Destination Space

DNA, Evolution and Extinction

How has life survived for 3.7 billion years?

Session Plan
The full session, stage by stage: what to say, what to do, and what to expect from the students.
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Slide Deck
Everything you'll put on the board, in order. Speaker notes included.
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ITZA Pathways
One link covers everything for this session: both pathways, the minigame for early finishers, and the extension activities.
- Session 8 (opens in a new tab)
Learner Journal
The five-part reflection learners complete in the plenary of every session.
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Explain how RNA solved the chicken-and-egg problem of early life, how DNA became the permanent instruction manual inside cells, and how DNA, RNA and proteins relate.
Explain what LUCA is and why scientists believe all life descends from it.
Define mutation and explain how copying mistakes in DNA drive evolution.
Describe the five mass extinction events and explain why biodiversity helps life survive them.
Apply the principles of flexibility, population spread and genetic variation to predict which species would survive a catastrophic event.

Evolution is a single big mutation turning one animal into a new species overnight.
Evolution is the accumulation of many small copying mistakes over millions of years and millions of individuals, not one dramatic event.
The most specialised or strongest species survives.
The opposite is often true. Generalists, species that can eat varied food, tolerate a range of climates, and exist in many places, tend to survive sudden change better than highly specialised species.

Isn’t evolution just DNA copying itself?: Accurate copying is actually the opposite of evolution. It is what keeps species the same. Evolution happens because of the rare mistakes that creep in.
If a species has survived mass extinctions before, is it safe from the next one?: A species that has existed unchanged for millions of years (a “living fossil”) is not automatically safe. If the conditions that made it successful disappear, its long track record offers no protection.

It helps to let the paradox in the cookies analogy land before you move on to DNA: a cook needs a recipe, but recipes don’t write themselves, so someone had to bake cookies first for a recipe to exist. It’s worth leaving it unresolved for a moment before connecting it to DNA and protein.
You might make the DNA and protein link explicit: DNA needs proteins to copy itself, but proteins need DNA as their recipe. That circular dependency is the whole point of the session, so it’s worth stating twice.
If a learner asks “Which came first?”, it helps to ask them to hold that question. The pathway has a genuinely satisfying answer.

On Pathway 1, you could ask learners to explain in one sentence why RNA solved a problem DNA alone couldn’t. If they can’t, that’s the one to go back to.
On Pathway 2, “What connects a single DNA copying mistake to a mass extinction millions of years later?” is worth asking. It’s a big jump in scale, so it’s worth pausing on.
“Which fact surprised you most?” works well here too.

Thumbs up or down works for a general read of the room, and mini whiteboards give you an individual check if you have them. Use whichever suits your class.
It helps to cold call for justification before confirming each answer. The reasoning is the point, not just the verdict.
The last three traits are built to catch a specific shortcut: being the best at one thing, surviving unchanged for millions of years, or being highly adaptable. None of these guarantees survival alone, so you might push learners to weigh flexibility, spread and genetic variation together.
The “50 individuals, highly adaptable” case usually splits the room, so it’s worth not rushing to resolve it. Small numbers mean low genetic diversity, and one disaster can wipe out the whole population regardless of adaptability.

It helps not to rush learners past the 99.9% figure. Give them the full two minutes of silence before opening up discussion.
It helps to keep this part calmer than the activity.
The lock-in is from Charles Darwin, the naturalist who developed the theory of evolution by natural selection. Naming him adds weight, because this isn’t a general observation, it’s from the man who worked it out.

Extension 1
The Theory of Evolution
The most famous theory of evolution came from Charles Darwin, after a voyage around the world that made him see life in a whole new light. What did he see?
Explore(opens in a new tab)
Extension 2
Evolution’s Strange Inventions
Cut off from the mainland, Madagascar produced some very strange residents. Discover how its isolation shaped two remarkable species.
Explore(opens in a new tab)

Biology: The role of cells in different organisms. How information in the genome is expressed as proteins and how mutations alter protein structure. The structure and function of DNA and how characteristics are inherited.
Science & Evolution: The scientific process of natural selection and how organisms adapt and evolve. Genetic variation as a survival advantage. The fossil record and the Big Five mass extinctions.
History of Science: How scientists infer the existence of LUCA without any fossil evidence, by comparing shared genes across species.
Maths: Working with very small probabilities (one mutation per billion DNA copies) and very large timescales (3.7 billion years).
English & Literacy: Evaluating evidence and forming a reasoned argument about which species traits matter most for survival.