Transcript 25-Evolution

Lecture 25
Evolution
What is Evolution?
 Change over time, building on past & current features
 Products evolve
 Knowledge evolves
 Beliefs evolve
What is Evolution?
 In other cultures and religions,
for example Taoism, evolution
plays a central role
 Evolutionary patterns in biology
have been noted as far back as
Aristotle
 Darwin initially used the phrase
“descent with modification” to
explain the concept of evolution
 Patterns of biological evolution
have been observed in three
major areas:
 Fossil records
 Anatomical features
 Molecular distances
Evolution: Getting from There to Here
 Macroevolution
 Evolutionary change on a
grand scale
 Encompasses the origins of
new species and major
episodes of extinction
 Microevolution
 Evolutionary change on a
small scale
 Encompasses the genetic
changes that occur within
populations over time
 These changes are the result
of changes in gene
frequencies
Evolution: Getting from there to Here
 Prior to Darwin and Wallace it was
widely thought that biological evolution
occurred by inheritance of acquired
characteristics
 Individuals passed on to offspring body
and behavior changes acquired during
their lives
 In contrast, Darwin and Wallace
proposed that: variation is an inherent
characteristic of all biological
populations

It is not created by experience
 This is readily observable in all
populations – just look around this room
The Pace of Evolution
 The standard view since Darwin was that evolutionary change occurred
extremely slowly
 Imperceptible changes accumulate such that, over thousands or
millions of years, major changes could occur
 This is termed gradualism
 In 1972, Niles Eldredge and Stephen Jay Gould proposed the
Punctuated Equilibrium hypothesis
 Evolutionary change occurs in bursts separated by long periods of
little or no evolutionary change (termed stasis)
 Examples of both gradualism and punctuated equilibrium exist
 So speciation clearly occurs in different ways
 However, the idea that speciation is necessarily linked to phenotypic
change has not been supported
 Speciation can occur without phenotypic change
 Phenotypic change can occur within a species in the absence of speciation
The Rate of Evolution
 Different kinds of
organisms do evolve at
different rates
 Bacteria evolve much faster
than eukaryotes
 The rate of evolution also
differs within the same
group of species
 In punctuated equilibrium,
evolution occurs in spurts
 In gradualism, evolution
occurs in a gradual, uniform
way
The Evidence For Evolution
 Evidence for evolution comes from the following
 Fossil record
 Anatomical record
 Molecular record
Fossil Record
 Provides the most direct
evidence for
macroevolution
Large blunt
horns
 Fossils are the preserved
remains, tracks, or traces
of once-living organisms
 They form when
organisms become
buried in sediment and
calcium in hard surfaces
mineralizes
 Arraying fossils
according to age often
provides evidence of
successive evolutionary
change
Small bony
protuberance
Hoofed mammals
Evolution in the titanotheres
Fossil Record
 Fossils have been
found linking all the
major groups
 The forms linking
mammals to reptiles
are particularly well
known
Anatomical Record: Ontogeny
 Ontogeny Recapitulates Phylogeny
 All vertebrates share a basic set of developmental instructions
Anatomical Record: Homology
 Homologous structures
 Have different structure and function but are all derived from the
same part of a common ancestor
 A common ancestor possessed this 1-2-5 structure
 Adaptations to different environments modified this structure in
different ways
Anatomical Record: Analogy
 Analogous structures
 Resemble each other as
a result of parallel
evolutionary adaptations
to similar environments
Convergent evolution: many paths to one goal
 Analogous structures are the result of convergent evolution
 Different animals often adapt in similar fashion when challenged
by similar adversities or opportunities
Anatomical Record
 Vestigial organs
 Structures that are no longer
in use such as the human
appendix
 Apes have a much larger
appendix that is involved in
digestion
Molecular Record: Evolutionary Distance
 New alleles arise by
mutations and they come
to predominance through
favorable selection
 Thus, evolutionary
changes involve a
continual accumulation of
genetic changes
 Distantly-related
organisms accumulate a
greater number of
evolutionary differences
than closely-related ones
 This divergence is seen
among vertebrates in the
146-amino acid
hemoglobin b chain
Molecular Record: Molecular Clock
 This same pattern of
divergence is seen with DNA
sequences, such as that of
the cytochrome c gene
 The changes appear to
accumulate at a constant rate
 This phenomenon is referred
to as a molecular clock
Note: Different proteins evolve at different rates
Molecular Record: Homology

The eyes of these organisms are
NOT homologous

The genes controlling eye
development ARE homologous

500 million years ago an ancestor
evolved the “switch” for eye
development
 Probably simplest type of eye
structure
 1 pigment cell & 1 photoreceptor

