Speciation occurs through the formation of new species via the splitting of existing species. Species are created through a series of evolutionary processes where populations become isolated from each other due to barriers like geographic separation. Isolated populations then evolve independently, developing characteristics that prevent interbreeding if they come into contact again, resulting in reproductive isolation and the formation of new species.

1. AIM: How do new species arise?
Warm – up:
How does artificial
selection resemble
natural selection?

2. The Origin of Species
Mom, Dad…
There’s something
you need to know…
I’m a MAMMAL!

3. “That mystery of mysteries…”

4. “That mystery of mysteries…”
Darwin never actually tackled
how new species arose…

5. “That mystery of mysteries…”
Darwin never actually tackled
how new species arose…
Both in space and time,
we seem to be brought
somewhat near to that great fact
—that mystery of mysteries—
the first appearance of
new beings on this Earth.

6. So…what is a species?

7. So…what is a species?
§ Biological species concept

8. So…what is a species?
§ Biological species concept
u population whose members can
interbreed & produce viable, fertile
offspring

9. So…what is a species?
§ Biological species concept
u population whose members can
interbreed & produce viable, fertile
offspring
u reproductively compatible

10. So…what is a species?
§ Biological species concept
u population whose members can
interbreed & produce viable, fertile
offspring
u reproductively compatible
Eastern Meadowlark Western Meadowlark

11. So…what is a species?
§ Biological species concept
u population whose members can
interbreed & produce viable, fertile
offspring
u reproductively compatible
Distinct species:
songs & behaviors are different
enough to prevent interbreeding
Eastern Meadowlark Western Meadowlark

12. How and why do new species originate?

13. How and why do new species originate?
§ Speciation: formation of a new species by the
splitting of an existing species

14. How and why do new species originate?
§ Speciation: formation of a new species by the
splitting of an existing species
§ Species are created by a series of
evolutionary processes

15. How and why do new species originate?
§ Speciation: formation of a new species by the
splitting of an existing species
§ Species are created by a series of
evolutionary processes
u populations become isolated due to various
isolating mechanisms

16. How and why do new species originate?
§ Speciation: formation of a new species by the
splitting of an existing species
§ Species are created by a series of
evolutionary processes
u populations become isolated due to various
isolating mechanisms
§ geographically isolated

17. How and why do new species originate?
§ Speciation: formation of a new species by the
splitting of an existing species
§ Species are created by a series of
evolutionary processes
u populations become isolated due to various
isolating mechanisms
§ geographically isolated
§ reproductively isolated, etc.

18. How and why do new species originate?
§ Speciation: formation of a new species by the
splitting of an existing species
§ Species are created by a series of
evolutionary processes
u populations become isolated due to various
isolating mechanisms
§ geographically isolated
§ reproductively isolated, etc.
u isolated populations
evolve independently

19. How and why do new species originate?
§ Speciation: formation of a new species by the
splitting of an existing species
§ Species are created by a series of
evolutionary processes
u populations become isolated due to various
isolating mechanisms
§ geographically isolated
§ reproductively isolated, etc.
u isolated populations
evolve independently
§ Isolation

20. How and why do new species originate?
§ Speciation: formation of a new species by the
splitting of an existing species
§ Species are created by a series of
evolutionary processes
u populations become isolated due to various
isolating mechanisms
§ geographically isolated
§ reproductively isolated, etc.
u isolated populations
evolve independently
§ Isolation
u allopatric

21. How and why do new species originate?
§ Speciation: formation of a new species by the
splitting of an existing species
§ Species are created by a series of
evolutionary processes
u populations become isolated due to various
isolating mechanisms
§ geographically isolated
§ reproductively isolated, etc.
u isolated populations
evolve independently
§ Isolation
u allopatric
§ geographic separation

22. How and why do new species originate?
§ Speciation: formation of a new species by the
splitting of an existing species
§ Species are created by a series of
evolutionary processes
u populations become isolated due to various
isolating mechanisms
§ geographically isolated
§ reproductively isolated, etc.
u isolated populations
evolve independently
§ Isolation
u allopatric
§ geographic separation
u sympatric

