Chapter 15: Darwin’s Theory of Evolution

Pages 368-386

Chapter 15-1: The Puzzle of Life’s

DiversityPages 369-372

Vocabulary 15-1

evolutiontheoryfossil

Evolution

Definition: change over time, the process by which modern organisms have descended from ancient organisms

The Theory of Evolution helps us understand

how:• fossils fit into life’s history• bacteria become resistant to

antibiotics & insects to pesticides

• determine the relationships among the different groups of organisms on Earth

Charles Darwin• Born Feb.12, 1809 in England• Sailed on the H.M.S. Beagle in 1831

for a 5 year voyage around the world

• Made many observations & collected evidence that caused him to hypothesize about how life changes over time

• His observations were influenced by reading the ideas of other scientists while at sea

Charles Darwin

Scientific beliefs before Darwin:

• Species were unchanging – the same organisms always existed.

• Earth was about 10,000 years old.

Darwin’s Observations

1. A large variety of organisms inhabit the Earth • Example: He collected 68 species of

beetles in 1 day in a rainforest in Brazil

2. Organisms were well suited for the different environments in which they were found

• Examples: On the Galapagos Islands, tortoises from different islands have different shaped shells & neck lengths and different finches (birds) have different shaped beaks

Fossils

• Definition: preserved remains of ancient organisms

• Fossil evidence raises many questions:• Why have so many species disappeared?• How do extinct organisms relate to

living organisms?

• Darwin based most of his beliefs on the fossils he found and wondered if animals on different islands once belonged to the same species

Review: Species

Definition: organisms belong to the same species if they can interbreed (produce fertile offspring) under natural conditions

Good News:

We are skippingChapter 15-2.

To summarize Chapter 15-2:

Many scientists contributed ideas that helped frame Darwin’s theory, ideas such as:

1) The Earth is actually millions of years old and is still changing…

2) Organisms acquired or lost certain traits during their lifetime that could be passed onto offspring, thus changing a species (later proved false)…

3) If a population grows unchecked, sooner or later, food and space will run out…

Chapter 15-3: Darwin Presents His Case

Pages 378-386

Vocabulary 15-3natural variationstruggle for existencefitnessadaptationsurvival of the fittestnatural selectioncommon descenthomologous structurevestigial organ

Darwin’s Book

•Darwin collected his ideas and published the book “On the Origin of Species” which proposed:– A mechanism of evolution he

called natural selection, based on three major principles

– That the process of evolution has been taking place for millions of years

Principle #1: Natural Variation

• Definition: differences among individuals of a species

• Darwin argued that natural variation is found in all species

• These “variations” can be passed on to the next generation

These natural variations occur through:

• Sexual reproduction• Independent assortment of

chromosomes• Segregation of alleles• Crossing-over during meiosis• Mutations in DNA

Principle #2: Struggle for Existence

Members of each species compete for living space, food, and other things needed for them to:

SURVIVE AND REPRODUCE.

Principle #3: Survival of the Fittest

1) The greater fitness an organism has, the more likely it is to survive in an environment (i.e. “win the struggle”).

Fitness: is the ability of an organism to survive and reproduce in an environment

2) Fitness is the result of adaptations.

Adaptations: any inherited characteristic that increases an organism’s chance of survival

• Example: can be physical (porcupine quills) or behavioral (hunting in a pack)

Darwin’s Theory of Evolution by Natural

Selection• Individuals with high levels

of fitness survive and reproduce the most offspring – survival of the fittest.

• Individuals not suited to their environment (low fitness) either die or produce small number of offspring.

Common Ancestry• Definition: all living organisms

are related to one another• Common descent: all species –

living and extinct – came from common ancestors

Evidence for Evolution

1. The Fossil Record

• Fossil: preserved remains of an ancient organism; formed by sediment settling over remains

• Fossil records are incomplete – many organisms have lived and died and were never preserved

• Fossils in the same layer of rock lived at the same time

• Shows how some organisms change slowly over time

• Show how complex animals and plants of today were preceded by simpler ones

The “fishapod”…375 million years old…may be the link between water and land.

“Ida”…47 million years old…possibly the missing link in primate evolution.

2. Geographic Distribution of Species

• Isolated land areas and island groups evolve their own distinct plants and animals fit to the environment

• The same kinds of fossils are found in areas which were once connected (ex. Pangaea, the “supercontinent”) but now separated as a result of continental drift

• Many different organisms have similar body structures – which may perform different functions but are constructed of the same basic bones and tissues

• Vestigial organ: organ that is so reduced in size it does not perform a function

3. Homologous Body Structures & Vestigial

Organs

4. Embryonic Development

• Embryos of closely related organisms have similar early stages of development

5. Molecular Analysis

• If two species have genes and proteins sequences that match closely, biologists conclude that the sequence was copied from a relatively recent common ancestor