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