Natural Selection
• Mechanism for evolution
• Differential survival and reproduction of
chance inherited variants, depending on
environmental conditions
EVOLUTION by
Natural Selection
Differential
Reproduction
Variation in
Traits
Heredity of
the more
advantageous
traits
Biological adaptations include changes in
structures, behaviors, or physiology that
enhance survival and reproductive success in
a particular environment
EVOLUTION
Where is the Proof?
Evidence for Evolution
• What direct evidence supports this theory?
– Changes in populations over time
• Ex: peppered moth
Evidence for Evolution
• What direct evidence supports this theory?
– Structural adaptations
• Ex: mimicry; camouflage
Evidence for Evolution
• What direct evidence
supports this theory?
– Physiological changes
• Ex: drug-resistant
bacteria;
• Ex: pesticide-resistant
insects
EVIDENCE
• Biogeography
– Study of the past and present geographical
distribution of species
• The Fossil Record
– Succession of fossil forms is compatible with what is
known from other types of evidence and the major
branches of descent in the tree of life
• Comparative Anatomy
• Comparative Embryology
• Molecular Biology
The Fossil Record
• Remains of animals and plants
found in sedimentary
rock deposits give us an
indisputable record of past
changes through time.
• This evidence attests to the fact
that there has been a
tremendous variety of living
things.
• Some extinct species had traits
that were transitional between
major groups of organisms.
Their existence confirms that species are not fixed
but can evolve into other species over time.
Comparative Anatomy
• Homology- similarity in characteristics
resulting from a shared ancestry
• Homologous Structures- structures in different
species that are similar because of common
ancestry
Homologies
• Homologies and the
tree of life are
important in explaining
ancestry.
• Homologies shared by a
greater number of
species are likely to
have evolved earlier on
in history and are
further down on the
tree of life.
Homologies
• Homologies that have evolved more recently
are seen on only small branches of the tree.
– Example: tetrapods--the vertebrate branch
consisting of birds, amphibians, mammals and
reptiles.
• They all have the same 5-digit limb structure which
indicates these mammals all share a common ancestor.
5 Digits
Homologies
• Forelimbs of all mammals show the
same arrangement of bones from
shoulder to finger tip.
• These occur even if the structure is
used for a completely different
function.
• These anatomical differences would not
have arisen in a new species if they did
not share a common ancestor.
ARM = carrying
Humerus
Radius & Ulna
Carpals
Metacarpals
Phallanges
Front Leg = walking
Front Flipper = swimming
WING = flying
Homologous Structures:
BONES
A Biogeographical Example:
Homologous vs Analogous
• Eutherians (placental) vs. Marsupials
• Both of these are a type of flying squirrel, but
are unrelated and distinctly different from one
another.
• Marsupials are born as embryos and develop in the
mother’s pouch.
• Eutherians develop completely within the uterus of the
mother.
A Biogeographical Example:
Homologous vs Analogous
• Although the two mammals look similar and
occupy similar niches, the resemblance is not
homologous--it’s analogous and the result of
convergent evolution.
Homology vs. Analogy
Other Similarities Revealed
• Comparative embryology
– Compares structures seen early on in
development--pharyngeal pouches for example.
– Ontogeny Recapitulates Phylogeny
• Vestigial organs
– Organs with little or no use remaining from
ancestral lineages
• Some snakes have vestiges of legs bones and a pelvis
• Coccyx in humans (tail)
Lizard
Tortoise
Pig
Human
Homologies
• Molecular homologies exist as well--the
genetic machinery of DNA and RNA also
points to a common ancestor
– the existence of Hox genes in development.
• Genes and proteins with sequences of monomers that
match indicate that the sequences must have been
copied from a common ancestor
• Explain, using examples, how the fossil record,
comparative anatomy, and other evidence
supports the theory of evolution.
– At least one page, typed, double-spaced, &
sources of info/pics cited.