23. How and why do new species originate?
§ Speciation: formation of a new species by the
splitting of an existing species
§ Species are created by a series of
evolutionary processes
u populations become isolated due to various
isolating mechanisms
§ geographically isolated
§ reproductively isolated, etc.
u isolated populations
evolve independently
§ Isolation
u allopatric
§ geographic separation
u sympatric
§ still live in same area

24. Pre-reproduction barriers
§ Obstacle to mating or to fertilization if
mating occurs

25. Pre-reproduction barriers
§ Obstacle to mating or to fertilization if
mating occurs
geographic isolation

26. Pre-reproduction barriers
§ Obstacle to mating or to fertilization if
mating occurs
geographic isolation ecological isolation

27. Pre-reproduction barriers
§ Obstacle to mating or to fertilization if
mating occurs
geographic isolation ecological isolation temporal isolation

28. Pre-reproduction barriers
§ Obstacle to mating or to fertilization if
mating occurs
geographic isolation ecological isolation temporal isolation
behavioral isolation

29. Pre-reproduction barriers
§ Obstacle to mating or to fertilization if
mating occurs
geographic isolation ecological isolation temporal isolation
behavioral isolation mechanical isolation

30. Pre-reproduction barriers
§ Obstacle to mating or to fertilization if
mating occurs
geographic isolation ecological isolation temporal isolation
behavioral isolation mechanical isolation gametic isolation

31. Ammospermophilus spp
Geographic isolation

32. Ammospermophilus spp
Geographic isolation
§ Species occur in different areas

33. Ammospermophilus spp
Geographic isolation
§ Species occur in different areas
u physical barrier

34. Ammospermophilus spp
Geographic isolation
§ Species occur in different areas
u physical barrier
u allopatric speciation

35. Ammospermophilus spp
Geographic isolation
§ Species occur in different areas
u physical barrier
u allopatric speciation
§ “other country”
Harris’s antelope
squirrel inhabits
the canyon’s
south rim (L). Just
a few miles away
on the north rim
(R) lives the
closely related
white-tailed
antelope squirrel

37. • Within each population there are
breeding subunits called demes

38. • Within each population there are
breeding subunits called demes
• Individuals within a deme tend to
breed with each other more
often than with members of
other demes.

39. • Within each population there are
breeding subunits called demes
• Individuals within a deme tend to
breed with each other more
often than with members of
other demes.
• They remain part of the same gene pool, but
…gene flow between separate demes slows, and…
… may even stop.

40. • Within each population there are
breeding subunits called demes
• Individuals within a deme tend to
breed with each other more
often than with members of
other demes.
• They remain part of the same gene pool, but
…gene flow between separate demes slows, and…
… may even stop.
• Each deme may evolve along separate lines, so…
…when reunited they may no longer be able to
interbreed

41. Speciation may occur where different parts of a
population of a species become isolated from
one another.

42. Speciation may occur where different parts of a
population of a species become isolated from
one another.
Example: a species of butterfly is widely distributed
across an area of grassland.

43. Speciation may occur where different parts of a
population of a species become isolated from
one another.
Example: a species of butterfly is widely distributed
across an area of grassland.

44. Climate changes
cause the area to
become wetter…

45. Climate changes
cause the area to
become wetter…

46. Climate changes
cause the area to
become wetter… …and a river forms

47. Climate changes
cause the area to
become wetter… …and a river forms
Because the
butterflies are not
strong fliers…

48. Climate changes
cause the area to
become wetter… …and a river forms
Because the
butterflies are not
strong fliers… …they cannot cross the
river

49. Climate changes
cause the area to
become wetter… …and a river forms
Because the
butterflies are not
strong fliers… …they cannot cross the
river
The two groups of butterflies are now isolated from
each other

50. One side of the
river remains as
grassland

51. One side of the
river remains as
grassland
The other side
develops into
woodland

52. The selective
pressures are different
on either side of the
river, so…

53. The selective
pressures are different
on either side of the
river, so…
…the two populations
evolve different wing
patterns

54. NOTE: At this stage
the two populations
may not be different
enough to be
considered as two
separate species…

55. NOTE: At this stage
the two populations
may not be different
enough to be
considered as two
separate species…
…they may be considered
as subspecies or varieties.

