Evolution — Part 2: Tracing relationships, fossils and human evolution: visual lesson, CBSE Class 10 Science

Lesson

Tracing evolution

Part 2 — how body structures, fossils and DNA reveal family relationships among living things, and where humans fit in.

In this lesson you will

Explain how shared characteristics show evolutionary relationships
Distinguish homologous and analogous organs with examples
Explain what fossils are and how their age is found
Explain how complex organs evolve in stages, and outline the common origin of humans

Concept

Classification follows evolution

The more characteristics two kinds of organism share, the more recently they shared a common ancestor, and the more closely related they are. So classifying organisms by shared features also traces their evolution.

Table comparing humans with a mouse, a frog and a fish by shared features, showing that more shared features mean a closer relationship
Organisms compared	Shared features	Relationship
Human and mouse	Backbone, four limbs, hair, milk for young	Close (both mammals)
Human and frog	Backbone, four limbs	More distant
Human and fish	Backbone	Most distant of the three

Diagram

A family tree of vertebrates

A family tree (phylogenetic tree) shows relationships as branches. Each branch point stands for a common ancestor. Features such as a backbone, four limbs, and hair and milk appear at the branch where they first arose and are shared by everything above that branch.

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