History of EVOLUTIONARY THEORY &
DARWIN & NATURAL SELECTION
Ms. KimHonors Biology
• On November 24, 1859, Charles Darwin published On the Origin of Species by Means of Natural Selection.
• Darwin’s book drew a cohesive picture of life by connecting what had once seemed a bewildering array of unrelated facts.
• Darwin made two points in The Origin of Species:– Today’s organisms descended from ancestral
species.– Natural selection provided a mechanism for
evolutionary change in populations.
Introduction
What is the difference between Hypothesis and Theory?
Hypothesis: Tentative explanation of observations
Theory: General explanation of important natural phenomena, developed through extensive & reproducible observations &
experiments
What is a Scientific Theory?• A theory in science is not a “guess”• It represents the best model for making sense out
of all the evidence.– Germ theory, Electrical theory, Cell theory, etc.
• Evolution is a well-supported theory drawn from a variety of sources of data:– Observation of the fossil record– Genetic information– Distribution of plants and animals– Similarities across species of anatomy and
development
Darwin made two major points in his book called
Origins of Species:1. Many current species are descendants of ancestral species
2. Natural selection is a mechanism for this evolutionary process
Nature and Classification of Species• Greek philosopher Aristotle– organisms were perfectly formed and adapted to
the world (fixed and unchanging)
– Saw adaptations as evidence that a Creator had designed each species for a specific purpose
– founder of taxonomy (biology concerned with classifying organisms) & binomial nomenclature (scientifically naming organisms- Species genus)
Carolus Linnaeus (1707-1778)
“King Philip Came Over For Good Spaghetti”
Fossils, Cuvier, and Catastrophism
• The study of fossils helped to lay the groundwork for Darwin’s ideas• Fossils • remains or traces of organisms from
the past, usually found in sedimentary rock, which appears in the layers or strata
Western Historical Context
French anatomist who largely developed paleontology, the study of fossils
Georges Cuvier (1769-1832)
Western Historical ContextGeorges Cuvier (1769-1832)
Deeper strata contain older taxa
Preferred hypothesis for profound geologic change = catastrophism = Stated that species disappear due to a catastrophic event of the earth’s
crust (volcano, earthquake…)
Western Historical Context
Scottish geologist who offered an alternative to catastrophismJames Hutton (1726-1797)
Preferred hypothesis for profound geologic change = gradualism
Changes in Earth’s crust due to slow continuous processes (erosion, earthquakes, volcanoes…)
Charles Lyell (1797-1875)Proposed theory of
UniformitarianismGeological processes
at uniform rates building & wearing down Earth’s crust
Proposed that the Earth was millions of years instead of a few thousand years old
Western Historical ContextJean Baptiste Lamarck (1744-1829)
•Stated that Changes Are Adaptations To Environment acquired in an organism’s lifetime•Said acquired changes were passed to offspring
Lamarck’s Theory of Evolution (1809)
• Lamarck hypothesized species evolve through• use and disuse and • inheritance of acquired traits• Tendency toward perfection
• The mechanisms he proposed are unsupported by evidence
Lamarck’s Theory of Evolution• Idea called Law of
Use and Disuse• If a body part
were used, it got stronger• If body part NOT
used, it deteriorated
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inheritance of acquired traits
• Will his kids be born with big muscles because he has them?
WILL THE OFFSPRING BE NICELY PRUNED?
Tendency toward Perfection
• Organisms are continually changing and acquiring features that help them live more successfully in their environment.
• Example: Bird Ancestors Desired to Fly So they tried until wings developed.
Lamarck’s Mistakes
• Lamarck did NOT know how traits were inherited (traits are passed through genes)
• Genes are NOT changed by activities in life• Change through mutation occurs before an
organism is born.
Western Historical ContextThomas Malthus (1766-1834)
•English demographer
•Hypothesis: Plants and animals are capable of producing far more offspring than resources can support; the “struggle for existence” (e.g., famine, war) is an inescapable consequence
• Each Species Struggles For:– Food– Living Space– Mates
Charles Darwin (1809-1882)
• LOVED nature• Sails on HMS Beagle at 22 and
voyaged around world• Noted flora and fauna on islands
off of South America• Contributions of Lyell, Hutton and
Malthus lead him to his mechanism for evolution• species change through natural
selection• http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html
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What is Evolution?
• Evolution is the slow, gradual change in a population of organisms over time
What was the Voyage of the Beagle?
