Download The Theory of Evolution

The Theory of
Evolution
Darwin and the development of
the theory
What is a SPECIES?

Group of similar organisms
– Structurally
– biochemically

Can interbreed successfully in nature
– Offspring are healthy
– Offspring are fertile (can reproduce)
These organisms are
not new species…Why?

Mule

Liger
Variation

Variation – differences between
individual members of a population

Members of a species are very
similar, but differences can be
observed, or not, make each
individual unique.

May be caused by mutations
Mutations

Changes in DNA base sequences

Most are either neutral or harmful

Those that allow the organism to
survive better in a particular
environment are good and are more
likely to be passed on to future
generations.
Most variations are not
caused by mutations

Sexual reproduction combines
genes from different parents

Crossing over during meiosis
can produce variations
Adaptation
An inherited trait that
increases the population’s
chances of survival and
reproduction in a particular
environment.
 Allows organisms to fit best
into a particular niche
(habitat and role)

Biodiversity



The variety and abundance of
species that makes up a biological
community.
Pine Barrens forests have little
biodiversity – a limited number of
species can survive there.
Tropical rain forests have great
biodiversity – many species in a
concentrated area.
Organisms have changed over
time to produce so many
different forms of life
Theories accepted
before Darwin

1769 – Bonnet – theorized that
fossils were from animals/plants
that lived before catastrophes
that made them extinct.
Jean Baptiste Lamarck
Use and disuse
 Inheritance of acquired
characteristics

Darwin and his theory

Charles Darwin lived
in early-mid 1800’s.

Went on voyage around the world
as the ship’s naturalist – collected
specimens of plants and animals
during the 5+year-journey.
Darwin’s Voyage
Galapagos Islands
Darwin’s route
Darwin Returned Home to Think!

These influenced his development of the
theory:
– Evidence that the 13 different species of
finches found in the Galapagos Islands
were the descendents of one species.
– HERE ARE JUST A
FEW BEAK TYPES:
Artificial selection – farm animals
and plants
– Population control – population
limited by resources and nature
controls it by killing off some
members during natural
disasters, illness (epidemics),
blights in plants, etc.
– Geologic evidence
of slow changes
Darwin’s Theory of Evolution
by Natural Selection
There is variation within a
population
Some variations are good (helpful)
Not all young produced in a
generation can survive
1.
2.
3.
–
–
–
This leads to a struggle for existence.
Survival of the fittest.
Those that survive and reproduce are
those with the good variations.
Evidence supporting
Evolution

Fossils – remains of plants or
animals that lived before – can
show structures
Homologous Structures –
similar in structure, but have
different functions
Vestigial Structures
Inherited
 But, reduced in size and often
not used.

– Examples
 Snake
legs (they’re so reduced in size
that they are not apparent).
 Human appendix –no function, except
can cause problems.
 Human coccyx – tail bone.
Analogous Structures

Similar in function, but very different in
structure – indicate organisms are not
closely related
Insect wings
Bat wing
Bird wing
Embryological Evidence

If organisms have similar embryos,
they are more closely related than
those with less similar embryos
Sea lamprEy
pond turtle
chicken
cat
human
Origin of Species

Speciation – evolution of one or
more species from a single
ancestor species. can be from:
– isolation – usually because of a
geographic barrier such as a
canyon, mountain, or island
Divergent Evolution

Isolated populations of a species
evolve independently of each other.
– Ex – polar bears and brown bears
Convergent Evolution

Natural Selection produces
analagous (similar)
adaptations in different
organisms in response to
similar environments:
– African Serval cat & south american maned wolf
– See text p 242
– These animals have similar ears, legs, acute
hearing, habitat, and Occupy similar niches
Coevolution

Species that interact closely
often adapt to one another:
Adaptive Radiation

Many different species evolve from
one ancestral species – each new
species has a different niche
Evolution Observed:
Peppered Moths
Less pollution
More pollution
Light moths
Dark moths
Light tree
Dark tree
The End