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Lesson # 2: Evolution
“Evidence for Evolution”
Evidence Supporting Theories of Evolution
We will look at major evidence supporting theories
of evolution:
1. Fossil Record
2. Comparative Anatomy
3. Biogeography
4. Biochemistry
Fossil Record
Fossil Definition
Any ancient remains, impressions, or traces of an organism
or traces of its activity that have been preserved in rocks or
other mineral deposits in Earth’s crust
Hard impressions in solid rock and leave little doubt as to
what they represent
Fossil Formation
Fossils are formed when the remains of a buried organism
are gradually replaced by mineral deposits
Once a body dies the body usually decomposes
When sediments accumulate over time the body becomes
compressed, and gradual chemical changes occur that result
in the body being mineralized
Only organisms that die in low – oxygen locations will
fossilize
How fossils
are formed
Fossil Record Continued
Organisms with hard body parts (shells, bones, teeth) are
more likely to be preserved
Fossils of aquatic organisms are very common rather than
fossils of land animals and plants
Dinosaur fossils are well known but very rare compared to
those of aquatic organisms
Fossils can also be formed from footprints and burrows
Organisms can also become trapped in materials that
preserve its chemical remains i.e. tree sap, volcanic ash,
permafrost, acidic bogs
Reading the Fossil Record
Paleontology
The scientific investigation of prehistoric life through the study
of fossils
Discoveries about fossils:
1) Many fossils appear to be of unusual and unknown organisms
2) There are no fossils of most living species
3) Fossils are often buried very deep within rock formations
4) Fossils are often found in unexpected locations (i.e. fossils of
sea life are found high in mountain formations in present – day
deserts)
These contradicted prior views that fossils were nothing more
than organisms that had become trapped in muddy deposits and
then hardened
Georges Cuvier
 Conducted the first detailed studies of
fossils
 Noted the following:
Fossils are very simple organisms are
found in all depths of fossil deposits
Fossils of more complex organisms are
found only at shallower depths, in
younger rock
Fossils in the shallower depths are more
likely to resemble living species
Rock layers contain fossils of many
species that do not occur in layers above
or below them
How Fossils Support Theory of
Evolution
Life had evolved from simple to more complex forms over time
Species themselves do not change, instead theory of catastrophism
Catastrophism
The theory that the pattern of fossils could be accounted for by a
series of global catastrophes that wiped out most species on Earth
Cuvier discovered that different groups of species get more
complex in each younger layer but not why this happened
 Recall Lyell
 Proposed that Earth’s geological features can be explained by very
slow changes occurring over very long periods of time
Darwin’s Hypothesis
Theory that species evolved
Hypothesized that remote oceanic islands became populated by
species that arrived by water or air
After the species became established, many evolved into new
species over time
“Tree Thinking”
 Implies that all organisms are related
 According to the principle of common descent, all species
living or extinct are descended from common ancestors
Darwin’s Hypothesis Regarding Remote
Islands
Observations on Galapagos Islands
Darwin’s Hypothesis
Many species of plants, birds, insects
and in some cases reptiles
Only these kinds of organisms are
able to reach remote islands by
crossing large expanses of open ocean
No native amphibians and very few
land mammals
Amphibians and most mammals are
unable to cross open ocean and will
not be found on remote islands
Many unique species found nowhere
else on Earth
Over time, ancestral species have
evolved into new geographically
isolated species
Unique species most closely resemble Unique species are descendants of
species on the nearest continental land ancestral species from the nearest
mass
continental land masses and will
exhibit some similarities
Comparative Anatomy
(Homologous Features)
 Homologous Feature
A structure with a common evolutionary origin that may
serve different functions in modern species
i.e. bat wing and human arm
Similar structures of two organisms could have entirely
different functions
Similar in origin
Different in function
May appear in embryonic
development and disappear
before birth
Existence of homologous structures adapted to different purposes as a
result of descent with modification from a common ancestor
Comparative Anatomy
(Analogous Features)
 Analogous Feature
A structure that performs the same function as another but is not
similar in origin or anatomical structure
i.e. wing of bee and wing of bird
Different in origin
Similar in function
May appear in embryonic development and disappear before birth
Comparative Anatomy
(Vestigial Features)
 Vestigial Features
A rudimentary and non – functioning, or only marginally
functioning, structure that is homologous to a fully functioning
structure in closely related species
i.e. hipbones of bottleneck dolphins
 Relation to Evolution
 Features that in an ancestor had once served a useful purpose
had become useless or greatly distorted as the species evolved
Biogeography
 Biogeography
The scientific study of the geographic distribution of organisms based on
both living species and fossils
 Darwin’s Discoveries
Looked at finches on the Galapagos islands
Populations on islands evolved from mainland species
Natural selection on islands produced variations among populations
(resulting in different but closely related island species)
Beak depth, and the ability to crack larger seeds, varies according to
drought conditions, which produce fewer, harder seeds in dry years and
more and softer seeds in wet years
Consistent environmental differences in different habitats on different
islands in the Galapagos, as well as the availability of different foods
sources, have produced more than a dozen distinct species of finches, all
unique to the archipelago.
Natural selection shaped beaks as became adapted to eat different foods
Biochemistry
 Genetic and Molecular Biology
Some of the most crucial evidence comes from genetics
At the molecular level, universal genetic code and homologous
molecules provide evidence of common descent
Also, mutations and reshuffling of genes during sexual
reproduction produce heritable variation on which natural
selection operates
THE END!!