Speciation Requires a Barrier to Gene Flow

Lab Brief #5

🎯 Your mission

Understand the idea. Then look for it everywhere.

⚡ The twist

Nature loves to surprise the careful watcher.

What you'll learn

One population becomes two species when gene flow between them stops and selection then pulls the isolated groups apart. The barrier is often geographic — a new river, an island, a rising mountain range — and once separated the groups accumulate different mutations and face different pressures. They count as separate species when they can no longer produce fertile offspring, which is why horses and donkeys, whose mule offspring is sterile, are classified as two species rather than one.

Key words

gene flow
The movement of alleles between populations through interbreeding, which stops when a barrier isolates them.
speciation
The formation of a new species when isolated populations diverge until they can no longer interbreed successfully.

Make a hypothesis first

Before you start: write down what you think will happen, and why.

Say your guess out loud — then find out if you were right.

Step 1 of 4 · Read

Think about what you just learned: say what "gene flow" and "speciation" mean in your own words before you start.

Step 2 of 4 · Do

Map the Galapagos finch species against their islands and beak measurements, and mark where each population is isolated from the others. Write the sequence of events that turned one arriving population into several species.

Step 3 of 4 · Observe

Record what actually happened, including anything that did not match what you expected.

Step 4 of 4 · Record

Write a conclusion that answers the question this lesson opened with, and state your uncertainty.

Question 1 of 3

Speciation begins when two populations stop:

How sure are you?😐 maybe

Question 2 of 3

Horses and donkeys are counted as separate species because their offspring is:

How sure are you?😐 maybe

Question 3 of 3

The commonest first step toward speciation is:

How sure are you?😐 maybe

Mind = blown

🔬 The more you look, the more nature shows you.

Nice work!

You got 0 of 3 right.

All lessons

🎯

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✨ More to explore

🌍 Where you see this in real life: This shows up in your everyday life more than you'd think.

🏆 Stretch challenge (try it this week): Try one experiment in real life this week — even a tiny one.

👨‍👩‍👧 For the dinner table: “What's the most surprising thing you learned today?”

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Speciation Requires a Barrier to Gene Flow

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Speciation Requires a Barrier to Gene Flow

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