Ch. 15 Darwin’s Theory of Evolution

• You can acquire new pants, but you can’t change your GENES!

Ch. 15 Outline

• 15-1: The Puzzle of Life’s Diversity– The Voyage of the Beagle

– Darwin’s Observations

– The Journey Home

15–1 The Puzzle of Life's Diversity

• What scientific explanation can account for the diversity of life?

• The answer is a collection of scientific facts, observations, and hypotheses known as the theory of evolution

• Evolution is defined as change over time.

• Evolution describes the process by which modern organisms have descended from ancient organisms.

• A scientific theory is a well-supported testable explanation of phenomena that have occurred in the natural world.

•What process is described by the Theory of Evolution?

• How modern organisms have descended from ancient organisms.

15-1 Voyage of the Beagle• Charles Darwin

contributed more to our understanding of evolution than any other scientist

• Charles Darwin was born in England in 1809

– In 1831 Darwin joined the crew of the H.M.S. Beagle as the ship’s naturalist

Voyage of the Beagle– The voyage of the Beagle lasted five

years

15-1 Voyage of the Beagle

• Darwin made numerous observations and collected many plant, animal and fossil specimens

• This led Darwin to propose a hypothesis about the way life changes over time.

– This hypothesis is now called the theory of evolution.

15-1 Darwin’s Observations

• Patterns of diversity– Many plants and

animals seemed well suited to their environment

15-1 Darwin’s Observations

• Patterns of diversity– Organisms

survived and reproduced in many different ways

– Not all organisms lived everywhere

• What three patterns of diversity did Darwin observe in organisms?

• The organisms were well suited to their environment, survived and reproduced in different ways, lived in a variety of places

15-1 Darwin’s Observations• Darwin collected

fossils– Fossil: Are

preserved remains of ancient organisms

• Some fossils Darwin collected resembled living organisms

15-1 Darwin’s Observations• Some fossils did not resemble any living

organisms

• As Darwin studied fossils, new questions arose.

• Why had so many of these species disappeared?

• How were they related to living species?

15-1 Darwin’s Observations• Darwin’s thoughts were greatly

influenced by his collection and observation of species on his visit to the Galapagos Islands.

15-1 Darwin’s Observations• The Galapagos Islands

– Are off the west coast of South America– Each Island has a different climate and

different organisms

– Darwin noticed that the birds had different shaped beaks on each island

15-1 Darwin’s Observations– Darwin noticed that the tortoises

had different shaped shells on each island

15-1 The Journey Home

• After returning to England, Darwin wondered if animals living on different islands had once been members of the same species.

15-1 The Journey Home

• According to this hypothesis, these separate species would have evolved from an original South American ancestor species after becoming isolated from one another.

• This hypothesis challenged the accepted views on the age of the earth and the origin of different species.

• Darwin did not publish his thoughts until twenty-three years after his voyage on the Beagle.

• What did Darwin hypothesize about the diversity of the species on the Galapagos Islands?

– The different species evolved from a common ancestor after they became isolated from each other.

Ch. 15 Outline

• 15-2: Ideas that Shaped Darwin’s Thinking– An Ancient, Changing Earth– Lamarck’s Evolution Hypotheses– Population Growth

15–2 Ideas That Shaped Darwin's Thinking

• About the same time Darwin was questioning the origin of life, other people were traveling around the world and making important discoveries.

• They also began to challenge established views about the natural world.

15–2 Ideas That Shaped Darwin's Thinking

• Some people, however, found Darwin's ideas too shocking to accept.

• Most Europeans in Darwin's day believed that the Earth and all its forms of life had been created only a few thousand years ago.

An Ancient, Changing Earth• James Hutton and Charles Lyell

were two geologists whose ideas influenced Darwin

• Hutton proposed that layers of rock form very slowly and others are pushed up from the sea floor to form mountains. (This takes a long time)

Lyell’s Principles of Geology

• Lyell believed that the same processes that changed the Earth in the past still operate in the present.

• Lyell’s and Hutton’s work influenced Darwin in two ways:

• 1) If the Earth can change over time (earthquakes, volcanoes) maybe life can change over time!

• 2) Life can change over time only if the earth is very old.

• Why did Darwin’s, Hutton’s and Lyell’s view of the age of the earth was not accepted by some scientists?

15–2 Ideas That Shaped Darwin's Thinking

• Jean-Baptiste Lamarck and Thomas Malthus were two other scientists who shaped Darwin’s thinking

• Lamarck proposed that new species changed over time by gaining or loosing certain traits in their lifetimes.

