Download CHAPTER 28: EVIDENCE OF EVOLUTION

UNIT 5 PART 1: EVIDENCE OF EVOLUTION
Evolution is a gradual change over time.
 There are two kinds:


Geological – a change in the earth over time

Organic – a change in species over time
“Seen in the light of evolution,
biology is, perhaps, intellectually
the most satisfying and inspiring
science. Without that light, it
becomes a pile of sundry facts,
some of them interesting or
curious, but making no
meaningful picture as a whole.”
--Theodosius Dobzhansky,
"Nothing in Biology Makes Sense
Except In The Light of Evolution,"
1973

Evidence from the Past - Fossils
A fossil is any trace or remains of an
organism that has been preserved by a
natural process.
 Scientists can compare these to living
organisms to see if evolution has occurred.
 Special circumstances are needed for fossils
to form and then usually only the hard parts
are left.

Relative Dating of Fossils
Most fossils are in sedimentary rock which
forms layers.
 If the layers are undisturbed the oldest is on
the bottom and the youngest on top.
Therefore, the oldest fossils are found in the
bottom layer.
 This tells you which fossils are older.
 Determining the order of the fossils results in
the fossil record.

Absolute Dating of Fossils
This will tell the
actual age of the
fossil.
Radioactive
Dating is the most
accurate.
Matching layers in
the same region
are the same age.
This is called
correlation.

These are
fossils that
appeared
around the
same time all
around the
world.
 They can be
used to match
ages of rock
layers in
different parts
of the world.

Index Fossils
Patterns of Evolution
Earliest organisms were simple, later ones more complex.
 Unicellular organisms appeared before multicellular.
 Aquatic organisms appeared before land animals.

There are sequences in the fossil record that
indicate that later species developed from
earlier ones through a series of gradual changes
passed on from generation to generation.
These occurred over millions of years in the
species. The fossil record is considered the
strongest evidence of evolution.
Extinction
Of all the species that ever lived
less than one percent exist
today.
 When the last of a species dies
that species is said to be extinct.
 Extinction is forever.

Quagga 1883
Golden Toad 1989
Tasmanian Tiger or
Tasmanian Wolf 1936, 1986
Passenger
Pigeon
1914
Evidence from Living Organisms
The classification system
that we use is based on
similarities and
differences in anatomy,
embryological
development, and
biochemistry.
 Similarities indicate a
common ancestor. The
more similarities
between organisms the
more closely related they
are.

Anatomical Similarities

Vestigial structures – parts that are reduced in size
and have little or no function.
Human appendix, tail bone, wisdom teeth and muscles
that move the ears and nose
 Whale hip and leg bones

Homologous Structures

Parts that have similar structures and
development (are built the same way) but
have different functions:
Human arm
 Cat leg
 Whale flipper
 Bat wing


Indicates a common ancestor
Analogous Structures

Parts that have the same function but a
different structure and development (they
are made differently):
Bird wing
 Insect wing


Indicates evolution along different lines
Embryological Similarities
The embryos of
closely related
species show
similar patterns of
development.
As development
continues the
embryo resembles
the adult.
The longer the
embryos
resemble each
other, the closer
related they are.

Molecular Similarities
The ability to read the amino acid sequence of
proteins and the DNA of an organism letter by
letter has enabled biologists to confirm
evolutionary relationships.
 The more closely related
organisms are, the
greater the biochemical
similarities will be in the
sequences of DNA,
proteins, and enzymes.

The Origins of Life –
Modern Hypothesis
Biogenesis – living things come only
from other living things.
So where did the first living things
come from?
The most widely accepted view is the
heterotroph hypothesis.

Heterotroph Hypothesis

Early conditions on Earth were different:
Higher temperature
 Different atmospheric composition

The oceans were a hot, thin soup where
chemical reactions were
likely to occur.
 An experiment by Miller
showed that organic
compounds could be
formed under these
conditions.

cont’d.
These organic compounds then formed structures
that had some of the characteristics of life and
began to grow and divide. They were called
heterotrophs.
 Eventually organisms developed that could use
light for energy and produce oxygen - autotrophs.
 This changed the makeup of the atmosphere
which led to the development of organisms that
could use oxygen for respiration.
 Because aerobic respiration is more efficient than
anaerobic, organisms using aerobic respiration
became dominant.
