Life changes over time: Biodiversity exists because life evolves. Evolution slowly builds new features, and in time new species.
The points to remember
- Evolution is cumulative change in the heritable characteristics of a population or species.
- Heritable: passed from parents to offspring in their genes, e.g. the shape of a beak.
- Cumulative: small changes add up over many generations.
- Populations evolve, not single animals: an individual cannot change its genes.
- A change gained in one lifetime (big muscles, a scar) is not heritable, so it is not evolution.
Remember it as: Heritable, cumulative, population: evolution in three words.
Real example: in 1977 a drought hit Daphne Major, a small Galapagos island. Small, soft seeds ran out, so finches with deeper beaks, able to crack big hard seeds, survived best. Their chicks inherited deeper beaks: the next generation's beaks were about 4% deeper on average.
Not evolution: A horse that gets fitter with training, or a plant that grows taller with fertiliser, has not evolved. The change is not in its genes, so it is not passed on.
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Over millions of years, evolution splits one species into many. Every living thing shares one common ancestor.
The points to remember
- Over long periods, evolution produces new species: this is where biodiversity comes from.
- All living things share one common ancestor, from at least 3.5 billion years ago.
- One species reaching a place with empty niches can split into many: adaptive radiation.
- Each new species suits a different food or habitat, so species diversity rises.
- Species also go extinct: today's biodiversity is new species formed minus species lost.
Real example: a finch-like bird reached Hawaii about 5 million years ago. Its descendants became more than 50 species of honeycreeper: seed-crackers, nectar-drinkers with long curved bills, and grub-diggers. This is adaptive radiation.
Link evolution to biodiversity: Say the link in full: 'evolution produces new species, so species diversity increases'.
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Evolution adds to all three levels of biodiversity: genetic, species and habitat.
The points to remember
- Genetic diversity is the raw material: evolution needs differences between individuals.
- Evolution turns those differences into new species: species diversity.
- Living things build and change habitats (reefs, forests), adding habitat diversity.
- More biodiversity gives more ways to cope with change: higher resilience.
Remember it as: Genes vary, species split, habitats grow, systems cope.
Genetic
- Finches on one island differ in beak depth.
Species
- About 18 species of Darwin's finch, from one ancestor.
Habitat
- Cactus finches depend on cactus scrub, a habitat that cactus species built.
Real example: Darwin's finches show all three levels: variation in beaks within one species, about 18 species across the Galapagos, and each species tied to its own habitat and food.
From evolution to resilience: For a longer answer, carry the chain on: evolution creates species, speciation raises biodiversity, and higher biodiversity makes ecosystems more resilient.
How this comes up: Paper 2, Section B (a): outline, with a named example, how evolution produces biodiversity [4].
The Galapagos Islands are home to about 18 species of Darwin's finch, all descended from one ancestor that arrived from South America.
Outline how evolutionary processes have produced this biodiversity.
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