Baobabs and Humans:

Many of us have a special feeling about baobabs, those strange “upside down” trees with so many different links to humans. We might have been struck by their extraordinary shape while in Africa or the Kimberley. Perhaps we learned about the utility of these water-giving, food-giving, medicine-giving, fibre-giving trees and the ways that they can provide excellent material for rope, twine, cloth and boats. Or we might remember that delightful book for the young at heart, where “The Little Prince” is concerned that baobabs might take over his planet.

 Baz Luhrmann is crazy about baobabs. His recent movie “ Australia” has baobabs all over the place. Luhrmann’s artists even constructed a fibre-glass “boab”, as we Australians refer to our baobab. This creation features repeatedly in the movie, like an old-fashioned theatrical set. Remarkably, the artists who created this stage version of the boab gave it much longer stalks on the oval pods that hang from branches. This long-stalked trait has given rise to the “dead rat tree” moniker, one of the many nicknames for baobabs in Africa. In exaggerating the suggestion of dead rats hanging by their tails, the artists have inadvertently made a replica of the African baobab, which is pretty similar to the Australian baobab except for the long stalks on its flowers/pods. This is a case of art anticipating science, since recent molecular genetics has shown that the Australian and African baobabs are closer to each other than either is to any of the six species of baobab from Madagascar.

 The new data make it obvious that boabs came to the Kimberley from Africa . The data are not yet detailed enough to tell us when, nor to illuminate the means of transoceanic transport, which most people think was via floating seed pods. The floating pod hypothesis is not a strong candidate, despite its popularity. The Australian boab has pods with the thinnest shells of the eight baobab species, giving it the slimmest chance of making the journey before becoming waterlogged. Nor are the currents very favourable for such a journey, as they would more likely take floating seeds from NW Australia to Africa rather than the reverse direction. Finally, the distribution of boabs in the Kimberley is very narrow. If floating pods were a realistic option, one would expect boabs to have taken root at other locations in NW Australia, given that they tolerate a wide variety of difficult conditions and soil type. They should be common further down the Western Australian coast if transported by floating pods.

An alternative explanation for the transoceanic transport of boabs from Africa to Australia involves humans, who brought them deliberately to provide sustenance on the journey and the myriad uses on arrival. This would mean that boabs arrived in the Kimberley much more recently than is commonly believed. Despite this, there are presently no data that rule out a very recent arrival, and much more detailed molecular genetics would be needed to settle the question and to provide a date. The same techniques that have been used to elucidate the human migrations out of Africa can be used to study the origins of trees like the baobab, provided the appropriate, rapidly-mutating genes can be found in the mostly-conservative plant genome. Mitochondrial and Y-chromosome genes are now in agreement that a number of major human migrations took place out of Africa around 70,000 years ago. One cannot use mitochondrial and Y-chromosome genes  from plants, but a similar “haplotype analysis” is possible using different sets of DNA sequences from intergenic spacers that mutate more rapidly than the genes that they separate, which are very conservative in plants.

A large amount of painstaking work using molecular genetics will be necessary to test the idea that boabs are recent enough to be consistent with human transport to Australia. But there are a number of suggestive facts that support the investment required for such an investigation. First, the distribution of boabs in the Kimberley is identical to the distribution of Bradshaw paintings if one makes a little allowance for the spread of boabs from their original sites in the tens of millennia since their arrival. Bradshaw paintings are controversial  because of debate over their origins, but many unbiased observers are struck by the unusual inks (which penetrate the sandstone and are responsible for longevity that far surpasses ochre paintings), delicate techniques, provocative and mysterious content and extraordinary styles, that all suggest a distinct cultural entity with links to Africa. In the present context, Bradshaw art has frequent reference to boabs that suggest an intimate link that goes beyond what might be expected if the utility of boabs was discovered after the Bradshaw culture arrived in the Kimberley. Finally, Bradshaw art depicts large ocean-going boats that could accommodate as many as 30 passengers, the depictions suggesting  the “bundle of fibres” mode of construction used by Thor Heyerdahl in “Kon Tiki” and “Ra”, but which may have been boab fibres rather than reeds. The pods of boabs are convenient packages containing edible, nutritious seeds, and pulp that is refreshing and loaded with Vitamin C. The pods keep for over a year and would recommend themselves for a long sea journey in a way that no other Palaeolithic food could have compared. Moreover, there are so many different uses to which boabs can be put for water, food, medicine and workshop, that seeds or even seedlings/cuttings would be high on the list of priorities for the cargo of any trans-Indian Ocean expedition.

