Natural Selection
Lesson notes
Overview
Individuals better matched to their environment leave more offspring, shifting the population. This topic is rated beginner and is number 12 of 110 in Biology. Core ideas and first intuitions. No prior knowledge needed.
What you are seeing
The panel above shows a living system animated over time. The animation is drawn live from the model, so everything you see responds to the sliders. Press Space to pause, use Restart to replay from the start, and change the speed to slow down quick events.
In depth
Natural selection operates when individuals in a population vary in heritable traits and some variants survive and reproduce more than others. Over generations the favoured traits become more common and the population shifts. Darwin and Wallace proposed it as the main mechanism of evolution. It acts on existing variation and has no foresight: it favours whatever works now. Examples include the beaks of Galápagos finches and the dark moths that spread in sooty industrial Britain.
Reading the relationship
The expression "fitness differences → change" is a compact summary of the idea. It uses the symbols f, i, t, n, e, s; name what each one stands for before you start. Then use the sliders to see how changing one quantity changes the others.
A guided exploration
1. Run the animation once with the default settings and describe in words what happens. 2. Change one slider at a time and note which quantity responds most. 3. Push each slider to its extreme and decide whether the result still makes sense.
Try this
Start by only moving one slider at a time. Say aloud what you expect, then check.
Common pitfalls
Biological processes are rarely all-or-nothing. Look for the feedback, the timing and the exceptions, rather than learning a single fixed sequence by heart.
How it connects
It builds on “The Hardy–Weinberg Principle”, the topic before it in Biology. Once you are comfortable, continue with “Adaptation to a Changing Environment”.
Why it matters
Biology shows how living things are built and how they work, grow, inherit traits and adapt.
Where you might use it
- Revising “Natural Selection” before a class, exam or certification
- Understanding inherited conditions, medicines and how the body responds to disease
- Working in farming, conservation and food production, where populations and genes matter
- Following news about vaccines, genetic testing and climate effects on wildlife
Frequently asked questions
What is Natural Selection?
Individuals better matched to their environment leave more offspring, shifting the population. It is a beginner topic in Biology.
How do I use the Natural Selection simulation?
The panel at the top shows a living system animated over time. Move the sliders one at a time, then press Space to pause the animation and look closer.
What does the formula mean?
The expression fitness differences → change packs the idea into symbols. Name each symbol first, then change one quantity with the sliders and see which others respond.
Who is this topic for?
Core ideas and first intuitions. No prior knowledge needed. If the quiz feels hard, reread the lesson notes and try the previous topic first.
What should I learn before this?
Start with “The Hardy–Weinberg Principle”, the previous topic in Biology. Each topic in a subject builds on the ones before it.
How do I track my progress?
Press “Mark as learned” on this page. Progress is stored only in this browser and is never sent anywhere. The Browse page can show topics you have learned or still need to learn.
Quick quiz
More in Biology
See all →Adaptation to a Changing Environment
Move the environment and watch the population’s trait distribution follow it.
Antibiotic Resistance
Antibiotics kill susceptible bacteria and leave resistant mutants to multiply.
Speciation
Populations isolated from one another accumulate differences until they cannot interbreed.