Evolution
What We Now Know
The “Theory” of Evolution
 Humans have come a long way!
 Have you ever stopped to wonder what mechanisms
fueled our evolution?
 Why have we inherited some traits from our parents
and lost others?
 Evolution is a hot topic in science. Everything is
changing in our world.
In this unit we will look at:
Mechanisms of Evolution:
Evidence of Evolution:
- What caused the world to evolve
into what we see now?
- Mutations
- Genetic drift
- Gene Flow
- Sexual Selection
- Natural Selection
-Good scientists want proof!
-Geology
-Fossil Record
-Biogeography
-Comparative Anatomy
- Molecular Biology (DNA)
History of Evolutionary
Thought
Creationism
The early ideas about the natural world were
heavily influenced by Plato and Aristotle.
Early Christians built upon this idea, and
concluded from the biblical account of
creation that God had created each species
individually.
The traditional Judeo-Christian version of
creationism was strongly reinforced by
James Ussher , a 17th century Anglican
archbishop of Armagh in Northern Ireland. By
counting the generations of the Bible and
adding them to modern history, he fixed the
date of creation at October 23, 4004 B.C.
Evolution
vrs
The Creation of
Adam is a section of
Michelangelo’s
fresco on the ceiling
of the Sistine Chapel
painted in 1511.
 By the 18th century, the tide had begun to turn in favor
of evolution.
 People were not quite sure how evolution happenedCharles Darwin and Alfred Russel Wallace had not
thought of Natural Selection.
Jean-Baptiste Lamarck’s inheritance of acquired traits
was the most commonly accepted mechanism for
evolutionary change.
Early believers may have been wrong about how it
happened but give them credit for at least understanding
that it did happen.
 Evolution is the process in which significant changes
in the inheritable traits (genetic makeup) of a species
occur over time.
 What evidence supports this change of thinking?
1. Geology
 The earth is 4.6 billion years old.
 James Hutton – father of modern geology
 Hutton’s observations of geological processes led him to the
concept of uniformitarianism (processes that operate today
are the same processes that operated in the past)
 Charles Lyell popularized the principle of uniformitarianism.
 Lyell and Darwin were friends.
 Darwin’s musings on natural selection were influenced by
the idea of uniformitarianism.
 Hutton and Lyell laid important groundwork for
evolutionary thought.
 Geology and uniformitarianism were critical in showing
that the earth had been around long enough for
evolution to occur.
Charles Lyell
 Proposed that the earth’s surface has changed and
continues to change through similar gradual processes.
 1851 visited Joggins
Stratigraphy – the study of layers of rocks and sediments
Ages of Rocks

Relative Age – age of rocks and the relative age of fossils can be determined by
the chronology of the rock layers. Oldest on bottom, youngest on top.

Absolute Age – determined by radioactive decay (radioactive dating using half
lives)

C14 has a half life of 5730 y

K 40 has a half life of 1.3 b.y.
2. Fossil Evidence
- Fossils show evidence of organisms that were once
alive.
- It also shows the record of the extinction of many
others.
Fossil Evidence
- Shows a record of the diversification of species
 What exactly is a fossil:
- Any preserved remains or traces of an organism or its
activity.
- In 1669 Nicholas Steno detailed an impressive analysis
of fossils showing that they were the remains of living
organisms
- fossils form in sedimentary rocks
How does a fossil form?

