How the Theory of Evolution was Formed
Theory of
Acquired
Characteristics
Use and
Disuse
Jean Baptiste Lamarck
• Species evolve over time
• Species evolve to become
better adapted to their
environment
• Changes are passed on
from generation to
generation
**it is the mechanism that still needed to be
Scientists that Contributed
to our present Theory of Evolution
Georges Cuvier
Catastrophism
• Species evolve over time
• Species evolve to become
better adapted to their
environment
• Changes are passed down
from generation to
generation
• Species evolved from
simple to more complex
Scientists that Contributed
to our present Theory of Evolution
Charles Lyell
Uniformitarianism
• Species evolve over time
• Species evolve to become
better adapted to their
environment
• Changes are passed down
from generation to
generation
• Species evolved from
simple to more complex
• Geological change is slow
and gradual – and
therefore so was
evolutionary change
Speciation Dynamics - Gradualism or Punctuated Equilibrium?
The theory of gradualism states that as
new species evolve, they appear very
similar to the original species and only
gradually become more distinctive
e.g. Whales and Horses
The theory of punctuated equilibrium
suggests that the process of evolution is
slow, but is occasionally punctuated by
periods of rapid change
e.g. Hawaiian Honeycreepers
This theory explains the lack of fossils
of transitional species due to the fact
that speciation usually occurs small
isolated populations
It is now widely accepted that both
play a significant role in evolution.
Two Patterns of Speciation
So Does Evolution Create the Perfect Organism?
No, only better organisms as evolution
is constrained by history and buffeted
by random events.
Essentially, every organism on earth is
in significant part a sum of accidents.
Evidence for Evolution
Biogeography
Homologous
and Analogous features
Embryology
Vestigial
features
Competition within Populations
What set apart Darwin’s theory from other scientists’ was
that it explained how species had evolved, using amassed
evidence.
7.3 Darwin’s Voyage on the HMS Beagle
Biogeography evidence for evolution
Biogeography
Geographic patterns of distribution
Fossil evidence suggest that ancestral
species evolved separately once the
supercontinent, Pangaea, separated.
Endemic species evolved a lack fear of
predation
Red colobus monkey
(endemic to
Zanzibar, Tanzania
Homologous Structure/Feature
Similar structures found on different species that have entirely
different functions.
E.g. Same (but modified) bones and relative positions
Embryology
The embryos of all vertebrates,
including humans, chickens,
and fish, share a similar
pattern in development
Provides evidence of
evolutionary relationships
between species
Analogous Structure/ Feature
Structures in different species with the same appearance, structure,
or function but have evolved separately, thus do not share a common
ancestor.
E.g. wings of insects and birds used for flying
E.g. fins of fish and flippers of whales used for swimming
Vestigial Features
Physical features that exist with no practical function
Competition WITHIN Populations
A limiting factor to survival is always FOOD SUPPLY
All species produce more offspring than can survive to reproduction
This results in a competition for resources, especially when the
number of individuals exceeds the amount that can be supported by
the habitat.
Modern Evidences of Evolution
Pseudogenes
Homologous Genes
Plate tectonics
Paleontology
How does evolution occur?
Evolution of a
Species
Core principle:
Beneficial
Neutral
Mutations
Harmful
Genetic Variation
in a Population
Selection
Pressure
•
•
•
•
Natural Disaster
Mate Selection
Climate Change
Artificial Selection
How might it be possible
for a neutral mutation
to play an important
role in the evolution of
a species?
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