Download Chapter 17: Introduction to Darwinian Evolution

Chapter 17: Introduction to
Darwinian Evolution
Evolution
• Accumulation of inherited changes within
populations over time
• NOT changes in an individual in its lifetime
• Changes in characteristics of populations over
many generations
2 perspectives:
• 1) MICROEVOLUTION: short-term adaptations
of population to changes in the environment
• 2) MACROEVOLTUION: long-term formation of
different species from common ancestors
Contributing Scientists
• Jean Baptiste de Lamarck
– 1st – organisms undergo change because of
natural phenomena
– Organisms endowed with vital force to change
toward complexity over time
– Organisms could pass traits acquired during their
lifetimes to their offspring
• Giraffes – stretch necks
• Discredited when basis for heredity discovered
• Thomas Malthus
– Population growth not always desirable
– Outstrip food supply
– Famine, disease, war – stop growth
• “struggle for existence”
–  strong and constant check on human
population growth
• Charles Lyell
– Slow geological processes  Old Earth
• Charles Darwin
– HMS Beagle – South America – 5 years
– Naturalist – plants, animals, fossils, geology
– Galapagos Islands – compared species to
mainland and other Galapagos Islands
– Artificial selection: breeders develop varieties in a
few generations
• Dogs, plants
• Similar process in nature – model for natural selection
Fig. 22-9
Terminal
bud
Lateral
buds
Cabbage
Flower
clusters
Brussels sprouts
Leaves
Kale
Cauliflower
Stem
Wild mustard
Flowers
and stems
Broccoli
Kohlrabi
Fig. 22-5
GREAT
BRITAIN
EUROPE
NORTH
AMERICA
ATLANTIC
OCEAN
The
Galápagos
Islands
AFRICA
Pinta
Marchena
Santiago
Fernandina
Isabela
Genovesa
Daphne
Islands
Pinzón
Santa
Cruz
Florenza
Santa
Fe
AUSTRALIA
PACIFIC
OCEAN
San
Cristobal
Española
Equator
SOUTH
AMERICA
Cape of
Good Hope
Tasmania
Cape Horn
Tierra del Fuego
New
Zealand
– Favorable variations would be preserved,
unfavorable eliminated
–  adaptation : evolutionary modification that
improves the chances of survival and reproductive
success in a give environment
– Accumulation of modifications  maybe new
species
– Time required for new species to originate
• Old Earth
Fig. 22-6
(a) Cactus-eater
(c) Seed-eater
(b) Insect-eater
Fig. 22-2
Linnaeus (classification)
Hutton (gradual geologic change)
Lamarck (species can change)
Malthus (population limits)
Cuvier (fossils, extinction)
Lyell (modern geology)
Darwin (evolution, natural selection)
Wallace (evolution, natural selection)
American Revolution
French Revolution
U.S. Civil War
1800
1900
1750
1850
1795 Hutton proposes his theory of gradualism.
1798 Malthus publishes “Essay on the Principle of Population.”
1809 Lamarck publishes his hypothesis of evolution.
1830 Lyell publishes Principles of Geology.
1831–1836 Darwin travels around the world on HMS Beagle.
1837 Darwin begins his notebooks.
1844 Darwin writes essay on descent with modification.
1858 Wallace sends his hypothesis to Darwin.
1859 The Origin of Species is published.
Natural Selection (Darwin)
• Better adapted organisms are more likely to
survive and become parents
• Population changes over time; frequency of
favorable traits increase with each generation
4 observation for Natural Selection
• 1) Variation – each individual is unique
– Some advantageous traits - inherited
• 2) Overproduction – each species can produce
more offspring than can survive
• 3) Limits on Population Growth – (struggle for
existence) more individuals than resources 
competition
• 4) Differential reproductive success – (survival
of the fittest) better adapted individuals will
survive and reproduce
Fig. 22-10
Evidence for Evolution
•
•
•
•
•
Fossil Record
Comparative Anatomy
Biogeography
Developmental biology
Molecular evidence
Fossil Record
• Fossils – remains/traces of previously existing
organisms
– Sedimentary rock, bogs, tar, amber, ice
– Conditions slow or prevent decay
– Covered quickly – water, sand
– Hard body parts
– Record biased – location, body
Dating Fossils
• 1) Relative Age – position in rock
– Index fossils –
• characterize a specific layer over large geographical
areas
• Existed short time, preserved in large numbers
– With this info  arrange rock layers and fossils in
chronological order and identify comparable
layers in widely separated locations
Fig. 22-3
Layers of deposited
sediment
Younger stratum
with more recent
fossils
Older stratum
with older fossils
• 2) Absolute Age –
– Radioisotopes – emit radiation – nucleus changes
into nucleus of different element with decay
– Half-life – time required for ½ of the atoms to
change to a different atom
– Potassisum-40 (1.3 billion years)
– Uranium-235 (704 million years)
– Carbon-14 (5730 years)
Comparative Anatomy
• Similar structures  related organisms (common
ancestor)
• Homologous structures – features derived from
same structure in a common ancestor
– Ex: limb bones of mammals, modified leaves
– Similar structure, different function
• Homoplastic features (Analogous features) –
structurally similar features that are not
homologous but have similar functions in distantly
related organisms
– Ex: wings of insects/birds, spines and thorns
– Same function, evolved separately (different structure)
Fig. 22-17
Humerus
Radius
Ulna
Carpals
Metacarpals
Phalanges
Human
Cat
Whale
Bat
Fig. 22-20
Sugar
glider
NORTH
AMERICA
AUSTRALIA
Flying
squirrel
– Show organisms with separate ancestries may adapt in
similar ways to similar environmental demands 
Convergent evolution
• Ex: aardvarks, anteaters, pangolins
• Vestigial structures – organs or parts of organs that are
seemingly nonfunctional and degenerate, undersized or
lacking some essential part
– Remnants of parts that were functional in ancestors
– Ex:
•
•
•
•
•
Human - appendix, coccyx, 3rd molars, ear muscles
Whales/pythons – hind limb bones
Pigs – vestigial toes
Kiwi – wingless bird – vestigial wing bones
Burrowing/cave-dwelling – vestigial eyes
Vestige usually not harmful so selective pressure to completely
eliminate is weak
Biogeography
• Study of past and present geographical
distribution of organisms
• Not all animals/plants found in all
environments where they could survive
• Spread from origin
• Continental drift / Pangaea
Developmental biology
• Genetic similarities reflect shared evolutionary
history
• Vertebrates – embryological development
similar  common ancestor
– (segmentation, gill pouches, aortic arches)
Fig. 22-18
Pharyngeal
pouches
Post-anal
tail
Chick embryo (LM)
Human embryo
Molecular evidence
• Confirms structural and fossil evidence
• Universal genetic code
• Similar amino acid sequences, proteins,
nucleotides
• More similarities  common ancestor
• Phylogenetic trees - diagrams showing lines of
descent
– Derived from differences in DNA sequences
– Whales and hippos closely related
Evolution is happening NOW!
• Can be observed in our lifetime
• Ex:
– Resistant Bacteria
– Finch beaks
– Guppy study