56. The climate changes
again and becomes
drier

57. The climate changes
again and becomes
drier
The river barrier is lost

58. The climate changes
again and becomes
drier
The river barrier is lost
The land becomes mainly
grassland

59. The two populations of
butterfly can now mix
together, but…

60. The two populations of
butterfly can now mix
together, but…
…successful mating requires that they
recognise each other by wing pattern, so…

61. The two populations of
butterfly can now mix
together, but…
…successful mating requires that they
recognise each other by wing pattern, so…
…they do not interbreed.

62. The two populations of
butterfly can now mix
together, but…
…successful mating requires that they
recognise each other by wing pattern, so…
…they do not interbreed.
The two populations are now definitely different species.

63. Allopatric Speciation

64. Allopatric Speciation
Demes are separated by …
… a physical
barrier

65. Allopatric Speciation
Demes are separated by …
… a physical
barrier
‘Allopatric’ means … … ‘different
fatherland’

66. Sympatric Speciation

67. Sympatric Speciation
•Speciation which occurs when some factor (other
than geographic barriers) prevents two populations
living in the same area from interbreeding

68. Sympatric Speciation
•Speciation which occurs when some factor (other
than geographic barriers) prevents two populations
living in the same area from interbreeding
•‘Sympatric’ means ‘same fatherland’

69. Ecological isolation
§ Species occur in same area, but occupy
different habitats so rarely encounter
each other

70. Ecological isolation
§ Species occur in same area, but occupy
different habitats so rarely encounter
each other
2 species of garter snake, Thamnophis,
occur in same area, but one lives in water &
other is terrestrial

71. Ecological isolation
§ Species occur in same area, but occupy
different habitats so rarely encounter
each other
2 species of garter snake, Thamnophis,
occur in same area, but one lives in water &
other is terrestrial
lions & tigers could
hybridize, but they
live in different
habitats:
§ lions in grasslands
§ tigers in rainforest

72. Temporal isolation
§ Species that breed during different
times of day, different seasons, or
different years cannot mix gametes
u sympatric speciation
§ “same country”

73. Temporal isolation
§ Species that breed during different
times of day, different seasons, or
different years cannot mix gametes
u sympatric speciation
§ “same country”
Eastern spotted skunk
(L) & western spotted
skunk (R) overlap in
range but eastern mates
in late winter & western
mates in late summer

74. sympatric speciation?
Behavioral isolation
Blue footed boobies mate
only after a courtship display
unique to their species

75. sympatric speciation?
Behavioral isolation
§ Unique behavioral patterns & rituals isolate species
Blue footed boobies mate
only after a courtship display
unique to their species

76. sympatric speciation?
Behavioral isolation
§ Unique behavioral patterns & rituals isolate species
u identifies members of species
Blue footed boobies mate
only after a courtship display
unique to their species

77. sympatric speciation?
Behavioral isolation
§ Unique behavioral patterns & rituals isolate species
u identifies members of species
u attract mates of same species 
Blue footed boobies mate
only after a courtship display
unique to their species

78. sympatric speciation?
Behavioral isolation
§ Unique behavioral patterns & rituals isolate species
u identifies members of species
u attract mates of same species 
§ courtship rituals, mating calls
Blue footed boobies mate
only after a courtship display
unique to their species

79. Recognizing your
own species

80. Recognizing your
own species
courtship display of
Gray-Crowned Cranes, Kenya

81. Recognizing your
own species
courtship display of
Gray-Crowned Cranes, Kenya
What can you say?

82. Recognizing your
own species
courtship songs of sympatric
species of lacewings
courtship display of
Gray-Crowned Cranes, Kenya
firefly courtship displays

