Your Distant Past

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Your Distant Past

• Chapter 8

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Evidence for Evolution

• Fossil record
• Comparative Anatomy
• Developmental Biology
• Molecular Biology

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Charles Darwin
Alfred Russell Wallace

• The earth and life are very old
• Significant changes have occurred in both in the
  earth structure and in living organisms
• Some kind of natural process has played a role in
  producing the diversity of species

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• The finches on the Galapagos islands were
  different than the finches on the mainland of
  South America
• The animals of Indonesia were different than the
  animals of Malaysia and Borneo
• Did God arbitrarily place different animals on
  different lands?
• Can the distribution of different animals be
  explained by natural processes? Nature?

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What did Darwin and Wallace Say?

• Species change through time
• Organisms evolve

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What did Darwin and Wallace Say?

• Principle of variation
• Organisms of the same species are different from
  one another
• Principle of heredity
• Some of the differences are inherited
• Each species has the tendency to produce more
  offspring than the environment can support
• Individuals that are better adapted to their
  environment will produce more offspring
  (reproductive success)
• Principle of natural selection
• Organisms that experience the most reproductive
  success will produce more offspring than other
  individuals in the population. Their heritable
  traits will appear more often across successive
  generations
• Descent with modification natural selection
  acting on enough traits across a sufficient
  number of generations can produce a new species

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A Closer Look at Natural Selection

• 1928 Sir Alexander Fleming observed that the mold
  Penicillium kills the bacterium Staphlococcus
• 1939 researchers at Oxford isolated the
  antibiotic penicillin from the mold Penicillium
• 1941 large production of penicillin

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Selective Breeding among Cabbages
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Based on the artificial selection (selective
breeding) practiced by plant breeders

• If man can, by patience select variations
  useful to him, why, under the changing and
  complex conditions of life, should not variations
  useful to natures living products often arise,
  be preserved and selected?

The action of environment takes the place of
human choice.
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Natural Selection of Antibiotic Resistant Bacteria

• Principle of variation
• Organisms of the same species are different from
  one another
• Principle of heredity
• Individuals that are better adapted to their
  environment will produce more offspring
  (reproductive success)
• Principle of natural selection
• Organisms that experience the most reproductive
  success will produce more offspring than other
  individuals in the population. Their heritable
  traits will appear more often across successive
  generations
• Descent with modification natural selection
  acting on enough traits across a sufficient
  number of generations can produce a new species

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The Modern Synthesis (1900s)

• Random mutations and other genetic processes
  produce variation in nature genotypes
• Natural selection acts on the expressed
  phenotypes of the individual

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• Natural selection occurs in a population across
  time
• It increases the frequency of more fit
  phenotypes and decreases the phenotypes of less
  fit individuals
• Selection happens to individuals
• survival of the fittest leads to reproductive
  success
• Evolution happens to a population
• An individual must be part of a population to
  reproduce
• The genetic composition of a population changes
  as the proportion of individuals with specific
  genotypes changes

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Natural Selection
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Basics About Natural SelectionSickle Cell Anemia
Hemoglobin S
Hemoglobin (s)
DNA TGT GGG CTC CTC
DNA TGT GGG CAC CTC
Amino acids thr- pro-glu-glu
Amino acids thr- pro-val-glu
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Inheritance of Sickle Cell Anemia
Sickle cell gene s
Normal globin geneS
Aa
AA
Aa
Aa
aa
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Distribution of Malaria
The frequency of s allele in the human
population
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Sickle cells protect against malaria

• Tropical Africa
• Eastern Mediterranean
• Arabian Peninsula
• India
• People who carry one copy of the gene have a
  selective advantage in areas where Malaria is
  prevalent.
• Natural selection favors carriers of the
  hemoglobin s gene and so the frequency of the
  sickle cell gene in these populations is high.

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Predator/Prey Activity

• Best predator in the forest and the prairie?
• Most successful prey in the forest and prairie?
• How will natural selection change the species
  composition in these two environments?

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Descent With ModificationThe Big Picture

• Small scale changes in a population is
  microevolution
• How do species evolve? Macroevolution

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The Origin of Evolutionary Novelty

• Microevolution
• Blue eye color
• Rise and spread of sickle cell anemia
• Bird species splitting into two sister species

• Macroevolution
• Evolution of Vision
• Evolution of the circulatory system
• The evolution of several genera of bird species

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• Evidence that Macroevolution has occurred
• The Fossil record
• Fossils are actual remains or impressions of an
  organisms from a past geological age that have
  been preserved in the earths crust

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The Fossil Record

• Traces (Impressions)
• Fossilized Bones
• Ice, Bogs, Resins

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Woolly mammoth unearthed in Siberia

• Ice is an excellent preservative
• Mammoth preserved in ice for over 25,000 years
• Allows for DNA analysis

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• The fossil record reveals that an enormous
  diversity of life has existed on earth
• New species have emerged as others have gone
  extinct
• Paleontologists estimate that 99 of all species
  that ever lived on earth have gone extinct

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• Radioactive Dating tell scientist the age of a
  fossil
• Bacteria 3.5 bya
• Eukaryotic cells 1.7 bya
• Multicellular plants and animals 500 700 mya
• Birds and Mammals 200 mya
• Humans 5 mya

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The Evolution of Whales
Sometimes the evolution of an organism can be
reflected in the fossil record. Most of the time
the fossil record is incomplete.
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Descent with Modification

• What is the evidence that the different life
  forms as seen in the fossil record and existing
  today are related?
• Some of the evidence comes from Comparative
  Anatomy
• Comparing the similarities and differences in the
  anatomy of different species.