15–2 Ideas That Shaped Darwin's Thinking

• Lamarck had two ideas:1. Organisms can alter their bodies by “use

and disuse”

• Use: Use a structure and it will change• Disuse: Structures not used will disappear

2. Acquired characteristics can be inherited.• If you increase your muscle mass your

children will inherit your big muscles

Use and Disuse

Lamarck’s Evolution Hypotheses

• Although Lamarck’s ideas were incorrect, he was one of the first ones to realize that organisms are adapted to their environments and propose a theory of evolution.

• What are some acquired traits that are found in people today?

15–2 Ideas That Shaped Darwin's Thinking

• Another influence of Darwin was Thomas Malthus.

• Malthus published a book in which he stated that babies were being born faster than people were dying. If the trend continued:– food and living space will run out.

Population Growth

• Darwin thought this theory applied more to plants and other animals because humans usually only have one offspring at a time.

• How did Lamarck’s and Malthus’ theories influence Darwin?

Ch. 15 Outline

• 15-3: Darwin Presents His Case– Publication of On the Origin of Species– Inherited Variation and Artificial Selection– Evolution by Natural Selection– Evidence of Evolution– Summary of Darwin’s Theory

15-3 Darwin Presents His Case

• When Darwin returned to England in 1836, he continued to study the specimens he collected from the Galapagos Islands.

• Darwin discovered that the birds, tortoises, and plants that he collected looked like similar species on the South American mainland.

• However, the island species were different from each other and the mainland species.

Darwin Presents his Case

• Over 20 years later, Darwin published all his findings in a book called, On the Origin of Species.

• He didn’t publish it earlier because it went against the common beliefs about organisms.

Darwin Presents his Case

• Not only did Darwin propose the theory of evolution, he also proposed a mechanism of how evolution happens:

• The mechanism for evolution is called natural selection

Inherited Variation and Artificial Selection

• One of Darwin’s most important insights is that there is a lot of diversity within all species

• In inherited variation, organisms pass on their traits to their offspring. This randomly occurs in nature.

Inherited Variation and Artificial Selection

• In artificial selection, humans select for variations in nature that are useful.– The breeding of domestic animals and

plant crops are examples.

Evolution by Natural Selection

• Next, Darwin compared natural selection and artificial selection, and proposed his mechanism of how evolution occurs.

• Darwin realized that organisms competed for resources. This is called the struggle for existence.

Evolution by Natural Selection

• Darwin noted that organisms better suited to their environment (ex. Run faster, hide from predators) survived to reproduce and pass on their genes.

• This is called survival of the fittest.

Evolution by Natural Selection

• Fitness: The ability of an animal to survive and reproduce

• Adaptation: an inherited characteristic that increases an organism’s chance of survival

Evolution by Natural Selection

• Successful adaptations, Darwin enables organisms to survive and reproduce.– Types of adaptations

• Structures• Physiological processes• Behavior

Evolution of Natural Selection

• Survival of the fittest: individuals that are better suited for their environment survive and reproduce most successfully. This is called Natural Selection

• Over time, natural selection results in changes in the inherited characteristics of a population. These changes increases a species’ fitness in its environment.

Evolution of Natural Selection

• Darwin proposed that over long periods of time, natural selection produces organisms that have different structures. Species today look different than their ancestors

• Descent with Modification: Each living species has descended, with changes from other species over time.

Evolution of Natural Selection

• Descent with modification implies that all living species are related to each other

• All species, living and extinct were derived from a common ancestor

15-3 Evidence of Evolution

• Fossil Record

• Geographic Distribution of Living Species

• Homologous Body Structures

• Embryology

Fossil Cephalopods          Darwin argued that the fossil record provided

evidence that living things have been evolving for millions of years.

Evidence of Evolution

• Geographic Distribution of Living Species– Similar organisms found in different places on

Earth– Ex: Darwin’s Finches– Organisms under the same environmental

“pressures” in different locations had similar adaptations

Homologous Body Structures

• Structures that have different mature forms but develop from the same embryonic tissues– Ex. Wings and arms– Help Scientist determine common ancestors– Not all homologous structures serve important

functions

Homologous Structures

Turtle Alligator Bird Mammal

Ancient lobe-finned fish

Homologous Body Structures

• Vestigial Organs: Organs reduced in size (Traces of homologous organs in other species)– Have little or no function

Embryology

• Organisms that have similar developmental stages as embryos are more closely related to each other.

Summary of Darwin’s Theory

1. Individual organisms differ, and some of this variation is inheritable

2. Organisms produced more offspring that can survive and there is competition for limited resources

3. Individuals best suited to environment survive and reproduce. Others die or leave fewer offspring. This process of natural selection causes species to change over time.

4. Species alive today are descended with modifications.