The central role played by baobabs in an ancient culture before the development of agriculture can be gleaned by study of the Hadzabe in NW Tanzania. The Hadza language uses clicks, like the Khoisan, and phylogenetic analysis suggests that Hadza and Khoisan are the two oldest languages on the planet, both going back more than 40,000 years without showing any signs of their joining. The Hadza hunter-gatherer existence gets most of its calories from plant food, with less than 20% derived from hunting. The great majority of their plant-derived food comes from the baobab, particularly the seeds, which are tasty and high in protein and fat.

Baobab seed pods hang on the tree during a large part of the year, an unrecognised insurance against catastrophe in the days before harvests, granaries and prescient Josephs. In fact, one might argue that the baobab actually insured against the obliteration of the whole human race, since it is hard to imagine any other factor that would have so effectively mitigated against the biggest catastrophe ever to have hit humankind:- the Toba event.

Toba was a supervolcano, 74,000 years ago, that has dwarfed any other eruption in the last 2 million years. A kill zone of metres-deep ash can be defined North of the equator from the eruption site in Sumatra, westward (because of the earth’s rotation) over India, the middle-East and Africa. Darkness and cold would have afflicted the whole globe for around 1 year and climatic disturbance would have followed for decades. The small chances of survival after the Toba event have been linked to the genetic bottleneck that humans squeezed through ~70,000 years ago. The tiny amount of genetic variability in present day humans, despite our large population, has led to calculations of the size of the founding population after the bottleneck. Although it is no longer thought that there was only a single female ancestor, Mitochondrial Eve, the estimates are still very small, around 100-1000 human survivors in toto.

How would a hunter-gatherer survive a cold, dark night that lasted a year? Even if animal prey managed to survive somehow in the dark and cold when the plants died out, catching them in the dark would be fiendishly difficult, perhaps with snares. Chances of collecting enough food might be better on the seashore, where shellfish could be gathered by feel. This would obviously be easier for an established seafood culture that had developed habitual haunts and techniques. It would be far more difficult in a temporary attempt to access the shellfish niche. Back at a forest camp with a group like the Hadza, survival chances would be enhanced by their knowledge of the locations of baobabs in their area, which could be found in the dark and harvested using the familiar topology of these trees (in contrast to the need to learn new topology if a coastal niche were being exploited for the first time). The Hadzabe presently show great skill in climbing baobabs to rob beehives of honey and wax, so retrieving pods in the dark would not be expected to present great difficulties for ancestors if we assume that they had a good memory for the location of baobabs in their area. A hooked pole and a flaming torch would also have helped to retrieve pods.

The extraordinary resilience of the deciduous baobab (whose mature tree can resist fire, and regenerate all of its bark if it is removed) and its readiness to become dormant in drought or dry season, would all give it a much better chance of surviving the catastrophic cold and dark of the Toba event. The Achilles heel of the baobab is frost, but one can calculate that Tanzania, just south of the equator, would not have been cooled to zero as a result of the Toba event, which is calculated to have produced a 12 C deg drop worldwide. More important than the tree’s resilience perhaps, is the ~ 1 year longevity of pods. Depending on the exact timing of the Toba event, the extended availability of pods might have ensured a supply of food that was obtainable in the dark and that made the difference between life and death. In these terms, the baobab might be responsible for the survival of humans on the planet!

If this is true, one would expect that the surviving culture, saved by baobabs, would recognise this fact. Accordingly, their culture might develop a level of spiritual reverence and ceremonial significance for the baobab, hints of which seem to be found in parts of Africa today and in Bradshaw art. The fundamental importance of baobabs is also reflected in the fact that a large number of African languages have similar or identical words for tree and baobab, while the words for other kinds of tree are dissimilar.

The steady improvement of physical and molecular biological methods for approaching these question improve one’s chances of illuminating the possible intimate connection between humans and baobabs