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Principles of Evolution
Chapter 24
Classification of Humans
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Kingdom
Phylum
Class
Order
Family
Genus
Species
Animalia
Chordata
Mammalia
Primates
Hominidae
Homo
sapiens
Challenges to Early Beliefs
• Biogeography - discovery of species in isolated
locales
• Comparative morphology - similarities between
animals, parts with no functions
• Fossils - deep layers with simple fossils,
overlying layers with increasing complexity
Charles Darwin
• Proposed the theory of evolution by way
of natural selection
• Influenced by
– Observations made while naturalist on
H.M.S. Beagle
– Conversations with other naturalists
– Writings of Thomas Malthus
Variation in Populations
• Individuals do not evolve; populations
do
• Members of a population have similar
traits
• Details of traits vary among individuals
• Some variation results from genetic
differences (different alleles)
Mutation
• A heritable change in DNA
• Most are harmful
• Some are neutral
• A few are beneficial
Natural Selection
• Individuals vary
• Some variations are heritable
• Some versions of traits increase fitness
• Natural selection is the difference in
survival and reproduction in individuals
who have different versions of a trait
Evolving Populations
• A population is evolving when some
forms of a trait are becoming more or
less common relative to the other forms
• Over time, shifts in the makeup of gene
pools have been responsible for the
amazing diversity of life forms on Earth
Other Changes to Gene Pool
• Genetic drift
– Founder effect
– Virtually no Native Americans with
type B blood
• Gene flow
– Physical movement of alleles
– Helps keep neighboring populations
genetically similar
Species
• A genetic unit consisting of one or more
populations of organisms
• Members can interbreed and produce
fertile offspring under natural conditions
• Reproductively isolated from other species
Speciation
time A
time B
time C
time
time D
Fossils
• Usually hard parts
• Form in sedimentary rock
• Stratification
• Fossil record is biased
Biogeography
Distribution of plants and animals
Plate tectonics
Comparative Morphology
• Homology
• Analogy
– Similarity in body
parts in different
organisms
– Similarity in body
parts in different
organisms
– Attributable to
descent from a
common ancestor
– Attributable
to similar
environmental
pressures
Homologous Structures
Vertebrate forelimbs
Comparative Embryology
• Early vertebrate embryos strongly resemble one
another
• Same plan of development
Fish
Reptile
Bird
Mammal
Proportional Skull Changes
Chimpanzee
Human
Evidence from
Comparative Biochemistry
• Molecular clocks
– Neutral mutations
• Protein comparisons
– Cytochrome C
• Nucleic-acid comparisons
– Base-pairing of DNA or RNA from one species
to another
Extinctions - End of the Line
• Background extinction
– Local changing conditions
• Mass extinction
– Catastrophic global event
– 65 million years ago
– Probably asteroid impact
Adaptive Radiation
• New species of a lineage moves into a
wide range of habitats
• Has occurred in the human lineage
• Homo habilis remained in Africa
• H. erectus went to Europe, Asia
• H. sapiens evolved by 100,000 years
ago
Trends in Human Evolution
• Upright walking
• Refined hand movements
• Enhanced daytime vision
• Changes in dentition
• Changes in brain and behavior
Comparison of
Skeletal Organization
Trend toward Longer Life Spans
and Dependency
From Primates to Hominids
• 60 million years ago
– Tropical forests
– Small rodents, tree shrews
• 54 - 38 million years ago
– Primates in trees
• 36 million years ago
– Tree-dwelling anthropoids
• 10 - 5 million years ago
– First hominoids
Early Earth
• Primitive
atmosphere
– H2
– N2
– CO
– CO2
– Probably no O2
Complex Compounds Form
Organic compounds may have:
• Formed when lightning interacted with
gases in early atmosphere
• Assembled on clays in tidal flats
• Formed near hydrothermal vents
Emergence of First Living Cells
• Self-Replicating Systems
– RNA
– DNA
• Plasma Membranes
– Proto-cells