Doing Darwin’s Experiments Science educational resource Key Stages 3-4 Darwin Correspondence Project

Who was Charles Darwin? Born in Shrewsbury in 1809 Educated at Christ’s College, Cambridge Sailed around the world with HMS Beagle, 1831-1836 Became a famous gentleman- naturalist who published on many scientific topics Lived and worked at Down House in Kent Wrote the On the Origin of Species in 1859 which proposed the theory of evolution by natural selection Died at Down House in 1882 Copyright © Cambridge University Library

Where did Darwin do experiments? Darwin and his family lived at Down House in the village of Down (later Downe) in Kent. Between 1842 and 1882, Darwin conducted scientific experiments in and around his home – in the flower garden, kitchen garden, hothouse, orchard, meadow, and nearby woodland. Darwin walked and rode through the rural countryside around Down House observing the natural world. Darwin still had easy access to the heart of the British scientific community in London, around 20 miles away.

Where did Darwin do experiments? At Down House, Darwin worked in his study rather than in a typical laboratory. He wrote and received over 15,000 letters in his lifetime, corresponding with amateur and professional naturalists from Britain and around the world. Darwin used his correspondence to gather data about the natural world and used this data to construct his theories. Darwin wrote 15 books and 130 scientific papers while living at Down, including the On the Origin of Species. Darwin’s study. Copyright © English Heritage. By kind permission of Darwin Heirlooms Trust/Down House.

Experiment 1: Flytraps and Sundews Darwin was fascinated by insectivorous plants. He studied how they caught food, their digestion rates – even what they liked to eat! He used everyday materials like milk and egg white to test his ideas. He wrote: My book on Insectivorous Plants was published July 1875, that is sixteen years after my first observations. The delay in this case, as with all my other books, has been a great advantage to me; for a man after a long interval can criticise his own work, almost as well as if it were that of another person. The fact that a plant should secrete, when properly excited, a fluid containing an acid and ferment, closely analogous to the digestive fluid of an animal, was certainly a remarkable discovery.” – Charles Darwin (Autobiography, p. 132-33) Barlow, Nora ed. 1958. The autobiography of Charles Darwin 1809-1882. With the original omissions restored. Edited and with appendix and notes by his grand-daughter Nora Barlow. London: Collins.

Experiment 1A: Is it a plant or an animal? Drosera rotundifolia, Sundew Dionaea muscipula, Venus flytrap In groups, read through the letters and Darwin’s notes and answer the Understanding Letters questions. In pairs, list the features that define whether something is a plant or an animal. Share with the class. As a class, discuss which category an insectivorous plant fits into and why. What do they eat? Where do they live? How do they capture and digest their prey? Individually create a classification flowchart to describe this.

Experiment 1B: Design your own insectivorous plant Drosera rotundifolia, Sundew Dionaea muscipula, Venus flytrap In groups, read through the letters and experiments and answer the Understanding Letters questions. Based on your reading, design your own insectivorous plant. List all the special features that enable your plant to survive successfully and to reproduce.

Experiment 1C: How do insectivorous plants respond to the addition of different food types? In groups, read through the letters and answer the Understanding Letters questions. In groups, observe the state of your plant before the experiment. Add a sample of food to your plant. Observe how your plant reacts. Do the leaves close fully or partially? Do the tentacles change shape? Monitor these changes for seven days. Open the leaves and tentacles and remove the food remains. Observe the changes. Record your results and the state of your plant. Compare your results to Darwin’s findings. As a class, discuss why some results might be different and some might be the same.

Experiment 1C: How do insectivorous plants respond to the addition of different food types? Task Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7 (open up plant) Results Record: How has the plant reacted? Observe: What happened to the food sample? Additional notes:

Experiment 2: Survivor Seeds In the 1850s Darwin, unsatisfied by the traditional explanation that plants were designed to survive in one geographic location, started a series of experiments to test whether seeds could survive being soaked in salt water. While on the Beagle, Darwin observed very similar types of plants growing both on the mainland and on islands many kilometres away. Darwin thought that if seeds could successfully germinate after being in saltwater, then this would explain why island plants were similar to mainland plants. If these seeds were hardy enough to survive in saltwater, plants could be transported through the ocean to an island and then continue to evolve.

