AP Biology
Lecture #39
Introduction to Evolution
Descent with
Modification: A Darwinian
View of Life
Evolution
• Evolution: the change over time of the
genetic composition of populations
• Natural selection: populations of
organisms can change over the
generations if individuals having certain
heritable traits leave more offspring
than others (differential reproductive
success)
• Evolutionary adaptations: a prevalence
of inherited characteristics that
enhance organisms’ survival and
reproduction
November 24, 1859
Triassic
Permian
225
Carboniferous
350
Devonian
Silurian
Ordovician
Cambrian
Ediacaran
400
430
500
570
700
Precambrian,
Proterozoic,
&
Archarozoic 4500
Life’s Natural History is a record of Successions & Extinctions
Seed Plants
Land Plants
Birds
Mammals
Reptiles
Insects
Amphibians
Teleost Fish
Jawless Fish
Chordates
Arthropods
Molluscs
280
Flowering Plants
180
Dinosaurs
Jurassic
135
Multicellular Animals
Cretaceous
63
Green Algae
Tertiary
1.5
Photosynthetic Bacteria
Quaternary
Anaerobic Bacteria
mya
Evolutionary history
•
•
•
•
•
Linnaeus: taxonomy
Hutton: gradualism
Lamarck: evolution
Malthus: populations
Cuvier: paleontology
•
•
•
•
Lyell: uniformitarianism
Darwin: evolution
Mendel: inheritance
Wallace: evolution
Mid-Eighteenth-Century Contributions
Carolus Linnaeus and Taxonomy
a. Taxonomy is the science of classifying
organisms;.
b. Carolus Linnaeus (1707–1778) was a Swedish
taxonomist.
1) Linnaeus developed a binomial system of
nomenclature (two-part names for each species
[e.g.,
Homo sapiens]).
2) Like other taxonomists of his time, Linnaeus
believed in the ideas of
a) special creation—each species had
an “ideal” structure and function; and
b)fixity of species—each species had a place in
the scala naturae, a sequential ladder of life.
2. Georges Louis Leclerc
a. Georges Louis Leclerc, known by his title, Count Buffon
(1707-1788), was a French naturalist.
b. He wrote on the natural history of all known plants and
animals, provided evidence of descent with modification.
c. His writings speculated on influences of the environment,
migration, geographical isolation, and the struggle for
existence.
In the course of his examination of the animal
world, Buffon noted that despite similar
environments, different regions have distinct plants
and animals, a concept later known as Buffon's
Law, widely considered the first principle of
biogeography.
3. Erasmus Darwin
a. Erasmus Darwin (1731-1802) was Charles Darwin's grandfather.
b. He was a physician and a naturalist whose writings on both botany
and zoology contained many comments that suggested the possibility
of common descent.
c. He based his conclusions on
1) changes undergone by animals during development,
2) artificial selection by humans
3) the presence of vestigial organs
Erasmus Darwin offered no mechanism by which
evolutionary descent might occur.
Late Eighteenth-/Early-Nineteenth Century Contributions
1. Cuvier and Catastrophism
a. George Cuvier (1769-1832), a French vertebrate zoologist,
was the first to use comparative anatomy to develop a system
of classifying animals.
b. He founded the science of paleontology-the study of fossilsand suggested that a single fossil bone was all he needed to
deduce the entire anatomy of an animal.
c. To explain the fossil record, Cuvier proposed that a whole
series of catastrophes (extinctions) and repopulations from
other regions had occurred.
d. Catastrophism is the term applied to Cuvier's explanation
of fossil history: the belief that catastrophic extinctions
occurred, after which repopulation of surviving species
occurred, giving an appearance of change through time.
2. Lamarck's Acquired Characteristics
a. Lamarck (1744-1829) was the first to state that descent with
modification occurs and that organisms become adapted to their
environments.
b. Lamarck, an invertebrate zoologist, held ideas at odds with Cuvier's.
c. Lamarck mistakenly saw "a desire for perfection" as inherent in all living
things.
d. Inheritance of acquired characteristics was Lamarck's
belief that organisms become adapted to their
environment during their lifetime and pass these
adaptations to their offspring.
e. Experiments fail to uphold Lamarck's inheritance of
acquired characteristics
How could you test
Lamarck's theory?
What We Know So Far
1. Taxonomy and classification emphasize similarities
among species (common descent)
2. Fossils show extinct species (paleontology)
3. Isolated species are distinct (biogeography)
4. Organisms have adaptations to help them survive
*At this point, no mechanism has been proposed to
explain how these adaptations come to be
* Special creation is still strongly held, but offers no
explanation for the appearance of new species (like on
an island)
........................Enter Charles Darwin............................
Charles Darwin
• 1809-1882
• British naturalist
• Proposed the idea of
evolution by natural
selection
• Collected clear
evidence to support
his ideas
Voyage of the HMS Beagle
• Invited to travel around the world
– 1831-1836 (22 years old!)
– makes many observations of nature
• main mission of the Beagle was to chart
South American coastline
Stopped in Galapagos Islands
500 miles off coast of Ecuador
Darwin found… birds
Collected many different
birds on the Galapagos
Islands.
Finch?
Sparrow?
Thought he found
very different kinds…
Woodpecker?
Warbler?
But Darwin found… a lot of finches
Darwin was amazed to
find out:
All 14 species of birds
were finches…
But there is only one
species of finch on the
mainland!
Large Ground
Finch
Small Ground Finch
Sparrow?
How did
one species
of finches become
so many different
species now?
Warbler Finch
Woodpecker?
Veg. Tree Finch
Warbler?
Darwin’s finches
• Differences in beaks
– associated with eating different foods
– survival & reproduction of beneficial adaptations
to foods available on islands
Warbler finch
Cactus finch
Woodpecker finch
Sharp-beaked finch
Small insectivorous
tree finch
Large
insectivorous
tree finch
Small ground
finch
Cactus
eater
Insect eaters
Medium
ground finch
Seed eaters
Vegetarian
tree finch
Bud eater
Large
ground finch
Darwin’s finches
• Darwin’s conclusions
– small populations of original South American finches
landed on islands
• variation in beaks enabled individuals to gather food
successfully in the different environments
– over many generations, the populations of finches
changed anatomically & behaviorally
• accumulation of advantageous traits in population
• emergence of different species
Seeing this gradation &
diversity of structure in
one small, intimately related group of birds,
one might really fancy that
from an original paucity of birds
in this archipelago,
one species has been taken &
modified for different ends.
Darwin’s finches
• Differences in beaks
allowed some finches
to…
– successfully compete
– successfully feed
– successfully
reproduce
• pass successful traits
onto their offspring
More observations…
Correlation of species
to food source
Whoa,
Turtles, too!
Essence of Darwin’s ideas
• Natural selection
– variation exists in populations
– over-production of offspring
• more offspring than the environment can support
– competition
• for food, mates, nesting sites, escape predators
– differential survival
• successful traits = adaptations
– differential reproduction
• adaptations become more
common in population