83. Sympatric speciation: Example 1

84. Sympatric speciation: Example 1
Chiffchaff Willow warbler
(Phylloscopus (Phylloscopus trochilus)
collybita)

85. Sympatric speciation: Example 1
Chiffchaff Willow warbler
(Phylloscopus (Phylloscopus trochilus)
collybita)
Two small insect-eating birds
which spend summer in Britain

86. Sympatric speciation: Example 1
Chiffchaff Willow warbler
(Phylloscopus (Phylloscopus trochilus)
collybita)
Two small insect-eating birds
which spend summer in Britain
They are difficult to tell apart by their appearance.

87. For both species,
their songs are an important part of courtship
Willow warbler Chiffchaff

88. For both species,
their songs are an important part of courtship
Willow warbler Chiffchaff
Their songs are
very different

89. For both species,
their songs are an important part of courtship
Willow warbler Chiffchaff
Their songs are
very different
Successful mating will only result from the correct
behaviour pattern, so…

90. For both species,
their songs are an important part of courtship
Willow warbler Chiffchaff
Their songs are
very different
Successful mating will only result from the correct
behaviour pattern, so…
… willow warblers and chiffchaffs do not interbreed

91. Example 3: Production of Infertile Hybrids

92. Example 3: Production of Infertile Hybrids

93. Example 3: Production of Infertile Hybrids
Carrion crow
(Corvus corone)

94. Example 3: Production of Infertile Hybrids
Carrion crow
(Corvus corone)

95. Example 3: Production of Infertile Hybrids
Carrion crow Hooded crow
(Corvus corone) (Corvus cornix)

96. Example 3: Production of Infertile Hybrids
Carrion crow Hooded crow
(Corvus corone) (Corvus cornix)
Found in England, Found in Northern
Wales and Scotland and
Southern Scotland Ireland

97. Carrion crow Hooded crow

98. Carrion crow Hooded crow
Territories of the
two species do
overlap slightly,
so…

99. Carrion crow Hooded crow
Territories of the
two species do
overlap slightly,
so…
… carrion crows and hooded crows do interbreed to
produce hybrids, but…

100. Carrion crow Hooded crow
Territories of the
two species do
overlap slightly,
so…
… carrion crows and hooded crows do interbreed to
produce hybrids, but…
… hybrids are not as fertile as the parents, so…

101. Carrion crow Hooded crow
Territories of the
two species do
overlap slightly,
so…
… carrion crows and hooded crows do interbreed to
produce hybrids, but…
… hybrids are not as fertile as the parents, so…
… selection favours the parents.

102. sympatric speciation?
Mechanical isolation
§ Morphological differences can prevent
successful mating
Plants

103. sympatric speciation?
Mechanical isolation
§ Morphological differences can prevent
successful mating
Plants
Even in closely related
species of plants, the
flowers often have distinct
appearances that attract
different pollinators.
These 2 species of monkey
flower differ greatly in
shape & color, therefore
cross-pollination does not
happen.

104. Example 2: Failure to transfer gametes

105. Example 2: Failure to transfer gametes
Corn poppy
(Papaver rhoeas)

106. Example 2: Failure to transfer gametes
Corn poppies are
pollinated by…
Corn poppy
(Papaver rhoeas)

107. Example 2: Failure to transfer gametes
Corn poppies are
pollinated by…
Corn poppy
(Papaver rhoeas) … bees

108. Bees can distinguish between corn poppies and other
species of poppy.

109. Bees can distinguish between corn poppies and other
species of poppy.
Papaver alpinum Papaver orientale Papaver somniferum
Bees visiting one species will not visit another
species, so…

110. Bees can distinguish between corn poppies and other
species of poppy.
Papaver alpinum Papaver orientale Papaver somniferum
Bees visiting one species will not visit another
species, so…
…pollen is not transferred between species and
interbreeding does not occur.

