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The Evolution of Animal Traits
Chapters 15 and 16
EVOLUTION
 The theory of evolution can explain the
diversity of life on Earth.
 Evolution, otherwise known as change over
time, is the process by which modern
organisms have descended from ancient
organisms.
Mimicry
 Type of evolution when one organism
comes to resemble, or mimic, another
organism over time.
Viceroy
Monarch
Convergent Evolution
 Convergent evolution occurs when 2
groups of unrelated species adapt to the
same kind of environment.
 Example: sharks (fish-like), dolphins (mammals)
Theories of Evolution
 Many important theories about animals and
animal adaptations were developed hundreds
of years ago.
 We will discuss a few of these and the
scientists/professionals that developed them,
like Darwin, Lamarck and Malthus.
Charles Darwin
 Charles Darwin
contributed more than
any other scientist to our
current understanding of
evolution.
 He gave us the Theory
of Natural Selection.
Charles Darwin
On many trips abroad,
Darwin observed a
tremendous diversity of
organisms and noticed
that many plants and
animals were very well
suited to their
environment.
Charles Darwin
On the Galapagos Islands,
he noted that though the
islands were close
together, they had very
different climates and thus
the physical appearance of
similar organisms (like
birds) varied from island
to island.
Darwin’s finches
Charles Darwin
 Darwin collected many fossils from ancient
organisms and wondered why the species
represented by the fossils no longer existed.
 Knowing that the Earth could change over
time, Darwin realized that life might as well.
Jean Baptiste Lamarck
 French scientist who was one of the
first scientists to recognize that
evolution had occurred and that
organisms had to adapt to their
environment in order to survive
 He said that body changes that an
organism develops over time could
be passed on to their offspring
 Ex. Giraffes developed long necks
to reach food
Jean Baptiste Lamarck
 Lamarck hypothesized that an organism
could gain or lose traits during its lifetime
by using or not using organs
 These changes could be passed on to their
offspring and eventually change the
whole species over time.
Thomas Malthus
 Malthus was an economist that
hypothesized that if a population
continued to grow unchecked, it
would run out of living space and
food.
NATURAL SELECTION
 Darwin’s Theory of Natural
Selection states that individuals
differ and that some of these
differences can be passed on to
their offspring.
More offspring are produced than
can survive & reproduce in a given
area, so there is competition for
limited resources like food, mates
and territory.
NATURAL SELECTION
NATURAL SELECTION
 Individuals that are best suited to their
environment are able to survive and
reproduce (therefore passing on their genes)
most successfully so that it creates a
“survival of the fittest”.
 Fitness is the ability to survive and reproduce
in a specific environment and results from
making adaptations to the environment, thus
causing a species to change over time.
Adaptation
 The changing of a
species that results
in its being better
suited to its
environment and
thus more
successful in living
and reproducing.
NATURAL SELECTION
 Darwin argued that
species alive today all
descended from a
common ancestor, but
each made its’ own
adaptations according to
their environment.
Darwin’s Evidence that
Supports Evolution
 1. FOSSILS –
Scientists can
compare fossils
from older &
younger rock
layers
Darwin’s Evidence that
Supports Evolution
 2. GEOGRAPHIC
DISTRIBUTION OF
LIVING SPECIES –
the presence of
similar but unrelated
organisms in similar
environments.
Darwin’s Evidence that
Supports Evolution
 3. HOMOLOGOUS
STRUCTURES – body
parts that develop from the
same type of embryonic
tissue, but have different
mature forms in different
animals.
 They provide evidence that
organisms descended from
a common ancestor.
Darwin’s Evidence that
Supports Evolution
 4. SIMILARITIES IN
EARLY
DEVELOPMENT – The
embryonic stages of
many animals are very
similar, which also
provides evidence that
animals share common
ancestors.
Genetic Variation
 A population is defined as a group of
individuals of the same species that interbreed.
 Members of a population share common genes
called a gene pool.
 Genetic variation occurs when genes either
mutate or are shuffled, which both increase the
different genetic combinations possible within a
species.
Speciation
 Speciation is the formation of new species.
 For one species to evolve into two new
species, the gene pools of the two
populations must become reproductively
isolated, which means they can no longer
interbreed and produce fertile offspring.
 Reproductive isolation can be 1 of 3 types:
Types of Speciation
 BEHAVIORAL ISOLATION: Occurs when
populations have different courtship rituals.
 GEOGRAPHIC ISOLATION: Occurs when
populations get separated by physical barriers
such as mountains or rivers. (Ex. Grand Canyon)
 TEMPORAL ISOLATION: Occurs when
populations reproduce at different times of the
year. (Ex. Different breeding times in animals or
different times when flowers bloom.)
History of Life
 The first known life forms evolved about
3.5 billion years ago & resemble modernday bacteria.
 The first eukaryotes evolved about 2
billion years ago.
FOSSILS
 Fossils tell us a great deal
about the past.
 They are essentially preserved traces (like
footprints or burrows) or remains (like bone,
teeth and shells) of ancient life that once
existed on Earth.
FOSSILS
 We can use fossils to infer what life on Earth
used to be like once upon a time.
 Scientists often use dating methods to
determine the age of fossils.
FOSSILS
 Radioactive elements in fossils
decay at a steady rate over
time, which is known as halflife.
 A half-life is the length of time
needed for half of the
radioactive atoms in a fossil to
decay.
 By finding this, we can
determine the full age of a
fossil.
EVOLUTION
 Remember, an organism’s ability to survive
and reproduce makes it successful, which
happens only if it can adapt to its’
environment, eventually leading to an overall
change (evolution) in the species over time.
 In other words, if it doesn’t change
it won’t survive!!
You’ll be quizzed over these
notes next class!