A Prediction Experiment

The Best Fit

Why do animals end up so perfectly suited to where they live? Today you'll learn how nature "chooses" — then you will predict which beetles survive over many generations.

Before we start — a polar bear is white and a forest frog is green — how do you think animals end up matching where they live?

A population has variation

No two individuals are exactly alike. In our beetle population, some are born green and some are born brown. This natural variation is the raw material for everything that follows.

Quick check, together: If every beetle were exactly identical, could natural selection have anything to "choose" between?

Answer: No — with no variation there's nothing for selection to favour, so nothing would change.

The environment selects

A hungry bird spots the beetles that stand out and eats them first. The ones that blend in are more likely to survive. This is the "survival of the fittest" — fittest means best-suited, not strongest.

Quick check, together: On green leaves, which beetle is more likely to be eaten — the green one or the brown one? Why?

Answer: The one that stands out against green is more likely to be eaten.

Survivors pass it on

The survivors have babies — and pass on their colour. So each generation has more of the well-camouflaged kind. Over many generations, the whole population adapts to fit its home.

Quick check, together: Name the three ingredients selection needs: variation, a survival ______, and passing traits to ______.

Answer: Variation, a survival advantage (the pressure), and passing traits to offspring (heredity).

How does life come to fit?

Nature keeps whatever fits best.