Experiment 2A: Salt water Seeds In groups, read through the letters and answer the Understanding Letters questions. Describe your seeds and predict which ones you think will survive the salt water. Why? Place the seeds in a small vial of salt water for 1 week. Monitor for one week. Record your findings. Plant the seeds in pots of moist compost. Observe the seeds every day for 2 weeks. Record results. Record the number of seeds that have germinated on a graph.

Experiment 2A: Salt water Seeds 4. Monitor for 1 week and record findings in table. Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7 Observations

Experiment 2A: Salt water Seeds WEEK 1 Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7 Seed type 1 Seed type 2 Seed type 3 Seed type 4 Seed type 5 WEEK 2

Experiment 2B: Digesting Seeds In groups, read through the letters and experiment notes and answer the Understanding Letters questions. Label each petri dish with the seed type and treatment type. Separate seeds into four piles and treat them as follows: Place one pile of seeds in the control petri dish Mix another pile into the gastric juices and pour both seeds and gastric juices into the gastric juices petri dish Crush several seeds with a hammer and place into crushed petri dish Place the final pile of seeds in the heated petri dish and place dish under/in a heat source Leave the petri dishes in their treatments for an agreed upon amount of time. Remove the seeds from their dishes and plant them in moist compost. Label pots with seed type and treatment. Monitor every day for 1-2 weeks. Record your results and share with the class. Which types of seeds germinated best in which conditions? Darwin’s ‘Experiment Book’. Copyright © Cambridge University Library

Experiment 2B: Digesting Seeds WEEK 1 dd/mm Control Gastric juices Crushed Heated

Experiment 2C: Owl Pellet Dissection In groups, read through the letters and Darwin's notes and answer the Understanding Letters questions. Break owl pellet in half onto white paper, then into smaller pieces. Carefully extract the pieces of bone and any plant material or seeds that you find. Identify the contents of the pellet – plants, seeds and animals. List your findings. Plant the seeds in small pots of moist compost. Label with as much information as possible. Monitor at regular intervals. Record your results. Darwin’s ‘Experiment Book’. Copyright © Cambridge University Library

Experiment 2C: Owl Pellet Dissection Seed Pots dd/mm 1 2 3 4 5 6

Experiment 3: Create a Weed Garden Working from his home at Down House in Kent meant Darwin was studying nature on his doorstep. He conducted all his experiments from Down. Darwin’s garden was the site of scientific experiment. In 1857 he cleared a small patch of ground to watch the progress of emerging weeds over a period of time. He was surprised at the number of seedlings that came up and marked each with a wire. Darwin carefully monitored their growth and was even more surprised at how few survived.

Experiment 3A: Weed Garden Progress Log In groups, read through the letters and Darwin's notes and answer the Understanding Letters questions. As a class, discuss how the seeds might arrive in your weed garden and what might be the factors influencing their survival. In early Spring prepare the plots of land by clearing any annual or perennial plants. Or put the prepared compost in a large seed tray (ensure tray has drainage holes). Place tray in a sunny position outside and keep soil moist. Wait 2 weeks and then observe and log any progress. Place a coloured wire in the spot where seedlings emerge. Use an identification chart to identify as many weeds as possible. Record your findings. Note the number of seedlings, date that they germinated and the numbers/ percentage survival rate at designated intervals. Check your seedlings regularly, removing any wires as a seedling dies. Update your records. What factors impacted the survival of weeds on your garden? Darwin’s ‘Experiment Book’. Copyright © Cambridge University Library

Experiment 3A: Weed Garden Progress Log Record dd/mm Number of seedlings Germination date Survival rate* *To calculate the survival rate: (number of seedlings on dd/mm) x 100 / (total number of seedlings first recorded)

For more educational resources: Please visit the Darwin Correspondence Project’s school resources pages: http://www.darwinproject.ac.uk/schools Do you have feedback? We would love to hear from you! Contact: darwin@lib.cam.ac.uk