How plants use humans to disperse themselves

Posted on 17 July 2013

There’s a carved wooden box in my office that holds a rainforest in waiting. People who open it gasp at the beauty within. The forest may have a long wait – conditions in the box are not to the liking of the hard-shelled seeds that range from small, polished mahogany nuts to shiny, golf-ball-sized brown pods.

They all come from the mouth of the Congo River where I found them while trying to discover a way across the vast waterway. Their origin was deep in rain-drenched central Africa where natural selection has favoured trees that use water dispersal for their seeds. They have tough shells, float well and are patient.

Other species don’t use water to disperse across the planet, they use us. And they’re so common and ever-present we’d be surprised to realise their presence is a strategy. But first it’s worth asking why things need to disperse.

The further you travel as a species, the greater your chances of survival because of an ever-widening range of habitats that might prove beneficial. The point of the ingenious seeds in my wooden box is a mixture of crowd avoidance and the search for greener pastures. The key to their success is not intention but a never-ending series of accidents, culled by natural selection until the result is so effective or beautiful that it seems to be a miracle of purpose.

Take lemurs on Madagascar. The accident that got them there would have occurred around 65 million years ago when a huge cyclone ripped through the tropical forests of East Africa, throwing down trees, ploughing up river banks and disgorging huge rafts of debris into a prehistoric ocean.

Aboard one of the rafts would have been a family of small creatures, rather like bushbabies, disturbed in their hibernation by the ruckus but soon settling down within their floating tree trunk. Eventually their tree would have washed up on a beach and they became the first vertebrates to colonise their new world absent of predators.

For millions of years life-supporting rafts of greenery or even volcanic pumice have sailed the oceans and still do, birds and insects are blown off course by storms and colonise distant islands, seeds drift down rivers or in the wind, sometimes for years, before breaking open and putting down roots in foreign soil. All over the planet, one way or another, life moves and thrives.

Recent research, however, has shown that dispersal and survival is far more sophisticated than ocean currents, freak storms and chance green pastures. Plants and creatures take whatever gaps they can find and, increasingly, we are the unwitting pawns in their game.

Humans have hugely altered the planet’s environment, cutting down forests, hunting wildlife, planting crops and building cities. We’re the most populous of vertebrates, are immensely destructive and extremely useful, depending on the adaptability of your genetic make-up. We use a vast number of species essential for our survival. Recently, science writer Michael Pollan turned that idea on its head. He wondered what was using us for its survival and started looking for answers. The result was surprising.

At a genetic level, all a species cares about is making copies of itself and thriving. Many fight for that space with thorns, teeth, claws and poisons. But some have learned the trick of co-operation. Which animal is more successful and more widespread, the dog or the wolf, the domestic cat or the lion, the cow or the kudu, the chicken or the guineafowl, wheat grass or a forest?

‘It makes as much sense,’ says Pollan, ‘to think of agriculture as something the grasses did to people as a way to conquer trees.’

The genetic mutability of the dog, descended from a single wolf species (grey wolf), allowed us to turn it into everything from a Great Dane to a Pekinese and desire it. The same strategy transformed a tree with indifferent, sour fruit into a lusty, sweet apple; an obscure South American root into a large tuber capable of producing crispy, golden potato chips.

You can’t credit a plant with intelligence, but long before we were refining consciousness and learning to walk on two feet, they were developing photosynthesis (the astonishing trick of converting sunlight into food) and perfecting organic chemistry. Plants can’t move, so they use creatures to move for them by providing nourishment and useful chemical cocktails. Why else would they go to all the trouble of devising recipes for so many complex molecules – and affording the energy needed to manufacture them – if not to entice creatures like us to do their bidding?

For what other reason would they produce the precise chemicals we need to heal us? To what other end would they concoct the perfect combination to hit our pleasure zones, getting us to love wine or whisky or beguile us to take a scrappy plant like cannabis and spread it all over the world, nurturing and developing it into a cognitive mind bomb like skunk? Using the Earth’s most powerful predator to please, protect and disseminate you has to be as close to intelligence as natural selection will allow.

My box of seeds is clearly biding its time. Sooner or later someone, if not me, will value the carving but not the contents and toss the lot into a bin or, better, a compost heap far from the Congo. Humans will yet again have committed the sin of introducing alien species to an environment. But the seeds won’t mind. The time spent in the box will be justified, the forest’s wait will be over and, just maybe, their dispersal strategy using humans will have succeeded. Time is on their side.

If you’d like to try a personal dispersal to see the lemurs of Madagascar, Jenman Island Safaris (www.travel2madagascar. com) organises great adventure travel.




yoast-primary -
tcat - Environment
tcat_slug - environment
tcat2 -
tcat2_slug -
tcat_final -