Charles Darwin

Charles Darwin

Middle School

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Learning Objectives

• Describe Charles Darwin's voyage on the HMS Beagle and his key observations.

• Explain Darwin's theory of evolution by natural selection.

• Outline the four steps of natural selection: overproduction, variation, competition, and selection.

• Define key terms such as adaptation, fitness, and evolution.

Key Vocabulary

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Natural Selection

The process where organisms with beneficial traits are more likely to survive and reproduce.

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Evolution

The process by which modern organisms have descended from ancient organisms over time.

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Adaptation

An inherited trait that increases an organism's chances of surviving in its environment.

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Fitness

A measure of an organism's ability to survive and reproduce in its environment.

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Theory

A well-supported, testable explanation for phenomena that occur in the natural world.

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Darwin's Voyage on the HMS Beagle

• In 1831, Charles Darwin began a five-year journey on the ship HMS Beagle.

• He observed an earthquake and found seashell fossils high in the mountains.

• Darwin unearthed fossils of giant extinct animals, like the ground sloth.

• His findings suggested that both Earth and its life forms change over time.

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Multiple Choice

Which of Darwin's observations provided direct evidence that organisms have changed over time?

• Seeing many new plants and animals in a tropical rainforest.

• Experiencing an earthquake that lifted the ocean floor.

• His voyage taking five years instead of three.

• Finding fossils of gigantic extinct mammals.

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Darwin's Discoveries on the Galápagos Islands

Saddle-Shaped Shells

• Tortoises on islands with taller plants had shells that were raised at the front.

• This unique saddle-like shape allowed them to stretch their necks to reach high branches for food.

• These tortoises were perfectly adapted to survive in their specific environment on the island.

Dome-Shaped Shells

• Tortoises on islands with low-lying grass and shrubs had rounded, dome-shaped shells.

• This shape was suited for environments where food was easily accessible on the ground.

• These differences caused Darwin to wonder how new species develop over time.

Multiple Choice

What was the significance of the different tortoise shell shapes Darwin observed on the Galápagos Islands?

• It suggested that species adapt to their specific environments and food sources.

• It showed that all animals on the islands were identical.

• It was simply an interesting detail with no scientific importance.

• It proved that all tortoises came from a single island.

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Darwin's Theory of Evolution

Evolution Occurs

• Darwin stated that all living things on Earth are constantly changing over very long periods.

• He explained that different species often share a common ancestor from the distant past.

• These species slowly changed over generations, leading to the diversity of life on our planet.

Natural Selection

• Natural selection is the process that explains how this evolution or change actually happens.

• Individuals with inherited traits that are best suited to their environment tend to survive longer.

• These survivors are then more likely to reproduce and pass on those helpful traits to their young.

Multiple Choice

What are the two central ideas in Darwin's theory of evolution?

• The Earth is 6,000 years old and species are unchangeable.

• Survival of the fittest means only the strongest survive.

• Organisms can evolve during their own lifetime.

• Evolution occurs, and it happens through natural selection.

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The Steps of Natural Selection

• Organisms produce more offspring than can survive, leading to a struggle.

• ​Natural differences (variations) exist; an adaptation is a trait improving survival.

• Individuals compete for resources; fitness is the ability to survive and reproduce.

• Selection acts on phenotype (physical traits), so the best-adapted individuals survive.

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Multiple Choice

According to the steps of natural selection, what is the direct result of overproduction?

• All offspring surviving to adulthood.

• The appearance of new adaptations.

• Competition for limited resources.

• A lack of variation within the species.

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Common Misconceptions About Evolution

Misconception	Correction
"Survival of the fittest" means only the strongest and fastest survive.	Fitness means being well-adapted to an environment to survive and reproduce.
Individual organisms can evolve during their lifetime.	Evolution happens to populations over many generations, not to one individual.
Humans evolved directly from monkeys.	Humans and modern apes share a common ancestor from the distant past.

Multiple Choice

Why were Darwin's observations of tortoises with different shell shapes on different Galápagos islands so important for developing his theory?

• It demonstrated how species might adapt to different local environments.

• It showed that all tortoises were identical.

• It was the first time anyone had seen a tortoise.

• It proved that tortoises could change their shells at will.

Multiple Choice

How do the concepts of 'overproduction' and 'competition' relate to each other in the process of natural selection?

• The two concepts are unrelated in natural selection.

• Overproduction creates a surplus of organisms, leading to competition for resources.

• Competition leads to overproduction of offspring.

• Overproduction reduces the need for competition.

Multiple Choice

A population of plants lives in a dry environment. Most have short roots, but a few have long roots. If a long drought occurs, what is the most likely outcome for the population over many generations due to natural selection?

• The entire population will become extinct immediately.

• The plants with long roots will be better able to survive and reproduce, passing on the trait for long roots.

• The drought will have no effect on the population's traits.

• The plants with short roots will learn to grow longer roots.

Multiple Choice

How did the discovery of fossils from extinct animals, like the giant ground sloth, challenge the prevailing scientific beliefs of Darwin's era?

• It confirmed the belief that species were created at the same time and never change.

• It proved that the Earth was only 6,000 years old.

• It showed that fossils were just unusually shaped rocks.

• It provided strong evidence that life on Earth was not static and had changed significantly over time.

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Summary

• Charles Darwin developed the theory of evolution by natural selection.

• He observed unique, adapted species on the Galápagos Islands.

• Evolution is how organisms change over time, driven by natural selection.

• The four steps of natural selection are Overproduction, Variation, Competition, and Selection.

• An adaptation is an inherited trait that helps an organism survive and reproduce.

• Darwin published his theory in his book 'On the Origin of Species'.

Poll

On a scale of 1-4, how confident are you about explaining Darwin's theory of natural selection?

• 1

• 2

• 3

• 4