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What brainless moulds may teach us

Date: September 04 2010

Deborah Smith

These single-cell organisms somehow make decisions we associate with humans, writes Deborah Smith.

It's an irrational quirk of human nature that clever businesses can easily exploit. If people are offered two choices, for example two bottles of wine at a restaurant, one $30 and the other $50, the lower priced one looks like the best buy. Yet if a third very expensive option, say a $500 bottle, is also available, consumers are more likely to decide that the mid-range choice, the $50 bottle, is an attractive deal.

Value for money has not changed, nor has the amount of cash in people's pockets. So switching preferences is economic folly, says Dr Tanya Latty, a biologist at the University of Sydney.

But we are not alone in succumbing to this lack of logic. Latty and her colleagues have found we share the irrational behaviour with slime moulds - single-celled, brainless creatures that ooze their way across the forest floor in search of food.

These amoeba-like blobs cannot only help reveal why we think the way we do. They could also teach us how to solve complex puzzles, design efficient railways and build better computer and phone communication networks.

Slime moulds, which can be found in many Sydney backyards, are about as different from people as you can get. We last shared a common ancestor more than a billion years ago.

''They are just big, slimy balls of goo. But they can also do things that far exceed what you'd expect from something with no brain,'' Latty says.

Her research has shown these mindless organisms can weigh up benefits and risks in a sophisticated way when seeking out food.

Moving at up to five centimetres an hour, they forage by producing a sprawling network of branches that thicken or retreat according to what they find.

Light can dry them out, so they avoid it. ''They take mood lighting one step further than us and prefer to dine in the dark,'' she says.

So Latty offered slime moulds, Physarum polycephalum, two choices of food, made from different strengths of oatmeal, placed in the dark or the light.

They were not stupid. ''When both food patches were shaded, 100 per cent of our slime moulds made the decision to grow towards the better quality meal,'' she says.

But if the two food samples were close in quality the blobs stuck with the safer option, the patch in the dark.

There was also a tipping point for the slime. When there was a big difference in food quality, they were prepared to venture into the risky, well-lit territory to get the better meal.

''It shows they are capable of making really complicated foraging decisions,'' says Latty, whose study with Associate Professor Madeleine Beekman was published in the journal Ecology.

The team then wondered how the slime moulds would react to a third choice, and were surprised to find they were irrational, like humans.

Given a choice between 5 per cent oatmeal in the light and 3 per cent oatmeal in the dark, the cells fed on each option equally.

But when a third, inferior meal was offered, 1 per cent oatmeal in the dark, they switched and were much more likely to choose the middle, 3 per cent, option.

Latty says our irrational decision making was thought to be due to the way our brains process information, or because we get emotionally attached to things. But the slime mould finding, published in the Proceedings of the Royal Society B shows that the behaviour is much more basic, and goes back a long way in evolutionary history.

''It tells us that it is not just a quirk of our brains,'' she says.

It shows people and slime moulds make a rough comparison across options, rather than working out the absolute value of each one.

The benefit may be speed. We assume that irrationality is bad, she says, but when hunting for food, a quick decision could be life saving. ''If you're slow, there is actually a penalty. Something might eat you, or you might get injured. So in some situations it might be better to make a fast decision that is good enough, rather than a perfect decision that takes a long time.''

One of the reasons for studying these very basic creatures is to learn from billions of years of evolution how to program computers to design better technological systems.

This year a Japanese and British team showed slime moulds can produce a network almost identical to Tokyo's rail system. The researchers placed oat flakes at sites that corresponded to the cities surrounding Tokyo. The slime mould grew from the centre and developed a web of connections with the scattered food sources.

The final pattern was as efficient, reliable and cost effective as the real rail network, the team reported in the journal Science.

By developing mathematical models based on how the slime mould solved the problem naturally, the researchers hope to develop biologically inspired ways to improve self-organising systems, such as arrays of remote sensors and wireless networks.

The Sydney team, which includes Chris Reid, is also studying how slime moulds tackle mathematical puzzles, such as the Tower of Hanoi game, in which stacks of different sized discs have to be rearranged. The problem can be translated into a two-dimensional one where the cell can use its skill at finding the most efficient network between food sources.

Working out how humans solve even simple problems with their complex brains filled with billions of neurones is very difficult, Latty says.

''But with slime moulds we might have a chance.''



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