Charles Darwin Joined Crew of HMS Beagle, 1831 Naturalist 5 Year Voyage around world Collected specimens of South American
plants and animals Observed adaptations of plants and
animals that inhabited many diverse environments
Main focus of geographic distribution of species = Galápagos Islands near the equator west of South America
Darwin Left England in 1831
Darwin returned 5 years later in 1836
The Galapagos Islands• Small group of islands
1000 km west of South America• Very different climates• Animals on islands
unique–Tortoises– Iguanas–Finches
What are The Galapagos Islands? Island species varied
from mainland species & from island-to-island species
Each island had long or short neck tortoises
What are Characteristics of Galapagos Finches?
Finches on the islands resembled a mainland finch
More types of finches appeared on the islands than the mainland
Finches had different types of beaks
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Darwin’s Focus on Adaptation• Adaptation= a change in structure or
habits, often hereditary, to improve survival and reproduction in environment– Adaptation to environment and the origin of
new species are closely related processes• EXAMPLE– Finches on the islands resembled a
mainland finch– Finches had different types of beaks
adapted to their type of food gathering
LE 22-6
Cactus eater. The long, sharp beak of the cactus ground finch (Geospiza scandens) helps it tear and eat cactus flowers and pulp.
Seed eater. The large ground finch (Geospiza magnirostris) has a large beak adapted for cracking seeds that fall from plants to the ground.
Insect eater. The green warbler finch (Certhidea olivacea) used its narrow, pointed beak to grasp insects.
Darwin’s Overall Observations• Left unchecked, the # of
organisms of each species will increase• In nature, populations
tend to remain stable in size• Environmental resources
are limited
More of Darwin’s Observations• Individuals of a
population vary in characteristics with no 2 individuals being exactly alike.
• Much of this variation between individuals is inheritable.
Darwin’s Overall Conclusions#1. Variation exists in every
population which may have been inherited and the result of a mutation
#2. Production of more individuals than can be supported by the environment leads to a struggle for existence among individuals• Only a fraction of offspring
survive each generation• Survival of the Fittest
Darwin’s Conclusion
#3. Adaptation: Individuals who inherit characteristics (adaptations) that are most fit (suitable/favorable) for their environment are likely to leave more offspring than less fit individuals• Called FITNESS
• High survival = more offspring = more fit
#4. Descent with Modification. Over time these adaptations will increase in the population.
What is Common Descent with Modification?
Darwin proposed that organisms descended from common ancestors
Idea that organisms change with time, diverging from a common form
Caused evolution of new species Takes Place Over Long Periods of Time Species Today Look Different From
Their AncestorsEach Living Species Has○ Descended With Changes From
Other Species Over Time
Darwin’s Descent with Modification• descent with
modification• refers to idea that
all organisms are related through descent from common ancestor that lived in the remote past• the history of life is
like a tree
Having good “biological fitness” means you are the strongest and biggest.
TrueFalse
What are Adaptations?Inherited Characteristic That Increases an
Organisms Chance for Survival Adaptations Can Be:
Physical○Speed, Camouflage, Claws, Quills, etc.
Behavioral○Solitary, Herds, Packs, Activity, etc.
Darwin’s Conclusion• Natural Selection–gradual, nonrandom process by which traits
become more/less common in a population–Acts on PHENOTYPES (adaptations), which
influences GENOTYPES–only organisms best adapted to environment
tend to survive and transmit genetic traits to future generations while those less adapted tend to be eliminated
• Key mechanism to evolution
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Natural Selection
Cannot Be Seen Directly It Can Only Be Observed
As Changes In A Population Over Many Successive GenerationsRadiationFossil Record
http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html• Video #4: How Does Evolution Really Work?
• 1844• Darwin wrote an essay on natural selection
but did not publish it• 1858• Alfred Russell Wallace developed a
similar theory of natural selection to Darwin’s (organisms evolve from common ancestors)
• Darwin quickly finished The Origin of Species and published it the next year
Darwin’s 1st Idea: Evolution• What is evolution?– All accumulated changes across successive
generations in inherited characteristics of populations– A change over time in the genetic combination in a
population give rise to diversity• Darwins definition = Descent with
modificationDarwin’s 2nd Idea: Natural Selection
• If an environment changes over time, natural selection may result in adaptation to these new conditions new species can also evolve
What are the 4 conditions of Darwin’s Theory of Evolution by Natural
Selection?
• Population has variations. • More offspring are produced than
survive• Some variations are favorable. Those
that survive have favorable traits. • A population will change over time.
Use Inheritance of acquired
characteristics
Generation 1 Generation 2
Naturalselection
Genetic inheritance from
selected population
Lamarckism
Darwinism