Evolutionary Trees

Evolutionary Trees

By Stefan Mejia-Ott

Earth is inhabited by millions of different kinds of living things, called species.

A species is a group of organisms that share traits and can breed successfully with one another but not with other groups.

Humans, tulips, and cheetahs are all different species. How did Earth end up with so many species?

Multiple Choice

__________ is a group of organisms that share traits and can breed successfully with one another.

• Animal

• Plan

• Species

• Mutant

Charles Darwin searched for an explanation for this after the voyage of the Beagle.

Darwin argued that all organisms—all species—are descended from a single ancestor.

Scientists now know that this ancestor was a single-celled organism that lived about 3.7 to 4 billion years ago.

Multiple Choice

Darwin thought that all species descended from ______________.

• Many different ancestors

• Apes

• Animals

• A single ancestor

Multiple Choice

Scientists now know that this ancestor was a

• germ

• single-celled organism

• gorilla

• a multi-celled organism

Related species share a common ancestor.

A common ancestor is an ancestor from which two or more different species evolved, or descended.

Related species share traits that they inherited from their common ancestors.

For example, all mammals have hair and feed their young milk.

Mammals share these traits because the common ancestor of mammals had hair and fed its young milk.

The descendants of this ancestor—all mammals—inherited these traits.

Multiple Choice

______________ is an ancestor from which two or more different species evolved, or descended.

• Uncommon Ancestor

• Unique Ancestor

• Common Ancestor

• Grandparent

Multiple Choice

Related species share ____________ they inherited from their common ancestors.

• Beliefs

• Traits

• Religions

• Personalities

Multiple Choice

What traits did mammals inherit from their common ancestor?

• Hair and being able to feed their young.

• Fins and being able to breathe underwater.

• Feathers and being able to fly.

• Scales and being able to camouflage.

Birds and mammals also share certain traits. Both groups have a backbone, four limbs, and lungs.

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On the other hand, bony fishes have a backbone, but they do not have limbs or lungs. How are bony fishes, birds, and mammals related?

The evolutionary relationships among mammals, birds, and bony fishes can be shown using an evolutionary tree.

An evolutionary tree is a diagram with “branches” that shows how different groups of organisms are related.

This evolutionary tree shows that mammals and birds are more closely related, while bony fishes are more distantly related.

Circles along the branches show some traits of the organisms. For example, mammals and birds have lungs and four limbs, but only birds have wings.

Multiple Choice

Evolutionary trees show _______________. (Choose the best answer)

• The traits of different groups of organisms

• the relationships among groups of organisms

• The common ancestor of a certain group of animals

• The genes inherited by a certain group of organisms.

Multiple Choice

This evolutionary tree shows that ________ and _________ are more closely related.

• Mammals and reptiles

• Birds and Fish

• Mammals and fish

• Mammals and birds

Multiple Choice

This evolutionary tree also shows some of the ____________ of all these organisms.

• Species

• Genes

• Traits

• Common ancestor