杏吧原创

Jimmy Doherty in Darwin鈥檚 Garden BBC 2 in the UK, 5 March at 8 pm

Try your hand at eight of Darwin鈥檚 experiments

CHARLES DARWIN鈥檚 penchant for experimentation was obvious from an early age. Growing up in Shrewsbury, near the border with Wales, he and his brother Erasmus 鈥淩as鈥� played with chemicals, earning Charles the nickname 鈥淕as鈥�. And during the Beagle voyage, when he stumbled upon a line of Andean condors, the 20-something Darwin couldn鈥檛 resist an experiment into vulture olfaction, wrapping up a hunk of fresh meat and tossing it to the birds, only to have them totally ignore the rich whiff of fresh meat. Condors, he concluded, probably rely on vision to hunt.

But it was at Down House in Kent, his home from 1842, that Darwin really settled into his experimental rhythm. English Heritage, now the custodian of Down House, has been working to bring to life many experiments Darwin set up in his garden and, sometimes, the house. These offer an insight into Darwin鈥檚 way of working and help to explain how, with only a garden, great curiosity and imagination he transformed the way we see the natural world.

In March, the BBC TV series Jimmy Doherty in Darwin鈥檚 Garden will introduce British viewers to Darwin the experimentalist, as Doherty re-enacts a selection of Darwin鈥檚 investigations. Among them are the seawater experiments with which Darwin set out in 1855 to discover whether seawater kills seeds. He feared this question might 鈥渁ppear childish鈥�, but instead it produced intriguing results and unexpectedly profound conclusions.

Darwin wanted to know if it was possible for seeds to survive at sea: if they could, ocean currents might carry them to new lands, thus accounting for the plant distribution he had seen during his Beagle days.

Doherty recreates one of these seed-salting experiments and finds seeds do survive salt. Darwin began with cress, radish, carrots, cabbages, lettuces, celery and onion, at first leaving seeds in salt water for a week before planting out. They all germinated, some more convincingly than others. Only after this success did Darwin try longer periods 鈥� such as the month in Doherty鈥檚 version. The conclusion is clear: plants that tolerate a month at sea, as many can, could travel the world.

There is also the 鈥渨eed patch鈥� experiment, capturing the role of death in natural selection. In January 1857, Darwin stripped turf from a patch of lawn, which he monitored daily for germinating seeds, sinking a wire to mark each emerging shoot. By the end of spring, just 62 of 357 seedlings survived the trials of early life, such as slugs, but those survivors had a hardiness which, if passed on, would help explain how species evolve over generations.

Not all of Darwin鈥檚 experiments are easy to reproduce, and some were 鈥渢hought experiments鈥�. When, for example, one correspondent reported field mice destroying bees鈥� nests, Darwin was first to propose what we now call a food chain: cats have an impact on the number of mice, which have an impact on the bees, which have an impact on pollination.

Doherty has a stab at testing the prediction that hives located away from cats will be more prone to mouse depredation than those where cats are abundant. This is great TV but poor science, and the pitifully small sample yields predictably inconclusive results. Darwin didn鈥檛 test this link in the chain; perhaps he anticipated the difficulties Doherty encounters. But he did devise an experiment to test whether bees were needed to fertilise clover, using mesh 鈥� made from his wife Emma鈥檚 old petticoats 鈥� to deny insects access to flowers in one of his meadows.

With only three episodes to cover a life鈥檚 work, the programme makers were forced to cherry-pick, but they could have done more to acknowledge the large number of experiments left out. When it came to seed-salting, for example, Darwin didn鈥檛 just pop six species in salt water, he ran dozens of experiments. When his seeds sank it seemed to pose 鈥渁 fatal obstacle鈥� to ocean distribution. So he investigated seed buoyancy. If really dry, many seeds will float.

鈥淲hen Darwin鈥檚 seeds sank, it seemed to pose a fatal obstacle to the idea of ocean distribution鈥�

Though we get only a slice of Darwin the experimentalist, Doherty is an enthusiastic presenter, interspersing daily life at Down with vignettes about Darwin鈥檚 experiments on orchid sex, the diets of carnivorous plants, worm intelligence and human emotions.

One of the charms of the Down House experiments is the way Darwin used common or garden species and household items, and frequently involved members of his family. Re-enacting them is a fantastic way for us all to find out where scientific inquiry can lead 鈥� and it offers a unique insight into the influential and honest Darwin. We have four experiments here, and there are more online.

Try your hand at eight of Darwin鈥檚 experiments