Lamarck vs Darwin – two theories of evolution tested
BiologyEvolutionAges 17–18
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Next in Evolution
Two giraffe herds evolve side by side from the same short-necked ancestors. Under Lamarck's rules every giraffe stretches its neck to reach the leaves and passes the stretch on; under Darwin and Wallace's natural selection necks already vary at birth and giraffes that reach more leaves leave more calves. Predict a calf's neck under each theory, test the inheritance of acquired characteristics against Weismann's tail-cutting experiment and evidence cards such as trained animals, then see how the modern synthesis explains variation with genes, alleles and random mutation.
Lesson: Theories of evolution: Lamarckism, Darwinism and the modern (neo-Darwinian) synthesis
What it shows
Lamarck explained evolution by use and disuse: organs grow when used, and the changes an animal acquires in its life pass to its young. Darwin and Wallace proposed natural selection: individuals already vary at birth, more are born than can survive, and those with useful inherited traits leave more offspring. Both explain long giraffe necks, so evidence must decide. Weismann cut the tails of mice for five generations and their young still had normal tails, and trained animals do not pass on their training. The modern synthesis adds genetics: variation comes from random mutation and the mixing of alleles.
How to use
In Two theories, set Leaf height and Variation at birth, press Run or Step and compare the herds, histograms and graph. In Predict the calves, enter both predictions in the task, then press Breed 20 calves. In Evidence, press Cut tails and breed and sort the evidence cards. In Genes and mutation, press Make a calf, change Mutation rate and tick Parents stretched their necks.
Parameters you can change
- View Two theories, Predict the calves, Evidence, Genes and mutation
- Leaf height 3.5–5.5 m
- Variation at birth 2–15 cm
- Mutation rate 0–5 %
Questions to explore
- Why do both theories predict longer necks, and what result could tell them apart?
- Why did Weismann's tail-cutting experiment count against Lamarck's theory?
- Where does new variation in neck length come from, according to the modern synthesis?