The gene was passed on to all its
descendents

These descendents evolved
different types of complex eyes
 Each switched on by a
descendent of the original gene
Evolution’s Critics
 Critics of evolution raise seven principal objections
1.
2.
3.
4.
5.
6.
Evolution is not solidly demonstrated
There are no fossil intermediates
The intelligent design (irreducible complexity) argument
Evolution violates the 2nd law of thermodynamics
Proteins are too improbable
Natural selection does not imply evolution
None of these objections has held up to scientific scrutiny
Evolution & Religion
 “Today, almost half a century after the publication of the Encyclical, new
knowledge has led to the recognition of more than a hypothesis in the
theory of evolution.
 It is indeed remarkable that this theory has been progressively accepted
by researchers, following a series of discoveries in various fields of
knowledge.
 The convergence, neither sought nor fabricated, of the results of work
that was conducted independently is in itself a significant argument in
favor of the theory.”
Pope John Paul II
November 19, 1996
Address to the Pontifical Academy of Sciences
The Evolutionary Path to Apes
 The story of human evolution begins around 65 mya with the Archonta
 A group of small, arboreal mammals that were primarily insectivorous
 They underwent an explosive radiation that gave rise to different types of
mammals including bats and primates
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The Earliest Primates had two distinct
features that allowed them to succeed in the
arboreal insect-eating environment
 Grasping fingers and toes
 Allow them to grip limbs, hang from
branches & use tools
 Overlapping binocular vision
 Lets the brain judge distance
precisely
~ 40 mya, the earliest primates split into two
groups: Prosimians and Anthropoids
Prosimians (“before monkeys”)
 Primarily nocturnal and herbivorous
 Only a few survive today
Origin of the Anthropoids
 Higher primates include monkeys, apes and humans

Anthropoids are almost all
diurnal and herbivorous
 Evolved a bigger brain
and improved senses to
adapt to daytime foraging
 Live in groups with
complex social
interactions
 Tend to care for their
young for prolonged
periods of time

Early anthropoids, now
extinct, evolved in Africa
 Their direct descendants
are:
 Old World Monkeys
Stayed in Africa
Split into two lineages
i. Old world monkeys
ii. Hominoids
Many are ground dwellers
None have prehensile tails
 New World Monkeys
Migrated to South America
Developed in isolation
All are arboreal
Most have prehensile tails
Comparing Apes to Hominids
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Hominoids evolved from
anthropoids
 Apes
 Hominids (humans and their
direct ancestors)
Chimpanzees are the closest living
human relatives
 Chimpanzees and humans
share 98.4% of their
nuclear DNA
 Gorillas and humans share
about 97.7%
The common ancestor of apes and hominids is thought to have been an
arboreal climber
 Hominids became bipedal (walking upright)
 Apes evolved knuckle-walking
Anatomical differences between the two are related to bipedal locomotion
Considerable controversy exists about the identity of the first hominoid
 Attention is now focused on an early Miocene ape, Proconsul
 Has many of the characteristics of Old World Monkeys
 It lacks a tail and has apelike hands, feet and pelvis
A Hominid Evolutionary Tree

There are two major
groups of hominids
 The genus Homo
 3-7 species
depending on how
you count them
 The genus
Australopithecus
 7 species
 Older
 Smaller-brained

Australopithecine characteristics
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Bipedal
~ 1 m tall and ~ 18 kg in weight
Hominid dentition
Brains not any larger than those
of apes
 Fossils only found in Africa
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Bipedalism seems to have evolved as our
ancestors left dense forests for grasslands
and open woodland
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Did bipedalism precede or succeed brain
enlargement?
 Fossils unearthed in Africa demonstrate
that bipedalism extended back 4 mya
 Substantial brain expansion, on the other
hand, did not appear until about 2 mya
Out of Africa: Homo erectus

The first humans evolved from
australopithecine ancestors about 2
mya
 The exact ancestor is thought to be A.
afarensis

In the 1960s, hominid bones were
found near stone tools in Africa
 This early human was called Homo
habilis (Latin for “handy man”)
 It closely resembled Australopithecus
but had a larger brain
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In 1891, in Java, a Dutch anatomist
named Eugene Dubois found a
500,000 year old skull cap and
thighbone which he called Java man,
 The thigh bone indicated that he was
bipedal
 The skull indicated a brain twice the
size of that of Australopithecus
 Now recognized as Homo erectus:
Taller than H. habilis with a larger brain
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In 1976, a 1.5 million year old H.
erectus skull was found in East Africa
 This suggests that H. erectus originated
there and migrated into Asia and
Europe
 H. erectus survived for over a million
years - longer than any other species of
humans
The Last Stage of Hominid Evolution
 Modern humans first appeared in Africa about 600,000 years ago
 Three human species are thought to have evolved
 Homo heidelbergensis
 Evolved in Africa about 600,000 years ago
 Migrated to Europe and Western Asia
 Homo neanderthalensis
 Appeared in Europe about 130,000 years ago as H. heidelbergensis
was becoming rarer
 Likely branched off of the ancestral line leading to modern humans
 Homo sapiens (“wise man”)
 Evolved in Africa about 130,000 years ago then migrated to Europe
and Asia
 This is called the Recently-Out-of-Africa model
 This model is supported by a variety of gene studies
 Human mitochondrial DNA
 Y and X chromosomes
 Autosomes
Our Own Species: Homo sapiens

Neanderthals (H. neanderthalensis)
 Named after the Neander Valley of Germany
where their fossils were first discovered in 1856
 Evolved in Europe, then migrated to Asia
 Abruptly disappeared about 34,000 years ago

Cro-Magnons (H. sapiens)
 Named after the Valley in France where their
fossils were first discovered
 Evolved in Africa, then migrated to Asia
 Eventually spread to N. America and Australia
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We humans are unique animals and the product
of evolution
 Our evolution has been marked by a progressive
increase in brain size
 Refined and extended conceptual thought
 Symbolic language
 Cultural evolution