111. Mechanical isolation Animals
Damsel fly penises

112. Mechanical isolation Animals
§ For many insects, male &
female sex organs of
closely related species do
not fit together, preventing
sperm transfer
Damsel fly penises

113. Mechanical isolation Animals
§ For many insects, male &
female sex organs of
closely related species do
not fit together, preventing
sperm transfer
u lack of “fit” between sexual organs:
hard to imagine for us… but a big issue for insects with
different shaped genitals!
Damsel fly penises

114. Mechanical isolation Animals
§ For many insects, male &
female sex organs of
closely related species do
not fit together, preventing
sperm transfer
u lack of “fit” between sexual organs:
hard to imagine for us… but a big issue for insects with
different shaped genitals!
I can’t even imagine!
Damsel fly penises

115. sympatric speciation?
Gametic isolation

116. sympatric speciation?
Gametic isolation
Sea urchins release sperm
& eggs into surrounding
waters where they fuse &
form zygotes. Gametes of
different species— red &
purple —are unable to fuse.

117. sympatric speciation?
Gametic isolation
§ Sperm of one species may not be able to fertilize
eggs of another species
Sea urchins release sperm
& eggs into surrounding
waters where they fuse &
form zygotes. Gametes of
different species— red &
purple —are unable to fuse.

118. sympatric speciation?
Gametic isolation
§ Sperm of one species may not be able to fertilize
eggs of another species
u mechanisms
Sea urchins release sperm
& eggs into surrounding
waters where they fuse &
form zygotes. Gametes of
different species— red &
purple —are unable to fuse.

119. sympatric speciation?
Gametic isolation
§ Sperm of one species may not be able to fertilize
eggs of another species
u mechanisms
§ biochemical barrier so sperm cannot penetrate egg
Sea urchins release sperm
& eggs into surrounding
waters where they fuse &
form zygotes. Gametes of
different species— red &
purple —are unable to fuse.

120. sympatric speciation?
Gametic isolation
§ Sperm of one species may not be able to fertilize
eggs of another species
u mechanisms
§ biochemical barrier so sperm cannot penetrate egg
w receptor recognition: lock & key between egg & sperm
Sea urchins release sperm
& eggs into surrounding
waters where they fuse &
form zygotes. Gametes of
different species— red &
purple —are unable to fuse.

121. sympatric speciation?
Gametic isolation
§ Sperm of one species may not be able to fertilize
eggs of another species
u mechanisms
§ biochemical barrier so sperm cannot penetrate egg
w receptor recognition: lock & key between egg & sperm
§ chemical incompatibility
Sea urchins release sperm
& eggs into surrounding
waters where they fuse &
form zygotes. Gametes of
different species— red &
purple —are unable to fuse.

122. sympatric speciation?
Gametic isolation
§ Sperm of one species may not be able to fertilize
eggs of another species
u mechanisms
§ biochemical barrier so sperm cannot penetrate egg
w receptor recognition: lock & key between egg & sperm
§ chemical incompatibility
w sperm cannot survive in female reproductive tract
Sea urchins release sperm
& eggs into surrounding
waters where they fuse &
form zygotes. Gametes of
different species— red &
purple —are unable to fuse.

123. Post-reproduction barriers
zebroid

124. Post-reproduction barriers
§ Prevent hybrid offspring from
developing into a viable, fertile adult
zebroid

125. Post-reproduction barriers
§ Prevent hybrid offspring from
developing into a viable, fertile adult
u reduced hybrid viability
zebroid

126. Post-reproduction barriers
§ Prevent hybrid offspring from
developing into a viable, fertile adult
u reduced hybrid viability
u reduced hybrid fertility
zebroid

127. Post-reproduction barriers
§ Prevent hybrid offspring from
developing into a viable, fertile adult
u reduced hybrid viability
u reduced hybrid fertility
u hybrid breakdown
zebroid

128. sympatric speciation?
Reduced hybrid viability
§ Genes of different parent species may
interact & impair the hybrid’s development

129. sympatric speciation?
Reduced hybrid viability
§ Genes of different parent species may
interact & impair the hybrid’s development
Species of salamander
genus, Ensatina, may
interbreed, but most
hybrids do not complete
development & those
that do are frail.

