Evolution — Part 2: Darwin, adaptive radiation and the mechanism of evolution: visual lesson, CBSE Class 12 Biology

Lesson

How evolution works

Part 2 — natural selection, adaptive radiation, and how population genetics measures evolution.

In this lesson you will

Explain Darwin’s theory of natural selection and compare it with Lamarck’s idea
Explain adaptive radiation and convergent evolution with examples
Apply the Hardy–Weinberg principle to calculate allele and genotype frequencies
Describe gene flow, genetic drift, mutation, recombination and three types of natural selection

Concept

Darwin and Wallace

Charles Darwin, on a sea voyage around the world aboard HMS Beagle, observed great variation among living forms and their fit to their environments. Alfred Wallace, working in the Malay Archipelago, reached similar conclusions.

Table of Darwin’s observations and inferences
Observation	Inference
Organisms produce more offspring than can survive	There is a struggle for existence
Individuals of a species vary	Some variants are better suited to the environment
Many variations are heritable	Better-suited variants leave more offspring
Over many generations	Populations change; new types arise (branching descent)

Concept

Natural selection and fitness

In Darwin’s sense, fitness means reproductive fitness: those who are better fit in an environment leave more progeny. Natural selection is the process by which such individuals increase in a population.

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