Chapter 16: Darwin’s Theory
of Evolution
16-1 Darwin’s Voyage of Discovery
•1831, Darwin set sail on HMS Beagle
•Ship’s naturalist -observer/collector of plants, animals, &
fossils
•Left from England, sailed around South America, across
Pacific, around Africa, and back to England
•Most famous for observations made at Galapagos Islands
•Biological evolution – change of populations of organisms
over time
16-1 Darwin’s Voyage of Discovery
• Darwin noted 3 patterns of biodiversity:
•Species vary globally – different, yet ecologically similar
animal species inhabited separate, but ecologically similar,
habitats around the globe (rheas, ostriches and emus)
•Species vary locally – different, yet related animal species
occupied different habitats within a local area (tortoise
shell shape - Galapagos)
•Species vary over time – fossils of extinct animals were
similar to living species
16-1 Darwin’s Voyage of Discovery
• Darwin noted 3 patterns of biodiversity:
•Species vary globally – different, yet ecologically similar
animal species inhabited separate, but ecologically similar,
habitats around the globe (rheas, ostriches and emus)
16-1 Darwin’s Voyage of Discovery
• Darwin noted 3 patterns of biodiversity:
•Species vary locally – different, yet related animal species
occupied different habitats within a local area (tortoise
shell shape - Galapagos)
16-1 Darwin’s Voyage of Discovery
• Darwin noted 3 patterns of biodiversity:
•Species vary over time – fossils of extinct animals were
similar to living species
16-2 Ideas That Shaped Darwin’s Thinking
Darwin was influenced by:
• James Hutton - proposed that layers of rock
form very slowly
– Some rocks move up, while others are buried to
create mountains and valleys.
– Natural forces such as rain and temperature
shaped the landscape
– These processes happen very slowly over
millions of years
16-2 Ideas That Shaped Darwin’s Thinking
•Charles Lyell – said earth was several million years
old
•Earth changed over time due to geologic forces
(volcanoes, earthquakes, wind, erosion, etc.)
•Darwin reasoned that if Earth changed, those who
lived on it would have to adapt/change to survive.
16-2 Ideas That Shaped Darwin’s Thinking
•Jean-Baptiste de Lamarck
suggested that organisms
acquired traits during their
lifetime to adapt to their
environment and passed those
acquired traits onto their
offspring.
•WRONG – only traits found
on genes can be passed onto
offspring!!
16-2 Ideas That Shaped Darwin’s Thinking
•Thomas Malthus – an economist
that said the human population
was limited by the supply of food
and living space.
•Darwin reasoned that the same
limits could apply to organisms in
nature.
16-2 Ideas That Shaped Darwin’s Thinking
• Natural Variation – differences among individuals
of a species.
• Farmers depend on natural variation for selective
breeding
– Only the largest hogs would be bred.
• Artificial Selection – humans selected the
variations that they find useful.
16-3 Darwin Presents His Case
•Darwin published his findings in 1859 in a book
entitled The Origin of Species by Means of Natural
Selection.
•He was motivated to publish his book in 1859 because
Alfred Wallace had independently come up with the
same conclusions
16-3 Darwin Presents His Case
Adaptations vs. Variations
•Variations – differences that exist within a population
that may have no effect on fitness
•Ex: length of your thumb
•Adaptations – a variation that all members of a
population have inherited because that trait improves
fitness
•Ex: an opposable thumbs
16-3 Darwin Presents His Case
•Sources of variation:
•Mutations – individual genes change
•Ex: ATC  AGC
•Events during meiosis – during meiosis,
chromosomes get mixed up (crossing over) in
making eggs & sperm
•Random fusion of gametes – which sperm
fertilizes which egg – determined by chance
16-3 Darwin Presents His Case
•Three types of adaptations:
•Structural – physical features of an
organism
•Ex: long tongue to get food, sharp teeth
Camouflage
•Behavioral – actions an organism takes
•Ex: migration, tracking prey, storing
nuts, growing towards light
•Physiological – functioning/biochemical
processes
•Ex: venom, ink of octopus, protein in
web, respiration rate, digestive enzyme,
blood clotting
16-3 Darwin Presents His Case
• Populations become modified through natural
selection
• Natural selection - the process by which environment
acts on a population, determining which organisms
are most “fit.” Those organisms who are most “fit”
survive and reproduce more often than those who are
not.
• Fitness – reproductive success (“survival of the
fittest”)
16-3 Darwin Presents His Case
•Darwin noticed similarities between species seen on
mainland and island chains
•Thought similarities could be explained by descent
with modification – species came to new
environment, then changed over time as the species
adapted to its new environment.
16.4 Evidence of Evolution
• Fossils
• Anatomy
• Analogous structures
• Homologous structures
• Vestigial structures
• Embryology
• Biochemistry
• Direct observation
16.4 Evidence of Evolution
Fossil Evidence
•Fossils - the remains of past life
•Ex: shells, bones, teeth,
imprints
•Tell us age, habitat, diet, &
lifestyle of organisms.
•Record is incomplete – many
organisms leave no fossils
behind
16.4 Evidence of Evolution
Anatomical Evidence – Homologous Structures
• All vertebrate forelimbs contain the same sets of bones –
suggests they evolved from a common ancestor.
• Homologous structures - structures that are similar
because they develop from same tissues early in
development; may or may not have same jobs
• Ex: frog, lizard, bird, whale, cat, bat, and human
forelimbs
Bones of vertebrate
forelimbs
16.4 Evidence of Evolution
Anatomical Evidence – Analogous Structures
• Analogous structures - used for the same purpose but are
not due to a common ancestor
• Ex: bird wing & insect wing
16.4 Evidence of Evolution
• Vestigial structures – have no function in the
living organism but may have been used by its
ancestors.
• Ex: human appendix, python leg bones
Cormorant – flightless bird
16.4 Evidence of Evolution
•Embryology – the more similar the embryos are
at certain stages of development, the more
closely related they are thought to be.
16.4 Evidence of Evolution
Biochemical Evidence
• Universal genetic code – organisms use the same
triplet code and the same 20 amino acids in proteins
• All organisms have certain organic molecules in
common.
1.Hemoglobin - carries oxygen in blood
2. Cytochrome c - protein for cell respiration found
in almost all living cells
3. Hox genes – control development
Significance of biochemical
differences
16.4 Evidence of Evolution
•Direct observation – We’ve seen
evolution occur in cases like:
•The Grant’s studies of finches
on Daphne Major in the
Galapagos
•Bacteria becoming resistant to
antibiotics
•Insects that become resistant
to pesticides