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Theory of Evolution
Chapter 13
The History of
Evolutionary Thought
 The
development of new types of organisms
from preexisting types of organisms over time.
 Also could be described as a heritable change in
characteristics within a population from one
generation to the next
The primary mechanism of evolutionary change
producing adaptation of organisms to their
environment is natural selection, the differential
survival and reproduction of individuals within a
The History of
Evolutionary Thought
Darwin’s Ideas
 Used
the phrase “descent with modification” to
describe the process of evolution
 Every species, living or extinct, must have
descended by reproduction from preexisting species
and that species must be able to change over time.
Theory of Natural Selection
1. Overproduction
 More
offspring are produced than can survive
to maturity
Theory of Natural Selection
2. Genetic Variation
Within a population,
individuals have
different traits. Ex:
Thick fur
Occasionally, new
traits may appear in a
Theory of Natural Selection
3. Struggle to Survive
Individuals must
compete with each
 Some variations
improve an individuals
chances to reproduce,
but some variations
reduce this chance.
Theory of Natural Selection
4. Differential
Organisms with the
best adaptations are
likely to survive and
Through inheritance,
the adaptations will
become more frequent
in the population
Darwin proposed natural selection as the
mechanism of evolution
Note these important points
Individuals do not evolve: populations evolve
Natural selection can amplify or diminish only
heritable traits; acquired characteristics cannot be
passed on to offspring
Evolution is not goal directed and does not lead to
perfection; favorable traits vary as environments
Copyright © 2009 Pearson Education, Inc.
Artificial Selection
this process occurs when a human breeder
chooses individuals that will parent the next
Fossil Evidence
The fossil record shows that organisms have
evolved in a historical sequence
The oldest known fossils are prokaryote cells
The oldest eukaryotic fossils are a billion years
Multicellular fossils are even more recent
Copyright © 2009 Pearson Education, Inc.
Fossil – the remains or
traces of an organism
that died long ago.
 Show that different
types of organisms
appeared at different
times and places on
Superposition – this principle states that if
the rock strata at a location have not been
disturbed, the lowest stratum was formed
before the strata above it.
Geologists put together a timeline for the
order in which different groups of rocks and
fossils were formed.
 The Geologic Time Scale
 Relative
age – its age compared to that of other
 Absolute age – more accurate using radiometric
Not all fossils are discovered and not all
remains become fossilized
Distribution of Fossils
Different organisms lived at different times
Today’s organisms are different from those of the past
Fossils found in adjacent layers are more like each
other than fossils found in deeper or higher layers.
4. By comparing fossils and rocks from around the
planet, we can infer when and where different
organisms existed.
5. Species have differed in a gradual sequence of forms
over time.
Biogeography, the geographic distribution of
species, suggested to Darwin that organisms
evolve from common ancestors
Darwin noted that animals on islands resemble
species on nearby mainland more closely than they
resemble animals on similar islands close to other
Copyright © 2009 Pearson Education, Inc.
Transitional Species
Have features that are
intermediate between
those of hypothesized
ancestors and later
descendant species.
Pakicetus (terrestrial)
Rhodocetus (predominantly aquatic)
Pelvis and Dorudon (fully aquatic)
hind limb
Pelvis and
hind limb
Balaena (recent whale ancestor)
Anatomy and Embryology
Homologous structures – anatomical structures
that occur in different species and that originated
by heredity from a structure in the most recent
common ancestor of the species.
Anatomy and Embryology
Analogous structures
have closely related
functions but do not
derive from the same
ancestral structure.
Anatomy and Embryology
Vestigial structures –
seem to serve no
function but that
resemble structures
with functional roles
in related organisms.
Anatomy and Embryology
The development of animal embryos is also
evidence of descent with modification
Chick embryo
Human embryo
Biological Molecules
Biologists can compare the DNA, RNA, proteins,
and other biological molecules from many
different organisms.
 They can then look for similarities and differences
among the data for each species
 The greater the number of similarities between
any given species, the more closely the species are
related through a common ancestor.