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Organisms with a suite of similar features tend
to be related by descent
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A Cat is a Cat
Felidae The Cat family
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The Evolution of Wings
Analogous Structures
Just because organisms look similar, it doesnt
mean they are related or share the same
evolutionary heritage.
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• Adaptations allow an organism to survive in a new
  environment
• Adaptations are not necessarily evidence that
  organisms are evolutionarily related

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Homologous structures

• Homologous structures do not necessarily look
  alike
• They are the same organ that has been modified
  for different adaptations

Descent with modification
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• Analogous structures are fundamentally different
  structures adapted to the same ecological niche
• evolution of wings (ability to fly)
• evolution of fins (ability to swim)
• Homologous structures represent the same
  structure adapted to different ecological niches
• modification of the forearm for flight, swimming
  and walking
• All mammals have 7 neck bones (giraffe, human,
  whale)

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• Evolution rarely results in the creation of an
  entirely new structure, instead evolution
  proceeds by modification of existing structures
• This is what Darwin meant by Descent with
  modification

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DNA Sequence Descent with Modification
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How do Species Form?

• Descent with modificationbut how?
• Natural selection explains both changes within a
  population and how species evolve

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What is a Species?

• Naming species
• Common names vs scientific name

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Canis lupus familiaris
Do all individuals of a species look alike?
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Horses, Donkeys, Mules
Horse X Donkey Mule
Do all individuals of a species look alike?
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What is a species?

• Any group of organisms that can interbreed in
  nature and produce fertile offspring
• Reproduction is essential
• Biological Species Concept Reproductive
  isolation leads to new species

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Barriers leading to Reproductive Isolation

• Geographic
• habitat
• Behavior
• Timing
• Mechanical
• Gametes

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Geographic Isolation
Liger
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Geographic Isolation Leading to Reproductive
Isolation
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What Barriers Cause Geographic Isolation?

• Depends on the size / type of organism
• Mountain building
• Rise and fall of sea levels either submerges or
  exposes land
• New rivers and streams

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• Barriers lead to geographic isolation
• The organisms are prevented from breeding with
  each other
• Mutations accumulate and lead to genetic
  differences between the two isolated populations
• They become a separate species when they can no
  longer breed

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Macroevolution

• The evolution of mammals from mammal-like
  reptilian ancestors is one of the best examples
  we have of macroevolution
• How did the Age of Reptiles give way to the
  Age of Mammals?
• A catastrophic event (?) destroyed most of the
  reptiles and since then they have been replaced
  by mammals

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Cretaceous Extinction65 mya

• The fossil record shows that large groups of
  animals periodically disappear from the earth
• AND are subsequently replaced by new organisms

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The New Features of Mammals

• Modified jaws
• Differentiation of teeth
• Endothermic
• Active metabolism (efficient respiratory and
  circulatory systems)
• Diaphram (aids in breathing)
• Hair (made of keratin) and a layer of fat tissue
  aid in retaining heat

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Macroevolution and Adaptive Radiation

• Changes in mammals evolved over a long period of
  time
• As mammals migrated to different environments,
  they evolved into new species
• Today mammals are the most successful
  vertebrates
• (Insects are the most successful animals)

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Natural Selection and the Evolution of Humans

• Characteristics of Primates
• Grasping feet or hands with opposable thumbs or
  toes
• Leg-dominated movement
• Front-facing eyes with stereoscopic vision
• Diminished sense of smell
• Large brains

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Primate Evolution
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Hominid Evolution

• Reconstructed from
• Fossilized bone
• Footprints (trace fossils)
• Cultural artifacts
• DNA sequence data

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What events and environmental conditions lead to
the evolution of humans?

• Bipedalism the ability to walk on two feet was
  the first significant event
• Structure of teeth and jaws
• Invention of tools
• Brain size

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Walking on Two feet
Human
Gorilla
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• A change in DIET altered teeth and jaw structure
• A change in BRAIN SIZE reflects cultural and
  social changes

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Australopithecus afarensis

• LUCY
• African origin
• One meter tall, head the size of a soft ball
• Bipedalism
• Large canine teeth
• 3-4 mya

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Homo habilis

• Homo habilis appears 2.5 mya
• Bipedalism first, then larger brains
• Handy man
• Sharp-edged flakes and stones used for cutting
  and grinding food
• Coexisted for one million years with smaller
  brained Australopithecus species

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Homo erectus

• Java man and Beijing man
• First hominid to leave Africa and expand its
  range into Europe and Asia
• 1.8 mya- 250,000 ybp
• Larger brain, intelligence allowed early humans
  to inhabit inhospitable climates

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Homo sapiens Neanderthals CroMagnon
Homo erectus 1st to leave Africa
Homo habilis
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Two Theories About the Dominance of Homo sapiens
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Comparing Mitochondrial DNA between living humans
can be used to reconstruct our evolution
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Comparison of DNA sequences
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Sequence divergence among human
populations African population is the
oldest Australian, Caucasian, and New Guinean
diverged at about the same time
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Evolutionary Relationships of Human populations
based on Mt DNA Sequences
Australian
Caucasian
Asian
African
New Guinean
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DNA analysis supports the Out of Africa
hypothesis of human evolution