproduce, and
pass their variations to the next generation
i. E.g. Thick fur is a favorable trait in cold
environments
• His theory was simple…
(1)Variation exists in natural populations
(2)Many more offspring are born each season
than can possibly survive to maturity
(3) As a result, there is a struggle for existence
(4)Characteristics beneficial in the struggle
for existence will tend to become more
common in the population, changing the
characteristics of a species
(5)Over time, and given a steady input of new variation into
a population, these processes lead to the emergence of
new species
1. Darwin referred to all of these factors together
as natural selection:
a) Variation
b) production of more offspring than can survive
c) Competition
i. for food, for mates & nesting spots, to
escape predators
d) differential survival based on traits
1. Evolution by natural selection happens in
populations, not individuals. A single
organism cannot evolve. Populations
evolve.
2. Populations evolve because there is
variation
3. Variation causes some organisms to be
better fit than others. Better fit organisms
are more likely to survive and pass their
genes to the next generation
• Peppered Moth
◆
dark vs. light variants
Peppered moth
Year
1848
1895
1995
% dark
5
98
19
% light
95
2
81
• Why did the population change?
◆
early 1800s = pre-industrial England
• low pollution
• lichen growing on trees = light colored bark
◆
late 1800s = industrial England
• factories = soot coated trees
• killed lichen = dark colored bark
◆
mid 1900s = pollution controls
• clean air laws
• return of lichen = light colored bark
◆
industrial melanism
1. Artificial Selection: Humans choose
individuals with certain traits for
breeding
2. After many generations of selection,
dramatic evolutionary changes can
result
i. Dogs
ii. Fruits/Vegetables
iii. Livestock
1. Adaptations
a) Structural
b) Mimicry
c) Camouflage
d) Physiological
2. Fossil Record
3. Comparative Anatomy
a) Homologous
b) Analogous
c) Vestigial
4. Embryological Development
5. DNA Similarities
1. All organisms have adaptations which
help them survive in their particular
environment
2. Adaptation: a structure or behavior that
helps an organism better survive in its
environment
Evolution of Mole Rats
1. Mimicry: a structural adaptation that
enables one species to resemble
another species
a) E.g. A harmless species might mimic a
poisonous one
1. Camouflage: a structural adaptation
that allows a species to blend in with its
surroundings
1. Many bacteria have evolved resistance to
antibiotics in the last 50 years
2. Pests have evolved resistance to pesticides
1. Insecticide & drug
resistance
a) insecticide didn’t kill
all individuals
b) resistant survivors
reproduce
c) resistance is
inherited
d) insecticide becomes
less & less effective
1. Fossil: Any trace of a dead organism
a) Fossils show the evolution of species
over the past millions of years
b) Fossil evidence proves that modern
species have evolved from ancient
species
Archaeopteryx
Puijila the walking seal
Tiktaalik
1. Homologous structures: Body
structures on different organisms that
are similar in structure (same bones)
and DID evolve from a common
ancestor
Homologous Structures
2. Analogous structures: Body structures
on different organisms that are similar
in function but DID NOT evolve from
the same ancestor (bird wing and
butterfly wing)
Moth (insect)
Pterodactyl (reptile)
Bird
Bat (mammal)
Analogous Wing Structures
3. Vestigial structure: body structure in an
organism that no longer serves its
original purpose but was useful to an
ancestor (useless wings on the African
ostrich)
1. Early in development, human embryos and
embryos of all other vertebrates are very
similar, which suggests that all vertebrates
are related
1. Nearly all organisms have DNA, ATP,
and many of the same enzymes
2. The DNA (genes) of closely related
organisms looks very similar