Download Mechanisms of Evolution

MECHANISMS OF
EVOLUTION
TARGET #3- I CAN EXPLAIN HOW
VARIATION CONTRIBUTES TO AN
ORGANISM’S SURVIVAL
After studying Malthus, Darwin realized that if
more individuals are produced than can survive,
members of a population must compete to
obtain food, living space, and other limited
necessities
 Described as the “struggle for existence”
 Variation plays a vital
role in the struggle for
existence
 Individuals have natural
variations among their
heritable traits
 Darwin hypothesized that
some of these variations
are better suited to life in
their environment than
others
 Ex: a lion with longer claws
and higher endurance is a
better hunter than a lion
without those traits
Includes
 Body parts
 Claws
 Wings
 Coloration
 Bright colors
 Camouflage
 Mimicry
 Physiological functions
 Photosynthesis
 Brain capacity
TARGET #4- I
CAN DESCRIBE
AN ADAPTATION
Adaptation: any heritable
characteristic that increases an
organism’s ability to survive
and reproduce in its
environment.
TA RGET #5 - I CAN EX PL A IN W H Y O RGA NISMS W I T H
G R EATER FITN ES S G EN ER ALLY L EAV E M O R E
O FFS PR ING TH AN O RGA NISMS T H AT A R E L ES S FI T
Darwin recognized that there must be a
connection between the way an organism
“makes a living” and the environment.
Differences in adaptations affect an organism’s fitness
 Fitness: how well an organism can survive and reproduce in
relation to others of the same species within it’s environment
 Individuals with adaptations that are well suited to their environment can
survive and reproduce more offspring
 Individuals with characteristics that are not well suited to their
environment either die without reproducing or leave few offspring
 The difference in rates of survival and reproduction is called
“survival of the fittest”
Natural Selection
 The process by which
organisms with
variations most suited
to their local
environment survive
and leave more
offspring
 The environment
influences fitness
Does not make the organism “better”
Does not move in a fixed direction
A process that enables species to
survive and reproduce in a local
environment
 If local conditions change, some traits may
become adaptive
 If conditions change faster than a species
can adapt, the species may become extinct
TARGET #6- I CAN SUMMARIZE
HOW NATURAL SELECTION
ALLOWS ORGANISMS WHICH ARE
MORE ADAPTED SURVIVE IN
THEIR ENVIRONMENT
Natural selection occurs in any
situation in which more individuals
are born than can survive, there is
a natural heritable variation, and
there is variable fitness among
individuals
TARGET #7- I CAN EXPL AIN HOW A
POPUL ATION OF ORGANISMS IN A SPECIES
UNDERGOES NATURAL SELECTION
Adaptations and variations among individuals in
populations of species does not begin in the
environment
 Step 1: a mutation occurs within the DNA of an
organism
 Step 2: that mutation leads to the production of a
protein that either does not function, over functions, or
has a different function than originally intended
 Step 3: the mutation is passed down to an offspring
where it is expressed in the offspring’s phenotype
Step 4: the mutated phenotype is naturally
selected by the environment as being more
advantageous, and that individual has more
offspring than the non-mutated individuals
Step 5: the mutation is passed down, generation
to generation, until the population of organisms
in that species retain that mutation
**Step 6: if enough mutations collect within a
population of individuals in a given species, then
a new species is formed
EXAMPLE- THE SPIRIT BEAR
 Within the species black bear (Ursus americanus), there
is a subspecies (Ursus americanus kermodei)
 There are about 400 individuals in this subspecies
 About 10% of this subspecies is homozygous recessive for a
mutation that turns their coats whitish
 Caused by a mutation in a pigment gene, known as MC1R (Melanocortin
receptor)
 MC1R is involved with the synthesis of the pigment eumelanin
 A mutation in this gene in humans results in red hair)
 Evolutionary Advantage
 Better at catching fish during the day than their dark bear counterparts
 Are considered sacred by the local people, the Tsimshian, so they are
hunted less
Lineage can be traced back over many
generations
Over many generations, adaptation
could successfully lead to the
evolution of new species
 Darwin proposed that living species are
descended with modification from
common ancestors
 Known as descent with modification
TARGET #8- I CAN EXPLAIN
WHAT DARWIN’S MECHANISM
FOR EVOLUTION SUGGESTS
ABOUT LIVING AND EXTINCT
SPECIES
Natural selection depends on the
ability of organisms to reproduce,
or to leave descendants
Means that life as been on earth
for a long time
Basis for the explanation of the
diversity of life
According to the principle of
common descent, all species,
living and extinct, are
descended from ancient
common ancestors