The Process of Evolution
Darwin’s Theory of Evolution
• The theory of
evolution explains
how a species or type
of organism changes
over time.
• The theory of
evolution was first
proposed by the
English scientist
Charles Darwin.
Darwin’s Theory of Evolution
• Darwin traveled on H.M.S.
Beagle to a group of isolated
islands off the coast of South
America called the Galapagos
Islands.
• His studies in the Galapagos
Islands lead to his publishing
the book On the Origin of
Species. It was in this text that
Darwin first presented his
ideas on evolution.
Darwin’s Theory of Evolution
• Darwin studied a
group of birds called
finches while on the
islands. He noted
that some species of
finches were very
different from each
other in the shapes of
their beaks.
Darwin’s Theory of Evolution
• Darwin suggested that these species of finches shared a
common ancestor and that, over time, each species’
had adapted beaks suitable to the type of food that was
available on their particular island.
Darwin’s Theory of Evolution
How does evolution occur?
A Struggle for Existence
• Though a plant may produce hundreds of seeds, only a
few of those seeds will grow into mature plants.
• In fact only a relatively small number of offspring of any
species survive to produce their own offspring…why?
A Struggle for Existence
• Organisms must compete for
limited resources such as
food and shelter.
• Organisms must cope with
predators, animals that feed
on other animals and
parasites, organisms that live
on or within another organism.
• Organisms must be able to
handle extremes of climate
such as heat and cold.
Genetic Variation
• You may have your “mother’s
ears” or your “grandfather’s
eyes”.
• By way of reproduction,
characteristics are passed on
from parents to offspring.
• The resulting offspring
resemble their parents and
each other, however; they
show some differences.
• The differences among
offspring are called genetic
variations.
Genetic Variation
Genetic variation can
occur in either one or
two ways.
• The traits of the offspring
are the result of a new
assortment of traits
inherited from both
parents.
• Mutations, or sudden
changes may occur in the
genetic material of an
organism.
Genetic Variation
Types of Genetic Variation
• Structural or anatomical:
differences in the body of an
organism (muscle size or
thickness of fur).
• Physiological: differences in
the functioning of the organism
(resistance to disease,
digestion).
• Behavioral: differences in how
an organism reacts (mating
display, feeding time).
Genetic Variation
Types of Genetic Variation
• Chromosomal and genetic:
differences in the arrangement
of genetic information along
the chromosomes.
• Molecular: differences in
molecules that make up an
organism and allow it to
function (enzymes).
Summary …
• There is a struggle for existence, which limits the number of
survivors.
• There are differences among offspring due to individual variations.
That being the case …. What decides which individuals survive to
reproduce and become parents of the next generation?
Natural Selection
• Special characteristics
that make an organism
well suited to a particular
environment are called
adaptations.
• Whatever slight variations
an organism has that
gives it an advantage
over other organisms
would make it more likely
to survive and pass on its
genetic variations to
future offspring.
Natural Selection
• The process, whereby
conditions of life
determine which
organisms have survival
advantages and are more
likely to reproduce is
called natural selection.
• The gray moth in this
picture is more likely than
the black moth to survive
and reproduce.
Artificial Selection
• The selection by
humans of organisms
with specific, desired
characteristics is
known as artificial
selection.
Antibiotic Resistant Bacteria
Evidence for Evolution
Creating a Family Tree
• Biologists try and understand
the relationships that exist
among different species.
• Simple diagrams can be used
to represent these
relationships.
• These diagrams can illustrate
which animals evolved from
common ancestors and at
what time in the past this
occurred.
Homologous and Analogous
Structures
• One way to determine the relationship among organisms is to find
characteristics they share that they inherited from a common
ancestor. These similar features are called homologous
structures.
• The forelimbs of these four animals are homologous – they are all
made up of the same types of bones.
Homologous and Analogous
Structures
• Not all similarities mean that
organisms evolved from a
common ancestor.
• When organisms evolve
similar traits because they live
in similar environments we call
that process convergent
evolution.
• The features shared by the
organisms through convergent
evolution are called
analogous structures.
Evidence From Fossils
• Fossils are traces or remains
of dead organisms that have
been preserved by natural
processes.
• Fossils can be formed when
organisms are trapped in
amber or in ice. Fossils can be
formed by the gradual
replacement of the organism’s
remains by other substances.
Fossils can be formed if the
plant or animal creates an
impression.
The Age of Fossils
• A fossils relative age can be
determined by observing the
layers of sedimentary rock in
which the artifact was found.
• The age of the fossils found in
the layers can be related to the
ages of the layers..
• This method in which we are
able to determine if one fossil
is younger or older than
another is called relative
dating.
The Age of Fossils
•
Determining when the fossil was actually formed is called absolute dating and
depends upon radioactive isotopes.
•
Over time, radioactive isotopes decay into different elements. By measuring the
amount of each element present in the sample, the length of time since the fossil was
formed can be calculated.
