7.1.5 Theory of Evolution

Theory of Evolution

7.1.5

Objectives

Learners can:

• define evolution and identify its key components

• explain how natural selection leads to adaptation

• describe how fossils provide evidence that supports the theory of evolution

• discuss the role of evolution in the diversity of life on Earth

• fossil

• natural selection

• speciation

• theory

Prerequisite Vocab

• theory of evolution

New Vocab

Vocabulary

states that species have their origin in common ancestors and that differences result from continuous change within a species

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Theory of Evolution

Categorize

Options (3)

organisms best suited to their environment pass on their genes to the next generation

a scientific claim supported by a great deal of evidence

the formation of new species

Match the vocabulary word to its definition.

natural selection

speciation

theory

Theory of Evolution

The theory of evolution states that species have their origin in common ancestors and that differences result from continuous change within a species. In his book On the Origin of Species, Darwin presented his theory by explaining how natural selection can lead to the formation of new species. He supported his claims using evidence that he studied on his travels, including fossil evidence and observations of diverse species around the world.

Three Key Components of Evolution

• all living things exhibit some level of variation;

• traits are heritable, meaning that offspring tend to inherit the

  variations of their parents;

• organisms with traits that help them survive and reproduce are more likely to pass on their genes to the next generation; and

Multiple Choice

Read the scenario below. Then, answer the question that follows.

Imagine a population of rabbits that lives in a forest. Some rabbits are born with brown fur, while others are born with white fur. The brown rabbits are better camouflaged in the forest, where the rabbits' predators are found. Over time, the proportion of the population of rabbits with brown fur will become greater.

Why will the population of rabbits become more and more brown over time?

• because brown fur is more attractive to potential mates

• because brown fur helps them find food more easily

• because brown fur helps them stay cool in hot weather

• because brown fur provides better camouflage from predators

Evidence for Evolution

Three key pieces of evidence fossils provide are:

• fossils show that different types of organisms have lived on Earth at different times;

• fossils show that organisms of similar types have changed over time; and

• fossils show that transitional forms existed.

Lived about 375 million years ago. The species' ability to move on land suggests a transition between aquatic and land-dwelling animals.

Tiktaalik

​Fossils from a group of organisms known as Cynodonts represent a transition to the earliest mammals. Paleontologists date many of these fossils to the Mesozoic era.

Cynodonts

​This reconstructed Australophithecus represents a transitional fossil between non-humanoid apes and the early ancestors of the human species. The fossils illustrate that primates have changed over time.

Australopithecus

Multiple Choice

Which of the following statements best describes the role of natural selection in the process of evolution?

• Natural selection is a non-adaptive process that hinders species survival.

• Natural selection intentionally selects traits to create new species.

• 
  Natural selection is a random process that leads to genetic diversity.

• 
  Natural selection favors traits that enhance survival in a given environment.

Natural selection can only work with the genetic variation already present in a population. Natural selection cannot lead to adaptation if there is no genetic variation for a particular trait.

Evolution's Impact on Biodiversity

Evolution has led to the diversity of life on Earth through speciation. New species result from the process of speciation. Speciation is a slow process, but it has led to Earth's incredible diversity of life. There are millions of different species of plants and animals on Earth, and each species is unique. This diversity is because organisms have evolved to adapt to different environments.

Different species of bears have evolved in many parts of the world. For example, polar bears live in the Arctic, and black bears live in North America. Scientists propose that all bear species evolved from a single North American species that lived about 10 million years ago.

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Bears

Many varieties of bacteria have evolved to live in different environments. For example, some bacteria live in hot springs, some bacteria live in the human gut, and other bacteria live in the soil. The different species of bacteria have evolved to adapt to various conditions.

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Bacteria