Versamelde werke

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2 Habits Acquired in Different Environments

An outstanding characteristic of the chacmas is their ability to thrive in the most varied environments. They are equally at home on the fertile mountains of the Cape and in the sterile hills of our more northerly terrain. In the Cape they are in the midst of a plentiful and varying food supply. Here, as Darwin has pointed out, the proportion of different species of plants to the extent of soil area covered is greater than in any other continent, and no less plentiful and varied is the insect-life. The mountain-masses of the Cape afford, therefore, a safe retreat in the midst of thickly populated districts, and their protective value is chiefly due to the fact that natural fertility renders it unnecessary for the baboons to engage in the dangerous expedient of exacting contributions from the farms of their human neighbours.

It is hard to imagine an environment more different from this land of plenty, with regular rains, sheltering caves, precipices and forests and perennial mountain streams, than the rugged, sterile hills of the north, where existence has become an unending struggle for the chacma. Not only is his life more instantly jeopardised on these low and shelterless hills by the presence of man, but the question of a sufficient food supply has become a complex problem. Yet even here the chacma thrives under conditions which would, I should imagine, have brought about the extermination of any other species of gregarious mammal. Indeed, many great species of mammalia have been exterminated in this country under conditions far more naturally favourable.

But there is an even more profound difference in natural environment than the one created by difference of locality only. It is beyond doubt that the great majority of the species have only in recent times ceased to be arboreal animals and have migrated to the hills and mountains under pressure of defensive necessity and have become purely mountain animals.

There are instances where such migrations have taken place within the memory of man. But this change in natural habitat has not been universal. Along the great river-ways of South Africa in the less populated regions, there are still great numbers of baboons inhabiting the forests, where they live as largely arboreal animals.

It will be realised how very different their habits and general way of life must be to render existence possible under two such radically different sets of natural conditions. The ‘tree’ or ‘river’ baboon is popularly spoken of as a distinct variety or species, a designation which has no other foundation than these greatly divergent habits. These different habits are not determined only by the difference in the natural food supply or by the difference in environmental dangers; they are brought about by conditions which affect the entire exist-

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ence of the animal in its relation to nature. They differ no less profoundly in some of their habits than, for instance, the klipspringer (Oreotragus saltator) and the steenbok (Neotraginus). None the less, they are the same species, and there is no morphological reason for describing the river baboon as a ‘local variety’ in the generally understood sense. Nor is there any hereditary limitation to one environment, as there would be in all lower animals similarly placed. We established experimentally that if an infant arboreal baboon is given to a mountain troop, it is adopted and grows up with the complete knowledge necessary for it to exist in its new environment.³

Among the higher vertebrates the nature of their food supply is certainly a great element in determining the course of psychic and morphological specialisation: the aardvark (Orycteropus afer afer) - an animate digging machine, toothless, with its long sticky tongue, its wonderful instinct for locating deep termite nests in hard soil; the remarkable bodily structure of the giraffe; the conversion of the flying wings of the penguin into paddles - all were modifications selected primarily by the adoption of a special food supply, and this is the case in most higher animals. It seems also to be a general rule in nature that any sudden change of environment involving the loss of natural food supply - although food for which the organism has not been specialised may be plentiful in the new environment - means destruction.

For instance, the South African otter can, in captivity, subsist on warmblooded terrestrial animals exclusively, without ever entering water, and yet several instances came to our notice where otters were driven by drought to take up their residence at shallow inland pools without fish or crabs, and they invariably died of hunger, although small terrestrial animals abounded in these drinking places. It is hardly conceivable that structural modification in this case rendered the capture of sufficient animals to sustain life impossible. It was ‘instinct’ that stood in the way.

This example emphasises the fact that the psychic specialisation is generally more powerful in confirming an animal's reaction to a definite environment than correlated somatic modifications. It is true that species outside the order of primates have been known to adopt new habits because of a radical change of food, but all the instances I know of clearly resulted from certain definite influences that are not present in the chacma.

In this country the rhinoceros-bird, which used to relieve the now vanished thick-skinned game of ticks, has undertaken the same office for the thinnerskinned domestic animals. The removal of a tick from cattle frequently leaves a small open wound, and in such cases the bird eats the exposed flesh, often causing severe, if not fatal, injuries. From this habit it was an easy transition to the practise of attacking any open wounds on cattle. The Australian parrot which has taken to picking holes in the backs of sheep is similar. It is said the habit

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originated in a resemblance between the wool of the sheep and the covering of a fruit commonly eaten by the bird.

In these few instances, one principle invariably underlies the change of habit: the suggestive influence on the hereditary instinct directly conveyed by a natural food. In the chacma no such connection can be traced in the majority of new food-habits.

The natural food of the chacma consists of fruits and insects. I know of no verified instance where, under natural conditions, the flesh of warm-blooded animals is habitually eaten.⁴ Now if any two extremes of locality inhabited by the chacma are considered, it will be found that the species of insects and fruits which constitute their principal food supply vary greatly and, although the nature of the supply is identical, the means of utilising it differ more profoundly than in any other lower animals, however widely dispersed. But, in addition to these varying methods of procuring natural food, what may be described as supplementary habits have been acquired in different localities which are altogether outside the order of nature - as one conceives that order to exist in case of the higher mammalia - habits which at once place the chacma in a class by itself. It is necessary to refer to only a few of these personally verified habits in order to convey an idea of the singularity of the animal in this respect:

The southern limit of the baobab tree (Adansonia digitata) is the far north of the Transvaal, where it grows to a great height and size, dominating the entire forest. It bears a fruit containing a sub-acid pulp popularly valued as a febrifuge and for making cooling drinks. This fruit is doubly protected, for it grows at such great height from the ground that until it drops, only birds and arboreal animals can reach it, and its outer shell is so hard that it resists all attacks. I know of no animal that under natural conditions can reach the edible core or habitually use the fruit as food. The chacma was the one exception.