•
For example, over time carbon-14 will decay into carbon-12. Carbon dating can be
used to date the remains of living organisms that are less than 50,000 years old
Evidence From Comparative
Anatomy
• Organisms may have body
structures which have no
function but are similar to more
fully developed structures in
another organism – these are
called vestigial structures.
• Humans posses a vestigial
structure called the appendix
at the base of the small
intestine. The appendix is
similar to the cecum in rabbits
which is used to digest plant
materials.
Evidence From Comparative
Anatomy
• The fact that a similar organ in one species is still useful
is evidence that humans evolved from an ancestor that
once had this larger, functional structure.
• These vestigial structures support the idea that species
have evolved over time as a result of natural selection.
Evidence From Comparative
Embryology
• Embryos of various
organisms are
surprisingly similar.
• At this first stage of their
development, each of
these embryos has a tail
and slits in its neck.
• These similarities indicate
that long ago these
animals shared a
common ancestor.
Evidence From Comparative
Biochemistry
• Biochemistry is the
chemistry of living things.
• All organisms store
genetic information that is
passed on from one
generation to the next in
DNA molecules in a
manner that is almost
exactly the same.
Evidence From Comparative
Biochemistry
• Proteins are molecules in
living organisms used to
build structures, to
transport materials, to
send signals, to provide
defense and to control
metabolic activities.
• Proteins from different
species can be
compared. Those
species with the fewest
differences are more
closely related.
Evidence From Comparative
Biochemistry
• During DNA
hybridization, DNA
from two different
organisms can be
compared to see how
similar they are.
• The more similarities
the more closely
related the species
are.
Patterns of Evolution
• Most often as species
evolve from a common
ancestor they become
increasingly different from
each other – this is
known as divergent
evolution.
• Animals that are not
closely related but have
developed similar
adaptations exhibit
convergent evolution.
Patterns of Evolution
• Parallel evolution is
when two distinct species
which have evolved from
a common ancestor
continue to change in
similar ways.
• Both pterodactyls and
birds developed the body
structures necessary for
flight separately from
each other.
Patterns of Evolution
• Because the environment
always includes other
living organisms, species
frequently change
because of, or along with,
changes in species
around them.
• Evolving alongside
another species is called
coevolution.
Pace of Evolution
• Researchers disagree
about the details of the
process of evolution.
• When evolution occurs
through small, steady steps,
we call the process
gradualism.
• When evolution occurs in
sudden big jumps with long
periods of little or no
change, we call the process
punctuated equilibrium.
Extinction
• Extinction is the
disappearance of a species
from Earth.
• Extinction occurs when a
species is no longer able to
produce more members of its
own type because it can not
adapt to the environment.
• Human activities have had a
significant impact on the rate of
extinction.
• Before a species becomes
extinct they become
endangered – examples
include the African elephant
and giant panda.
Taxonomy
• Taxonomy is the science of
naming and classifying
organisms according to shared
characteristics.
• Organisms are grouped
according to their evolutionary
relationships – the smallest
group is the species, similar
species placed together in a
larger group called genus.
• Kingdom, Phylum, Class,
Order, Family, Genus,
Species.
Taxonomy
• The five main Kingdoms
include: Monera, Protists,
Fungi, Plants and Animals.
• The scientific name of a
species consists of two parts –
the first part is the genus, the
second part is the species or
specific name.
• For example a red oak is
Quercus rubra, a white oak is
Quercus alba. This taxonomic
naming system is called
binomial nomenclature.
The Search for Human Origins
• About 130 million years
ago, reptiles such as
dinosaurs were the
dominant large animals
on Earth – in a relatively
short period of time, they
became extinct.
• About 70 million years
ago, faced with fewer
reptile competitors, an
enormous variety of
mammals evolved.
The Search for Human Origins
• One groups of mammals
called primates, used
opposable thumbs to adapt
to life in trees.
• The order of primates
includes prosimians,
monkeys, apes, and
humans.
• The higher primates
including apes and humans
are known as hominids.
Hominids: The Earliest Humans
• Approximately 20 million years
ago, large changes in climate
caused forested areas to
diminish.
• An African Ape evolved and
that became the common
ancestor of both chimpanzees
and humans.
• This does not mean that our
ancestors were chimpanzees –
it does mean that we are
closely related.
Why Did Early Hominids Walk on
Two Feet.
• Our earliest hominid ancestors
lived in the trees – due to a
changing environment, there
was a shift from the forests to
the open grasslands.
• By being upright in the
grasslands, early hominids
could see danger approaching.
• This could be a tremendous
evolutionary advantage and
could have easily led to the
evolution of life on two feet.
Our own Genus
• Hominids in the genus Homo
are characterized by having
large brains, which sets them
apart from all other primates.
• Homo erectus is considered to
be the first ancestor within our
genus.
• H. erectus was known to build
fires, live in caves, wear
clothes and manufacture tools
Our own Genus
• Homo erectus colonized a
variety of places in Africa,
Asia, Europe and Australia.
• These early humans included
the Neanderthals and the
Cro-Magnons, known for
there large brains, tools, and
clothing.
• Our own species, Homo
sapiens evolved from H.
erectus – exactly where and
when is still being debated.