Organisms must die and then be rapidly buried to prevent scavengers or rapid
decomposition (if there are only soft parts).
There are two types of
fossils:
 Body Fossils which are actual remains:
Includes actual bones, shark’s tooth, petrified wood,
frozen mammoth, insects in amber.
 Trace Fossils which include: Mold or Cast formed by
replacement
Or footprints, worm trails, coproliths, or
stomach stones
 English geologist William Smith (1769-1839) realized that
certain fossils always showed up in the same kinds of rocks,
even if they were found in different locations.
 Smith called the predictable layering of fossils the Principle
of Faunal Succession, because animals (fauna) in the layers
always occurred in the same order (succession).
 Fossils in layers closest to the surface (youngest) most
closely resemble living organisms where fossils in lower
layers (older) look very different from living organisms.
 Some organisms in older layers no longer exist (extinct).
Index Fossils
 Used to determine ages of rock layers
Examples of index fossils:
 Short lived, easy to identify
Mass Extinctions
 Why are mass extinctions important?
 They stimulate new biodiversity!
 No competition.
 Fossils show transitional forms. They show
intermediate stages as an organism evolves from one
thing into another.
 These transitional fossils provide direct evidence that
life forms change over long periods of time.
 3. Biogeographic distribution of living species gave
scientists clues to the patterns of evolution
If a group of related species all descended from a common ancestor,
they should share many similarities even if they evolved different
lifestyles.
4. Structures – Homologous
and Analogous
 Homologous- structures that share a common origin
but may serve different functions in modern species
Long bone
Two short bones
1) Salamander, 2) Frog, 3) Turtle, 4) Aetosaurus, 5)Pleisiosaurus,
6) Ichthyosaurus, 7) Mesosaurus, 8) Duck.
 Example of Homology:
the tetrapod limb
 The wing of a dragonfly and the wing of a butterfly are
homologous — they were both inherited from an
ancient flying insect.
 Not all homologies are obvious if they have been
adapted for different roles. For example, the chomping
front teeth of a beaver look quite different than the
tusks of an elephant. Each is a modification of the basic
incisor tooth structure
 Homologies show that Divergent Evolution takes
place
Divergent Evolution:
A common ancestor evolves into new species, which
continue to evolve and become less and less alike over
time due to differences in the demands driven by the
environment.
 Brown Bears and Polar Bears illustrate divergent
evolution.
 Scientists think that a long time ago a group of Brown Bears became
geographically separated from the rest. This isolated group acquired new
characteristics, such as the ability to eat meat, blubber to keep warm in
snowy weather, and a white coat for camouflage. They slowly evolved into
Polar Bears
 Analogous – structures similar in function but not in
origin
So what about ANALOGY??
 Consider the following example....
 Both are extinct animals and both of them have saberteeth...but are they
homologous??
(Consider that Australia had separated from the Supercontinent a
loooooong time ago)
Thylacosmilus,
a marsupial mammal
Smilodon, the saber-toothed cat,
which is a placental mammal
analogy
similarity due to convergent evolution not
common ancestry
CONVERGENT Evolution: When two separate groups of
animals evolve to have similar structures
How do analogies evolve?
Often, two species face a similar problem or challenge.
Evolution may then shape both of them in similar ways —
resulting in analogous structures.....like the saber teeth.
Another good example of Analogous structures......
While sugar
gliders
(marsupials)
superficially
resemble the
placental flying
squirrels of
North America,
the ability to
glide through
the air evolved
independently
in these
unrelated
mammals.
So there you have it.....
HOMOLOGY vs.
ANALOGY
5. Embryonic Development – Embryos of different
organisms can have homologous features
 Human embryos have a tail
6. Vestigial Features- Structures which serve no useful
function in a living organism
 Digits (dogs)
 Hipbones (whales)
7. Molecular Biology
 The tools of modern molecular biology were not available to
early evolutionary thinkers.
 We know that similar chemistry, structures and processes
underlie all cells. (All cells have mitochondria). All cells have
ribosomes which assemble proteins based on genetic code.
 Molecular biology shows the degrees of relatedness
between different organisms.
 By sequencing certain genes and comparing them in
different organisms, scientists can figure out who is more
closely related.
 For aficionados of gigantic Ice Age mammals, woolly
mammoths provide a cool example of how gene sequencing
reveals information about the evolution of elephants and
their relatives. In 2006 an international group of scientists
sequenced genes from extinct wooly mammoths—itself a
remarkable feat. Mammoths are often found in permafrost,
extremely cold soil, which provides ideal conditions for
preserving DNA. The research team compared mammoth
gene sequences to two different kinds of elephants living
today: modern Asian and African elephants. They
discovered that the closest living relatives of mammoths are
Asian elephants. In other words, mammoths and Asian
elephants share more of their DNA and a more recent
common ancestor than modern Asian and African elephants.
A Special Note About
Mutations:

Mutations occur every time our genetic material is replicated; it
doesn't happen very often, but every once in a while a base pair might
be added, deleted, or changed. It is estimated that 300 new mutations
are introduced into the human genome every generation—that is, you
have 300 new mutations compared to your mom and dad! Assuming
these mutations occur at a somewhat constant, predictable rate, we
can reason that the more time that has passed since two organisms
diverged from each other, the more different their DNA will be. Just
think, taking into account 300 new mutations every generation, your
child would have 600 new mutations compared to your parents and
your grandchild would have 900 new mutations. Over time, these
accumulate in the genome, adding to the differences observed
between organisms. In other words, more similar DNA sequences can
mean that two organisms are closely related, and very different
sequences indicate that they split from each other a longer time ago.