Charles Darwin spent many years experimenting in his garden and house, to build up evidence for his theory of evolution by natural selection. Try your hand at eight of his classic experiments.
Read our review of the new TV series looking at Darwin’s experiments
Guided by the light
Darwin noted that plant shoots emerging from the ground were sensitive to light and bent towards the sun as it crossed the sky. Keen to find out how the plants managed “directed” movement, he and his son Francis experimented.
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You will need:
- Plant pots
- soil
- seeds (Darwin used canary grass, Phalaris canariensis)
- aluminium foil
- a lamp
Sow the seeds in pots. When the shoots emerge, switch on the lamp and watch them grow towards it. Repeat, but this time pop a foil “hat” securely over the tip of the shoot before switching on the lamp.
Darwin worked out that the upper part of a shoot is necessary for the plant to respond to light: this paved the way for the discovery of hormones.
Hungry plants
Just after the publication of On the Origin of Species, Darwin was on holiday in the neighbouring county of Sussex when he stumbled upon the tiny insect-eating plant Drosera rotundifolia or sundew. This inspired him to mount a series of detailed experiments to discover its preferred diet.
You will need:
- A sundew plant
- pretty much any food you like
Darwin tested the sundew’s appetite for a vast array of different foods, including milk, oil, egg white, gelatin, sugar, hair, toenail clippings and even drops of urine. Make up your own morsels to discover what the plants like and dislike. Darwin’s conclusion was that they were seeking out nitrogen.
If you can’t get hold of a sundew, you might try experimenting with a venus flytrap to see what triggers it to shut.
Dying young
Darwin set up his “weed garden” experiment in January 1857, but if you set about this soon you’ll still get good results.
You will need:
- A tape measure
- four pegs
- a hammer
- a ball of twine
- a spade
- a ball of garden wire snipped into 5-centimetre lengths
Use the pegs and twine to mark out a plot of lawn (1 metre by 0.7 metres) and carefully remove the layer of turf to expose the soil. Return every day to check for signs of germinating seeds, sinking a small length of garden wire next to each emerging shoot and collecting up (and keeping) wires where seedlings have died. Come summer, work out the extent of death on your patch. Darwin found that more than 80 per cent of his weedlings died young.
A seed of an idea
Back from the Beagle, Darwin pondered how plants and animals reached all the corners of the Earth. Conventional wisdom was that God put them there, but Darwin had other ideas. Perhaps seeds survived at sea and used ocean currents…
You will need:
- Seawater (most pet shops sell salt water)
- glass jars
- your choice of seeds
- a sieve
- plant pots
- compost
Darwin used seeds of cress, radish, cabbages, lettuces, carrots, celery and onion. Label jars, fill with seawater and your seeds. After seven days, put the seeds in a sieve, rinse under a tap, and plant out in labelled pots. Darwin also studied longer periods in seawater, the effects of water temperature on germination, and whether seeds float. His experiments overturned the idea that seawater kills seeds. Of the 87 species he used, Darwin found almost three-quarters could tolerate at least 28 days in salt water.
The price of competition
In his “lawn experiment”, conducted in 1856, Darwin staked out a plot of old lawn and gave the gardeners strict instructions not to touch it. By mid-summer, once overgrown, it stood out in stark contrast to the lawn around it. “[O]ut of twenty species growing on a little plot of turf (three feet by four) nine species perished from the other species being allowed to grow up freely,” he wrote in the Origin.
You will need:
- A tape measure
- 4 pegs
- A hammer
- A ball of twine
Hammer pegs into a patch of lawn to create a plot about 1 square metre. Wind twine around the pegs to make the plot abundantly clear to others. Get down on your knees and count the number of different plants growing in the plot. Count them again when thoroughly overgrown. In a competitive scenario, the tougher species will fare better than others.
A deathly experiment
Darwin set up his “weed garden” experiment in January 1857, but if you set about this soon you’ll still get good results.
You will need:
- A tape measure
- 4 pegs
- A hammer
- A ball of twine
- Spade
- A ball of garden wire snipped into 3 cm lengths.
As with the “lawn experiment”, use the pegs and twine to mark out a plot of lawn (this time 3 feet by 2 feet) and carefully remove the layer of turf to expose the soil. Return every day to check for signs of germinating seeds, sinking a small length of garden wire alongside each emerging shoot and collecting up (and keeping) wires where seedlings have succumbed. Come summer, work out the extent of death on your patch. Darwin found that more than 80% of his weedlings never made it into mature weeds.
Ant attack
Whilst at a spa in 1858, receiving treatment for one of his many ailments, Darwin performed a series of experiments on ant communication.
You will need:
- An empty jam jar or other suitable vessel for transporting ants
- Ants from two different nests
Provided it’s the right time of year (late spring and early summer), ants should be pretty easy to come by. Chances are you won’t end up experimenting with the species Darwin stumbled upon (Formica rufa) but the important thing is that you locate two different colonies of the same species. Usher a few ants from colony A into a jam jar and carry them over to colony B. When Darwin performed this crude experiment, he found that the ants from one nest “pitch unmercifully into a stranger brought from another”. From this, he correctly concluded that ants can sense and respond to chemical cues that differ between colonies. Repeat until you get a niggling feeling that you’re torturing ants. You are.
Pollination power
Because it is not capable of self-fertilization, clover will not set seed without assistance from insects, making it a suitable common flower with which to explore co-evolution of two rather different species. Darwin studied red clover although you are more likely to come across the white variety.
You will need:
- Several clumps of clover
- A mesh to deny bees access
Before your clover comes into flower, seal several clumps beneath an insect-proof mesh. At the end of the season, compare the number of seeds produced by covered and uncovered flowers. Darwin found that the ones under the mesh failed to produce seed heads, whilst those out in the open did very well.
Read our review of the TV series looking at Darwin’s experiments