130. Reduced hybrid fertility

131. Reduced hybrid fertility
§ Even if hybrids are vigorous
they may be sterile

132. Reduced hybrid fertility
§ Even if hybrids are vigorous
they may be sterile
u chromosomes of parents may differ in number
or structure & meiosis in hybrids may fail to
produce normal gametes

133. Reduced hybrid fertility
§ Even if hybrids are vigorous
they may be sterile
u chromosomes of parents may differ in number
or structure & meiosis in hybrids may fail to
produce normal gametes

134. Reduced hybrid fertility
§ Even if hybrids are vigorous
they may be sterile
u chromosomes of parents may differ in number
or structure & meiosis in hybrids may fail to
produce normal gametes

135. Reduced hybrid fertility
§ Even if hybrids are vigorous
they may be sterile
u chromosomes of parents may differ in number
or structure & meiosis in hybrids may fail to
produce normal gametes
Mules are vigorous,
but sterile

136. Reduced hybrid fertility
§ Even if hybrids are vigorous
they may be sterile
u chromosomes of parents may differ in number
or structure & meiosis in hybrids may fail to
produce normal gametes
Mules are vigorous,
but sterile
Horses have 64
chromosomes
(32 pairs)

137. Reduced hybrid fertility
§ Even if hybrids are vigorous
they may be sterile
u chromosomes of parents may differ in number
or structure & meiosis in hybrids may fail to
produce normal gametes
Mules are vigorous,
but sterile
Horses have 64 Donkeys have 62
chromosomes chromosomes
(32 pairs) (31 pairs)

138. Reduced hybrid fertility
§ Even if hybrids are vigorous
they may be sterile
u chromosomes of parents may differ in number
or structure & meiosis in hybrids may fail to
produce normal gametes
Mules are vigorous,
but sterile
Horses have 64 Donkeys have 62
chromosomes chromosomes
(32 pairs) Mules have 63 chromosomes! (31 pairs)

139. Reduced hybrid fertility
§ Even if hybrids are vigorous
they may be sterile
u chromosomes of parents may differ in number
or structure & meiosis in hybrids may fail to
produce normal gametes
Mules are vigorous,
but sterile
Horses have 64 Donkeys have 62
chromosomes chromosomes
(32 pairs) Mules have 63 chromosomes! (31 pairs)

140. Reduced hybrid fertility
§ Even if hybrids are vigorous
they may be sterile
u chromosomes of parents may differ in number
or structure & meiosis in hybrids may fail to
produce normal gametes
Mules are vigorous,
but sterile
Horses have 64 Donkeys have 62
chromosomes chromosomes
(32 pairs) Mules have 63 chromosomes! (31 pairs)

141. Reduced hybrid fertility
§ Even if hybrids are vigorous
they may be sterile
u chromosomes of parents may differ in number
or structure & meiosis in hybrids may fail to
produce normal gametes
Mules are vigorous,
but sterile
Horses have 64 Donkeys have 62
chromosomes chromosomes
(32 pairs) Mules have 63 chromosomes! (31 pairs)

142. sympatric speciation?
Hybrid breakdown
§ Hybrids may be fertile & viable in first
generation, but when they mate offspring
are feeble or sterile

143. sympatric speciation?
Hybrid breakdown
§ Hybrids may be fertile & viable in first
generation, but when they mate offspring
are feeble or sterile
In strains of cultivated rice,
hybrids are vigorous but
plants in next generation are
small & sterile.
On path to separate species.

144. Speciation through Polyploidy
§ Polyploidy results from failed meiosis
which leads to an organism that has
two sets of chromosomes.
§ Polyploid types are labelled according
to the number of chromosome sets in
the nucleus
ex. Tetraploid, hexaploid, etc.

