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Theories of Evolution
Lamarck’s Explanation (1744-1829)
 Hypothesized that
similar species
descended from the
same common
ancestor
 Acquired traits –
traits that arise
during an organism’s
lifetime because of
their experiences or
behaviors
Beginning of the Modern Theory
 In the mid 1800’s both
Charles Darwin and
Alfred Wallace proposed
the theory of Natural
Selection.
 Organisms best suited
to their environment
reproduce more
successfully than others.
Charles Darwin
 Published the Origin of Species in 1859
 Sailed around the world on the HMS Beagle
studying different species in their natural
environment
 Did a lot of his studies in the Galapagos Islands
Darwin’s Theories
Descent With Modification
 Newer forms of organisms appearing are
actually modified descendants of older
species
Darwin’s Theories
Modification By Natural Selection
 This theory states how evolution occurs
 Darwin agreed w/Malthus’ views on
human population – have the potential for
growing unchecked but are limited by
adverse conditions
 Environment limits growth of populations
Modification by Natural Selection
 Some organisms have
traits that make
them more suitable
for coping with their
environment.
 Organisms with more
of these traits tend
to leave more
offspring
Evidence For Evolution
The Fossil Record
 Shows a long history
of life on Earth
 Shows that forms of
organisms appeared,
lasted for long
periods of time, then
disappeared to be
followed by newer
forms of life
Fossils
 Trace of organisms
 Develop from hard parts – shells, bones,
teeth
 Law of Superposition- Sedimentary rock
layers - lowest layer is oldest
 Relative Age
 Absolute Age
Evidence for Evolution
Comparative Anatomy – study of structural
similarities and differences among living things
The presence of certain types of similarities
offers evidence for the evolutionary
relationships between species.
Homologous structures
 Parts of different organisms that have
similar structures and similar
embryological development, but have
different forms and functions
 Give evidence that some species may
have evolved from common ancestors
 Ex. Structure of arm and hand of human,
whale, cat, bird, bat
Analogous Structures
 Structures that
have similar external
form and functions
but different
internal structures
 Ex. Wings of moth
and bird
Vestigial Structures
 Remnants of structures that were functional in
an ancestral form
 Ex. Appendix, human tailbone, pelvic bones of
snakes
Evidence for Evolution
Embryological Similarities
 Embryos of closely related species show
similar patterns of development
 Ex. Fish, pig and human embryos look
similar see page 223 or color plate 5-3
Evidence For Evolution
Macromolecule Similarities
 Molecular level –
homologous proteins
 Ex. The amino acid
sequences in hemoglobin
molecules of different
species are similar
 The more similar the
homologous proteins are
in different species, the
more closely related the
species are thought to
be
Patterns of Evolution
Coevolution
 Change of two or more species in close
association with each other
 Ex. Long-nosed fruit bat has coevolved with
the flowers they feed on
 Predator-prey relationships and parasite-host
relationships often coevolve
Patterns of Evolution
Convergent Evolution
 Organisms that seem
very similar but not
closely related at all
 Occurs when
environment selects
similar phenotypes
even though
ancestral types were
quite different
 Ex. Sharks and
porpoises
Patterns of Evolution
Divergent Evolution
 Two or more related populations of
species become more and more dissimilar
 Almost always as a response of differing
habitats and can ultimately result in a
new species
Divergent Evolution
Adaptive Radiation
 Many species evolve from a single ancestral
species – ex. Galapagos Finches
Artificial Selection
 Process of speeding up divergence artificiallyex. Dog breeding