HONORS LIVING ENVIRONMENT
TOPIC 22: EVOLUTION AND BIODIVERSITY
MS. ETRI
PART 4: EVIDENCE OF EVOLUTION AND EVOLUTIONARY TREE DIAGRAMS
WHAT EVIDENCE DO WE HAVE THAT EVOLUTION EXISTS?
1. THE FOSSIL RECORD

FOSSILS—Imprints or remains of organisms that lived in the past.
o
Fossils document differences between past and present organisms, and the fact that
many species have become extinct.
o
The organic substances of a dead organism usually decay rapidly, but the hard parts of
an animal that are rich in minerals, such as the bones and teeth of vertebrates and
shells of clams, may remain as fossils.
o
Are found in sedimentary rock.

The fossils that are found in a particular stratum (layer of rock) provide a glimpse
of some of the organisms that lived in the area at the time the layer formed.

Because younger strata are
found on top of older ones, the
relative ages of fossils can be
determined by the layer in
which they are found.

Newer fossils form in
each subsequent layer
of sediment that gets
laid down, so the
deeper the fossil, the
older the organism.

The fossil record is incomplete!
o
Many of Earth’s organisms did not live in areas that favor fossilization.

Many fossils that did form were in rocks later distorted or destroyed by geologic
processes.

Not all fossils that have been preserved are accessible to paleontologists
(scientists who study fossils).

By examining the fossils in each layer of rock, we can see how anatomical structures have
changed throughout the history of life.
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2. COMPARATIVE ANATOMY

The study of the anatomy of various animals.

HOMOLOGOUS
o
Scientists have discovered that some animals have similar structures that serve
different functions.

EXAMPLE: a human’s arm, a dog’s leg, a bird’s wing, and a whale’s fin are the
same appendages , though they have evolved to serve different functions.

These structures are known as homologous structures—show evidence of
common ancestry.

If mammals weren’t evolutionarily related, it seems weird that they would all end
up with such similar bones!
o
HOMOLOGY—characteristics in related species can have an underlying similarity even
though they have very different functions. (Similarity resulting from common
ancestry.)

ANALOGOUS
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o IN CONTRAST, some animals have features with the same function but are
structurally different.
o
EXAMPLE: A bat’s wing an insect’s wing are both used to fly (same function), but have
evolved totally independent of one another.

These are called ANALOGOUS STRUCTURES
3. COMPARATIVE EMBRYOLOGY (EVO-DEVO)

The study of the development of an organism.

If you observe all of the early stages in vertebrate development, all the embryos look
alike.

All vertebrates—including fish, amphibians, birds, and humans, show fishlike features
called gill slits.

Anatomical homologies in embryos are not visible in adult organisms.

This provides evidence that all organisms came from a common ancestor.
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4. COMPARATIVE BIOCHEMISTRY
MS. ETRI

Shared characteristics on the molecular level.

Scientists can examine the nucleotide and amino acid sequences of different organisms.

From these analyses, we’ve discovered that organisms that are closely related have a greater
proportion of sequences in common than distantly related species.
o

As much as 99% of our genetic code is identical to that of a chimpanzee.
EXAMPLES: All life forms use the same genetic language of DNA and RNA; amino acid
sequences coding for hemoglobin in primate species shows great similarity, thus indicating a
common ancestor.
Which
species is
most common to the unknown? Species IV
**ALL OF THE ABOVE STUDIES SUPPORT THE THEORY OF EVOLUTION, PROVIDE EVIDENCE OF
GRADUAL CHANGE OVER TIME, AND ARE PROOF THAT ALL ORGANISMS ONCE DERIVED FROM A
COMMON ANCESTOR**
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EVOLUTIONARY (PHYLOGENETIC) TREE DIAGRAMS
MS. ETRI
 Diagrams that map out what happens to various species over the course of time and help
determine evolutionary relationships between species.
 From these diagrams you should be able to determine the species that are:
o most closely related (ones that share the most recent common ancestor)
o distantly related
o extinct (no longer living today)
Example:
*Which species currently exist in the
present day? ________________________
*Which species is most closely related
to organism J? __________
*Which species is most closely related
to organism P? __________
*What is the most recent common
ancestor of species M and P? ___________
*Which species are extinct?
______________________________________________
*What species is the common ancestor
to all organisms?
Additional
______
Examples
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HONORS LIVING ENVIRONMENT
MS. ETRI
of Evolutionary Tree Diagrams
*Which species is most closely related to
species B? _________
*Which species are extinct?______________________
*Which species is the common ancestor to all
other species? ____________
*Which species is most closely related to
the Steller’s sea cow? ________________________
*Which species is most closely related to
the Brazilian manatee?
___________________________________________________
*Which species are extinct?
___________________________________________________
___________________________________________________
*What observation can you
make about the diversity
among organisms that existed
long ago, versus the
diversity that exists in the
present day?
__________________________________
__________________________________
__________________________________
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