145. Polyploidy
§ Most common in plants because they are able
to self-fertilize
§ 2n + 2n = 4n
§ Most polyploids display heterosis relative to
their parental species, and may display
variation or morphologies that may contribute
to the process of speciation
§ Polyploid plants, even though they are sterile
can reproduce vegetatively. Through chance,
the chromosome number may double again,
making it fertile again…and therefore a new
species!

146. Rate of Speciation
Niles Eldredge
Curator
American Museum of Natural History

147. Rate of Speciation
§ Current debate:
Niles Eldredge
Curator
American Museum of Natural History

148. Rate of Speciation
§ Current debate:
Does speciation happen gradually or
rapidly
Niles Eldredge
Curator
American Museum of Natural History

149. Rate of Speciation
§ Current debate:
Does speciation happen gradually or
rapidly
u Gradualism
Niles Eldredge
Curator
American Museum of Natural History

150. Rate of Speciation
§ Current debate:
Does speciation happen gradually or
rapidly
u Gradualism
§ Charles Darwin
Niles Eldredge
Curator
American Museum of Natural History

151. Rate of Speciation
§ Current debate:
Does speciation happen gradually or
rapidly
u Gradualism
§ Charles Darwin
§ Charles Lyell
Niles Eldredge
Curator
American Museum of Natural History

152. Rate of Speciation
§ Current debate:
Does speciation happen gradually or
rapidly
u Gradualism
§ Charles Darwin
§ Charles Lyell
u Punctuated equilibrium
Niles Eldredge
Curator
American Museum of Natural History

153. Rate of Speciation
§ Current debate:
Does speciation happen gradually or
rapidly
u Gradualism
§ Charles Darwin
§ Charles Lyell
u Punctuated equilibrium
§ Stephen Jay Gould
Niles Eldredge
Curator
American Museum of Natural History

154. Rate of Speciation
§ Current debate:
Does speciation happen gradually or
rapidly
u Gradualism
§ Charles Darwin
§ Charles Lyell
u Punctuated equilibrium
§ Stephen Jay Gould
§ Niles Eldredge
Niles Eldredge
Curator
American Museum of Natural History

155. Gradualism

156. Gradualism
§ Slow change from
one form to another

157. Gradualism
§ Slow change from
one form to another
§ Gradual divergence
over long spans of
time

158. Gradualism
§ Slow change from
one form to another
§ Gradual divergence
over long spans of
time
u assume that big
changes occur as
the accumulation
of many small ones

159. Punctuated Equilibrium
Time

160. Punctuated Equilibrium
§ Rate of speciation is
not constant
Time

161. Punctuated Equilibrium
§ Rate of speciation is
not constant
u rapid bursts of
change
Time

162. Punctuated Equilibrium
§ Rate of speciation is
not constant
u rapid bursts of
change
u long periods of little
or no change
Time

163. Punctuated Equilibrium
§ Rate of speciation is
not constant
u rapid bursts of
change
u long periods of little
or no change
u species undergo
rapid change when
they 1st bud from
parent population
Time

164. Stephen Jay Gould (1941-2002)
§ Harvard paleontologist &
evolutionary biologist
u punctuated equilibrium
u prolific author
§ popularized evolutionary thought

165. Evolution is not goal-oriented

166. Evolution is not goal-oriented
An evolutionary trend does not mean that
evolution is goal-oriented.

167. Evolution is not goal-oriented
An evolutionary trend does not mean that
evolution is goal-oriented.

168. Evolution is not goal-oriented
An evolutionary trend does not mean that
evolution is goal-oriented.
Surviving species
do not represent
the peak of
perfection. There
is compromise &
random chance
involved as well

169. Evolution is not goal-oriented
An evolutionary trend does not mean that
evolution is goal-oriented.
Surviving species
do not represent
the peak of
perfection. There
is compromise &
random chance
involved as well

170. Evolution is not goal-oriented
An evolutionary trend does not mean that
evolution is goal-oriented.
Surviving species
do not represent
the peak of
perfection. There
is compromise &
random chance
involved as well
Remember that for
humans as well!

171. Any Questions??