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Evolution is a change in the inherited characteristics of a population over time through natural selection. Free notes with key terms and 9 questions answered.
What is Evolution? is part of Variation and evolution in GCSE AQA Higher Biology.
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Evolution is a change in the inherited characteristics of a population over time through natural selection. Free notes with key terms and 9 questions answered.
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Use this lesson to stay inside Variation and evolution while connecting the detail back to the wider Inheritance, variation and evolution topic.
Read the core explanations from What is Evolution? before testing yourself from memory.
Why do giraffes have long necks? Why are polar bears white? These aren't random features - they're the result of evolution, one of the most powerful ideas in science.
Think of evolution like this: imagine a population of beetles. Some are green, some are brown. Over many generations, you notice more brown beetles and fewer green ones. The population has evolved - its characteristics have changed over time.
Trap: Many students think individual organisms evolve during their lifetime. Actually, populations evolve over many generations - individuals don't change their inherited characteristics.
Evolution doesn't happen randomly. There's a mechanism driving it: natural selection. This is where Darwin's genius shines through.
Natural selection works like a filter. Picture those beetles again: if birds find it easier to spot green beetles on brown tree bark, more green beetles get eaten. Brown beetles survive longer, reproduce more, and pass on their 'brown' genes. Over time, the population becomes mostly brown.
For natural selection to work, you need three key ingredients: variation (different characteristics), inheritance (traits passed to offspring), and selection pressure (something that affects survival or reproduction).
The theory of evolution by natural selection states that all species of living things have evolved from simple life forms that first developed more than three billion years ago. That's a mind-boggling timescale.
Imagine compressing Earth's history into a single year. Simple life forms appear in March. Complex cells don't show up until August. Animals with shells appear in mid-November. Dinosaurs rule for just a few days in December. Humans appear in the last few minutes of New Year's Eve.
This vast timescale is crucial. Small changes accumulate over millions of generations. A tiny advantage - running slightly faster, seeing slightly better, digesting food slightly more efficiently - compounds over time into dramatic differences.
Evolution doesn't just change existing species - it can create entirely new ones. This happens when populations become so different they can no longer interbreed to produce fertile offspring.
Think of Darwin's finches on the Galápagos Islands. Different islands had different food sources. Finches with beaks suited to their island's food survived better. Over time, each island's finch population developed distinct beak shapes. Eventually, they became separate species.
Worked example: How Natural Selection Creates New Species
Explain how a single ancestral species can evolve into multiple new species through natural selection.
Answer: Geographic separation leads to different selection pressures, causing populations to evolve different adaptations until they become reproductively isolated as separate species.
Evolution questions often trip students up because they confuse individual change with population change, or they forget the timescales involved. Here's how to nail these questions every time.
Exam depth extension: In what is evolution?, connect what is evolution? to the engine of evolution: natural selection using clear cause-and-effect statements. When you explain biological processes, include what changes, why it changes, and the consequence for cells, organisms, or populations. If calculations appear, show each step, include units, and end with a sentence that interprets the result in biological context.
Command word focus: 'Explain' questions want you to give reasons. Don't just describe what happens - explain WHY it happens using natural selection principles.
Notice how the sample answer follows the natural selection sequence: advantage → survival → reproduction → inheritance → population change. This structure works for any evolution question.
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
Evolution is a change in the inherited characteristics of a population over time through a process of natural selection, which may result in the formation of a new species. Populations evolve over many generations; individual organisms do not change their inherited characteristics during their lifetime.
Natural selection is the process by which organisms with characteristics that make them better adapted to their environment are more likely to survive and reproduce successfully, passing these advantageous characteristics to their offspring. It needs variation, inheritance and a selection pressure.
An adaptation is a characteristic that increases an organism's chance of survival and reproduction in its environment, developed through natural selection. For example, Darwin's finches on different Galápagos Islands developed beak shapes suited to each island's food.
Simple life forms first developed on Earth more than three billion years ago, and all species of living things have evolved from them. Small changes accumulate over millions of generations into dramatic differences.
The theory of evolution by natural selection states that all species of living things have evolved from simple life forms that first developed more than three billion years ago. Small advantages accumulate over millions of generations into dramatic differences.
Individual organisms do not evolve during their lifetime; populations evolve over many generations. For example, if birds spot green beetles more easily on brown bark, brown beetles survive and reproduce more, so over time the population becomes mostly brown.
Natural selection needs three key ingredients: variation, meaning different characteristics; inheritance, meaning traits are passed to offspring; and selection pressure, meaning something that affects survival or reproduction.
Beetles show natural selection when birds find green beetles easier to spot on brown tree bark, so more green beetles get eaten. Brown beetles survive longer, reproduce more and pass on their 'brown' genes, so over time the population becomes mostly brown.
The order of events in natural selection is: an advantage, then better survival, then more reproduction, then inheritance of the advantageous trait, then population change. This sequence works for any evolution question.