Download Natural Selection

Natural Selection
The Mechanism of
Evolution
Variation and Adaptation
 Species
consists of organisms that
can produce healthy fertile offspring.
 Variation
is defined as the
differences between individual
members of a population. The
unique attributes of each organism.
Variations w/in a Population
 Variations
are the things that make
organisms different from one another
 For
Homo sapiens variation could
be…….?
 Hair
Color
 Height
 Eye color

Inuit (Eskimos) have a stocky build. Less
surface area to volume to conserve heat.

Ethiopians: tall and skinny more surface area to
volume (this allows for cooling of the body).

Both are of the species Homo sapiens, but they
are different variations of the species.

They have evolved to suit their habitat
Sources of Variation
 Mutation
 Beneficial
- organism more likely to survive
and reproduce
 Deleterious - organism more likely to die
before reproduction
 Recombination
 Fusion
of gametes
 Meiosis
 Crossing over
Adaptation

An adaptation is an inherited trait that increases
a population’s chances of survival and
reproduction in a particular environment.
Ability to make tools
 The toxic slime of the Rough Skin Newt
 The Anteaters tongue and snout

Theories of Change

Charles Darwin
random generational variation with environmental
pressure over time causes change


Bonnot
theorized that periodically all life was destroyed by
natural disasters.
Lamarck
1. organisms strive to improve
2. use it or lose it
3. modifications are inherited
Natural Selection
Proposed by Charles Darwin:
1. There is variation within the population.
2. Some variations are good.
3. Not all offspring survive.
4. The individuals that survive and reproduce
are those with GOOD variations.
Factors Influencing Darwin
1.
2.
3.
4.
Charles Lyell - who believed the earth changed
slowly and uniformly
Animal breeding practices – how we have bred
animals for generations to get the traits that we
want.
Thomas Malthus - who studied human populations
and the factors that influenced them
Alfred Wallace - who independently reached the
same conclusions as Darwin
Natural Selection Says
 According
to Natural Selection, the most
successful individuals are those that
grow up to have offspring that grow up
to have offspring. Natural Selection is
more of a measure of reproductive
success and who leaves the greatest
genetic contribution to the population.
Fitness
 What
is “Survival of the fittest”?
 The
fittest individual grows up to have
the most offspring that grow up to have
offspring.
 Fitness
is a measure of reproductive
success.
Punctuated Equilibrium & Gradualism

Gradualism – small genetic changes act to change
populations slowly over time. Eventually two new
populations form.

Punctuated Equilibrium – populations remain
genetically stable for long periods, which are
punctuated by periods of rapid genetic change
(Adaptive Radiation)

Fossil evidence provides more support of the
theory of punctuated equilibrium than it does for
gradualism.
Evidence Punctuated Equilibrium
1.
Fossil record
2.
Comparative anatomical structures
3.
Comparative Embryology –
comparing the embryos of species
(ontogeny reflects phylogeny)
4.
Genetic or molecular evidence –
comparing the DNA of species
Comparative Structures

Homologous structures are “body parts” that
are common in different species because
they share a common ancestor. Whale fin /
human arm are examples.

Analogous structures are “body parts” that
serve the same function but are very different
in structure. Insect wings, bat wings and bird
wings.
Comparative Structures

Vestigial structures: Seemingly purposeless
structures like the appendix or tail-bone of
humans. The number of identified vestigial
structures have declined over the last several
years because there purpose has been found.
Speciation

A process development that creates more
than one species from a common ancestor.
Only one known widely accepted example.


The crocodile and the bird, both:
1.
2.
3.
4.
build nests
imprinting exhibited by young
sound the same when first born
scale tissue same as tissue that develops
feathers
Mechanisms of Speciation

Divergent evolution – isolated populations
evolve independently of one another.
Typically some geographic barrier arises
separating or dividing a population.

Adaptive radiation – a founding species
moves to an area with no competition, ie.,
the original founding finch in the Galapagos
Islands, and adapts to the various niches
within that ecosystem.
Evolution is the theory that
variation with natural selection
optimally adapts an population to
an environment. Environments
can change though. Sometimes
too quickly for evolution.