Download Evolution:

Evidence supporting theory of
evolution
• Analogous structures
– Structures similar in
form and function.
• Develop as a result of
convergent evolution?
Evidence supporting theory of
evolution
• Life’s chemistry
– Organisms are made of molecules and
studying the molecules can help us
understand possible relationships.
– Example: Proteins
• Made of amino acids bonded together.
– Similar to a strand of pearls.
• More closely related two organisms are, the more
closely their proteins resemble each other.
Speciation
• Speciation: species giving rise to new
species.
– Some segment of original population must be
isolated from the rest.
• Reproductive isolation is an essential ingredient.
• Occurs via two mechanisms:
– Allopatric Speciation
– Sympatric Speciation
Allopatric speciation
• Definition: Speciation
that occurs between
isolated populations.
– Originated in different
fatherlands.
• Must be
geographically
isolated.
Allopatric speciation
• To reach and colonize new area, must realize
three opportunities:
– Geographic
– Physiological
– Ecological
Sympatric speciation
• Definition: Speciation
among populations
whose ranges
overlap.
– Occur in same
fatherland.
• Can occur with
species occupying
different habitats, but
in the same range.
• Both types of speciation
can be occurring at the
same time.
– Initially population is
geographically isolated.
– If geographic barrier is
removed, populations
overlap.
– Could still be isolated by
differences in preferred
habitat, courtship displays,
breeding season,
preferred.
• If not isolated by differences, then two
populations will merge into one species.
Patterns in Evolution
• Convergent evolution
– Unrelated species living in similar environments and
facing similar environmental challenges sometimes
evolve similar characteristics.
Patterns in Evolution
• Divergent evolution
– Closely related species living in different
environments and facing different environmental
challenges sometimes evolve dissimilar
characteristics.
Patterns in Evolution
• Adaptive radiation
– Sometimes, several
species will evolve
from a single,
ancestral species.
Patterns in Evolution
• Coevolution
– Evolution of one species affects the evolution of
another species.
• As predators evolve, prey evolves. As prey evolves,
predators evolve.
– Example: Cheetahs feed on Thompson’s gazelles
• As the speed of one population of cheetahs improves so
does the speed of the Thompson’s gazelles .
Patterns in Evolution
• Gradualism
– Evolution may occur
as a slow, gradual
process of change.
• Theory favored by
early evolutionists.
Patterns in Evolution
• Punctuated equilibrium
– Evolution may proceed with
long periods of relatively
little change (stasis)
punctuated with short
periods of intense change.
– Examples: House flies,
trilobites, antibioticresistant bacteria.
Evolution does not always occur
• Natural selection can
only work on existing
variation.
• Variation cannot be
created on demand.
• Some species lack
range of variation to
support evolution.
Results of evolution
• Everywhere we look on the Earth, you can
find organisms.
– Scientists have described 1.5 millions species
• Still many species yet to be described.
– Predictions indicate there may be 10-100
times as many species as those already
described.
Darwin’s Theory Debated
• Three main criticisms:
– Darwin lacked direct evidence for natural
selection.
• Indirect evidence was unconvincing
– Darwin could not explain the source of
variation in a population and inheritance of
variation.
• Answered by an understanding of genetics
– What is the rate at which organisms evolve?
• Slow and continuous or jerky and discontinuous?
Darwin recognizes three special
cases of natural selection
• Sexual selection explained flamboyant appearance
amongst birds.
– Sexual selection: female birds choose mates and are attracted
to males with extreme features.
– Females breed with them and extreme features passed to
offspring.
Darwin recognizes three special
cases of natural selection
• Altruism
– Individual behavior
benefits a social group
often at the expense of
the individual.
• Example: worker bees
in a hive
• Kin Selection
– Individuals help kin
raise their young.