A troop we had an opportunity of observing travelled great distances to reach the isolated baobabs that are scattered through the Bushveld. The country between the trees and the group of hills they inhabited was generally sandy and stoneless. They would pick the fruit and carry it for great distances to the foot of the hills, where the nearest stones were situated. The fruit is about the size of a small coconut, and the means the chacma adopted for carrying it to the hills was very interesting. The adults generally carried four: one held in the teeth by the stalk on which it grew, one under the right arm, and one in each hand, the animal treading on those held in the hands. We never saw fruit carried under the left arm. On reaching the hills, the fruit was placed on a flat rock and smashed with stones. My colleague noticed that in many instances, particularly among the younger individuals, great efforts were first made to break the fruit by hammering it on the rock by hand before a stone was used as a tool. Often all efforts would fail to break the fruit. It was then rolled off the rock and

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never touched again. In no other locality we visited where these trees grew did we come across this habit.

This group in the Magalakwên Valley had also acquired a habit which evinced just as high a conception of means to a definite end. They inhabited an isolated precipitous group of hills about five miles from the river. At the time we came in contact with them a prolonged drought had dried up all the springs and drinking places in the hills, and the nearest water they could reach was in the river bed; even here the only means of reaching it was by digging deep holes in the shifting sand. To get to the river bed they had to traverse a very exposed tract of country and cross a big road, the sort of journey to which the chacma is decidedly averse.

Very often the presence of human beings in the vicinity meant the baboons had to go without water for several days, or jeopardise their lives in reaching it. But we found the hill-sides strewn with the chewed fibres of a bulb which proved to be that of a lily which contains a great deal of moisture. The bulb grows at a considerable depth, generally under stones or in soil which in drought is almost as hard as stone. A long rush-like leafless stalk grows out of the bulb and, after a number of twistings underneath and past stones, reaches the surface. A slight pull at this stalk detaches it from the bulb or breaks it deep down, and once it is detached it is almost impossible to find the bulb by digging. Not only had the troop of chacmas discovered that this bulb would assuage thirst, but their method of reaching it showed that they fully appreciated the chief defensive attribute of the plant, and used the only means for overcoming it. In digging they were careful not to detach the stalk, but dug down round it, removing the stones, and so tracing it to the bulb. We never saw this bulb dug up or chewed anywhere else. In the vicinity of our own troop which we kept under continual observation, the plant was plentiful but it was never used by the baboons.

No less remarkable is the habit which has gained for the chacma a notoriety which was perhaps the chief reason that induced the Government to place a price upon its head. The animal is no flesh eater and no bird or mammal is ever killed for food, yet throughout the sheep districts of the Cape a great many young lambs are killed by baboons. The flesh is not eaten; their only object is to secure the curdled milk from the stomach. Here in the northern Transvaal the habit has not been acquired. No lamb is ever touched although a troop may be in contact with flocks of sheep almost daily.

Another troop which we had an opportunity of watching for a day had discovered a similarly ‘rational’ method of overcoming an environmental difficulty. The presence of man in their neighbourhood had left them only one drinking place that could be visited with any degree of safety. This was a thermal spring. The water in the spring itself and for some distance downstream

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was too hot to drink, and a farmhouse, towards which the water flowed, made it dangerous for the baboons to go farther downstream. But whenever they were satisfied that danger from the farm was not too threatening they visited a spot where the water was drinkably cool. Very often this was impossible for long periods, as the farm-lands extended right up to this place and men were working in the vicinity. The baboons were then compelled to find water in the spring itself or immediately below it. On the occasion we observed their behaviour about a third of the troop lined up along the water course below the spring and each one scooped a furrow through the mud. When these furrows were filled with water they moved farther up the hill-side to wait for it to cool.

The larger portion of the troop, agitated and uneasy, did not approach the water at all while these operations were going on. They awaited the results of their friends' labours at a safe distance. Those that took part in the operation of making the furrows consisted of about equal numbers of adults and young ones, and the difference in their respective behaviour was interesting. The adults went about the work quietly, methodically and phlegmatically, after the chacma manner, but the youngsters were greatly excited, jerking out the mud erratically, and frequently, when the hot water came in contact with their hands, uttering cries of rage.

After about an hour's wait on the hill-side, the whole troop again approached the water and commenced drinking out of the furrows. We noticed that only a very small percentage of these were used and each baboon quietly waited his turn to drink. The reason became apparent on closer examination. The mud was generally so soft that many furrows were soon obliterated and only those dug in the firmer area lasted long enough to cool the water. But even the majority of these could not be used because they were made the wrong way. Whenever the furrow was dragged in a more or less downstream direction, the continual entrance of hot water prevented cooling. A small proportion were scooped out more or less upstream or at right angles to the current and in these the water cooled more quickly. Whether the correct method was adopted by accident or design it was impossible for us to establish, since we had no opportunity of ascertaining whether the same individuals always adopted the same method of construction.

It needs no wide systematic knowledge of animal behaviour to recognise the great difference there is between habits such as these and the greatest adaptability conceivable in animals below the primates. No other animal, under any circumstances, would or could behave in exactly this way, although it might prove difficult to define in other than general and unmeaningful terms the real nature of the difference. And without an appreciation of the significance of these peculiarities it will be found difficult to form a satisfactory conception of the chacma's place in the scheme of mental evolution.