Evolution (video) | Khan Academy
Evolution is the process where heritable traits in a group of organisms change over many generations. This process is made possible by genetic variation. This variation, often resulting from sexual reproduction, leads to a range of traits within a population. Over time, small differences between organisms in a population can accumulate, leading to the evolution of new species.
Overview

Added
March 17, 2026
Subject & domain
life-health · evolution-natural-selection
Grade range
Grade 6–Grade 12 (Senior)
Page kind
Video
Introduction
Summary of Discussion: Evolution and Related Topics
- Evolutionary Mechanisms:
- Evolution describes how life changes over time, but it does not explain the origin of the first life.
- Asexual reproduction can drive evolution through mutations that occur during mitosis, even without the recombination found in sexual reproduction.
- Genetic traits (such as fingerprints) are unique to individuals, illustrating how specific variations persist within populations.
- Biological and Psychological Concepts:
- Emotions are a fundamental human trait rooted in brain function and biology; "emotional numbness" is distinct from a total lack of emotional capacity.
- Cosmology and Earth Science:
- Big Bounce Theory: A hypothesis suggesting the universe undergoes cycles of expansion (Big Bang) and collapse (Big Crunch).
- Earth Formation: The planet formed through the accretion of debris around the sun via gravity.
- Species and Adaptation:
- Many modern species (including insects, sharks, and various plants) are descendants of organisms that lived during the age of dinosaurs.
- Adaptation allows species to survive environmental changes, leading to the diversification of plant and animal varieties over time.
- There is an approximate 166:1 ratio of flying bird species to flightless bird species.
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