Nature Studies by Michael McCarthy: A toxic question on mushrooms
Friday 22 October 2010
Why are some mushrooms poisonous? I must admit the question had never occurred to me until last weekend, when it suddenly thrust itself into my consciousness in the middle of a mushroom-gathering expedition in France. We were in Bellême in southern Normandy, a small hilltop town which is bidding fair to be France's wild mushroom capital: every autumn it hosts a four-day national mushroom festival centred on the nearby Bellême forest, 6,000 acres of exquisite oak woods where fungi grow in astonishing profusion.
We were a week too late for the festival, but we had joined a mushroom outing organised by the local mycological club (mycology being the study of fungi). In Bellême's Place de La République we met Claude Charlemagne, the sprightly 72-year-old club chairman, who led the 50 of us who turned up, old and young, in a convoy of cars deep into the forest. And there, before we began the business of gathering, was the business of instruction.
We had to be, M. Charlemagne said, very, very careful. As part of the €2 ticket we had been given an excellent colour guide entitled "Mushrooms, toxic and edible – the confusions to avoid" and M. Charlemagne spelled out that if you did not avoid these confusions, and mistook toxic for edible, you were likely to end up very sick, on a dialysis machine for life, or perfectly possibly, dead. In particular he mentioned a mushroom which in French was the amanite phalloïde and which, he said, you will eat only once. (I looked it up when we got back: it was the death cap.)
The floor of the forest was packed with fungi – the first I encountered were fly agarics, the red-and-white-spotted toadstools on which garden gnomes sit while fishing, and these were the biggest and brightest I had ever seen – but the real treasures for which people were hunting were cèpes. Cèpes are among the meatiest and most delicious of wild mushrooms, fairly easy to identify because the white stalk is immensely fat, fatter than the brown cap, yet even cèpes can look like some toxic things, and as we spread out through the sun-dappled autumn woodlands scanning the leaf-litter under the oaks and beeches, it suddenly struck me as very strange that any mushrooms should be toxic at all.
I mean, why had they evolved to be like that? What was the pay-off, in evolutionary terms? You can see why some creatures employ poison: snakes and scorpions and spiders use venom to overcome their prey and in self-defence; while some butterflies are toxic so that they will not be eaten by birds, and they usually advertise their toxicity in bright warning colours. But some things have been designed by evolution to be eaten, fruits in particular: the pay-off they receive is that this way the seeds inside them are spread. (If you look at hawthorn bushes multiplying across a landscape, they have been spread by birds which have eaten the berries and pooed out the seeds.) Presumably mushrooms can be spread in the same way: the spores are dissipated with the digestion of the creature that eats them. So why should some of them be capable of killing the eater?
My own very amateur thinking about evolution has generally been that there is a reason for everything. This is known as the adaptationist position: that most if not all of the features of an organism are evolutionary adaptations to enable it to survive better. Nothing is accidental. But when I broached the subject of poisonous mushrooms with one of Britain's leading mycologists, the naturalist Peter Marren, last week, he instantly said: "It's an accident of biochemistry." Fungi don't have stomachs, he explained, but they can consume very tough objects like wood or minerals by breaking them down with a powerful arsenal of biochemicals which are not found in other parts of the natural world, and reabsorbing them. We might react badly to some of these chemicals, but it was possible, he said, that poisonous mushrooms were poisonous only to us. "You often see a death cap which has been nibbled by something; for all we know other animals can eat them with impunity."
I began to realise that there were more accidents in evolution that I had considered before. This, very approximately, was the position of the American Stephen Jay Gould in his heated Darwinian disputes with Richard Dawkins: if there's an evolutionary reason for everything, maybe there's an evolutionary reason for the hunger for private property, say, for aggression, even for rape; and it's only short step from saying, evolution is responsible for these aspects of human behaviour, to saying, evolution sanctions them. Yet perhaps quite a lot of things have happened in evolution, without a reason.
So I am more aware of accidents now and less of an a naïve adaptationist than I was, thanks to a dreamy autumn afternoon in the forest of Bellême in the company of M. Charlemagne the mycologist, an afternoon which finished with five fat cèpes in our basket, four of them, I have to confess, M. Charlemagne's generous gift. We brought them home, diced them, sweated them in a little boiling water, then fried them with chopped garlic; they were delicious, and we lived to tell the tale.
Why we should bring the quince back home
Another sign of autumn across the Channel: the appearance in the shops of quinces. We hardly know them – a great pity, as these apple-relatives, which look like giant misshapen lemons, have an intense perfume, something between the scent of oranges and the scent of passion fruit, which will fill a kitchen if you leave them out in a bowl, as we have done with the half-dozen quinces we brought back, along with the cèpes.
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