WHEN I was young I knew an old woman, Nell, who lived alone except for her dog Spot. She loved that dog. And with good reason for, according to Nell, the dog was very wise.
He could foretell the weather and he was an unerring judge of character. He never warmed to a shiftless character or to a nasty one, but he was very appreciative of a good person.
I had no problem with her assessment as to the dog's insight in the latter regard. Spot was always very fond of me.
But what aroused my particular interest about this dog was his medical/nutritional knowledge. According to Nell, Spot ate only foods that were good for him.
When she bought meat from the butcher, she had a habit of leaving a piece of the raw meat out the back for Spot. On one occasion she did this, cooked the rest of the meat and ate it that same day. She got food poisoning from the meat.
A couple of days later Nell noticed that Spot had not touched her offering.
The idea that animals have an in built wisdom that allows them to choose foods that are good, and also to choose foods that are medicinal when they are ill, is not based entirely on casual observation but is now a respected idea in zoology. Many studies are ongoing in the area of self medication by animals, and this subject has been christened with the imposing name zoopharmacognosy.
It has long been observed that many creatures have developed strategies for detoxifying their diets. Plants are eaten by animals. Plants are passive organisms in the sense that they cannot protect themselves by fight or flight.
However, many plants have evolved other means of protecting themselves, growing leaves laced with chemical compounds that have the properties of cardiac toxins, antifertility agents, hallucinogens and growth inhibitors.
Such chemicals are harmless to the plant but can be deadly to the animal that ingests them.
Many animals have developed counter strategies that enable them to eat the plants - they follow a poisonous meal by eating something that can detoxify the poison.
Rats display the best known example of this behaviour. They often eat clay after eating poisonous plants. The poison is absorbed by the clay. Similarly, cats and dogs are often seen to eat grass after consuming something that doesn't agree with them.
When given maximum flexibility to pick and mix their own diets, animals seem to make good choices.
In a classical experiment a balanced rat diet was divided up into 11 constituent parts. The rats were presented with 11 little trays each containing one component - protein, oil, fat, sugar, yeast, water, etc. The rats chose an efficient diet that allowed them to grow faster with fewer calories than rats fed the standard rat pellet diet.
Studies of monkeys in Tanzania have also revealed apparent self medication behaviour. On waking in the morning the monkeys dine on the leaves of the shrub Aspilia. They chew the leaves a little, then wad them and hold the wads under their tongues a while before swallowing.
The wads pass undigested through the digestive tract. The leaves apparently taste bad to the monkeys, as judged by the grimacing when the wads are held in the mouth.
Analysis of the leaves show they contain a chemical well known to be a strong toxin against fungi, bacteria and parasitic nematodes (round worms). It is estimated that in guts, without harming other useful bacteria.
Wadding the leaves under the tongue allows the active chemical to pass directly into the blood via the rich capillary bed located there.
In only one case of animals apparently showing self medicating behaviour has it been shown that the animal intentionally seeks out the antidote, having consumed the poison.
Rats eat clay to induce vomiting having been fed the poison lithium chloride. If they are conditioned to associate the taste of lithium chloride with saccharine they will eat clay after consuming saccharine, i.e., if a rat thinks it has eaten lithium chloride it wants to eat clay.
How do animals know what cures their ailments? It is tempting to think that animals are endowed with all sorts of innate wisdom, but this is a romantic notion and there is considerable evidence that much animal `wisdom' is learned behaviour.
Consider the following experiment. Rats were fed a diet that was deficient in the important vitamin thiamine. After a while the rats were given a choice the old thiamine free diet or a new thiamine rich diet. The rats choose the thiamine rich diet.
Animals are normally very cautious about eating a new diet. They usually only nibble at it, thereby lessening the chances of being seriously poisoned. However, in the thiamine experiment the rats on the thiamine free diet enthusiastically took to the thiamine rich diet when given a choice.
The explanation for the rats' behaviour is not that they sense that the thiamine rich diet is superior, but that anything is better than the thiamine poor diet they had been eating. This was checked by giving the rats on the thiamine free diet a choice between the old thiamine free diet and two new diets.
ONE of the new diets was rich in thiamine and the other was thiamine free. Half the rats chose the new thiamine rich diet and half chose the new thiamine free diet.
So, an animal eating a diet that makes it feel bad is very willing to drop that diet for an alternative diet. But how does an animal work out what new diet will make it feel better?
The workers who did the thiamine experiment with the rats made an important observation here. They noted that the social dimension was important. A rat is much more likely to choose a thiamine rich diet if it is surrounded by other rats who already prefer that diet.
There is one problem with the learned behaviour model. In learning theory, associations are made when cause and effect are closely linked in time. How could a monkey associate feeling better with a certain type of leaf it ate a week before?
One possible answer to this type of problem is that some animals have metabolisms that respond very quickly to the cure. These animals quickly learn how to cure themselves and confidently eat the new medicinal diet. The rest of the animals then mimic this behaviour.
In people, as with animals, social observation plays a critical role in determining what people eat and what medicines they take.
If you doubt this, consider for a moment what could be motivating so many people to eat those bland burgers from the fast food outlets. Or, what motivates so many people to try to drink thin cold beer through the narrow neck of a bottle. Or why so many people seek out antibiotics for ailments where antibiotics are ineffective.