People and the dispersal of baobabs around the Indian Ocean

[reposted from christiankull.net]

The baobab, that iconic, majestic, and grotesquely massive roots-in-the-sky tree, teaches us something surprising about “nature”.  It demonstrates that what appears to be “natural” has been – for millennia and millennia – also fundamentally “social”, for people have been important dispersal agents of these trees.  Researchers like Chris Duvall and Jean-Michel Leong Pock Tsy have shown this for the African baobabs.[1,2]  Our recently completed research project, led by Priya Rangan, demonstrates this in multiple ways around the Indian Ocean.  Baobabs are such useful and remarkable trees [3], it is hardly difficult to imagine people not picking up the hard but pleasantly light and fuzzy fruit pods and walking with them.

A young baobab near an Aboriginal rock art site

A young baobab near an Aboriginal rock art site (photo: CKull)

One part of our project looked at the single species of baobabs found in Australia: Adansonia gregorii, called boab. It grows in the Kimberley region in the northwestern part of the continent.  In a study just published in PLoS ONE [4], we combine evidence from baobab genetics [5] and Australian Aboriginal languages to show that humans have been the primary agents of baobab dispersal.  In particular, we reveal their crucial role in dispersing baobabs inland from now-submerged areas of northwest Australia during the dramatic sea-level rises at the end of the last glaciation.  (See also Priya’s blog about the study)

A further question is how the baobabs arrived in Australia in the first place.  Oceanic dispersal via seed pods floating in currents, several million years ago, remains the most plausible explanation, as our collaborator David Baum has shown [6].  Yet, another one of our baobab collaborators (and veritable Renaissance man) Jack Pettigrew advances an interesting speculative argument about a possible human role in transporting the baobabs, building on evidence from rock art in the Kimberley and in Tanzania [7].  Karen Bell, who worked as a post-doc on our project, in 2012 helped Jack demonstrate that upland baobabs in eastern and southern Africa were actually a different species from the pan-African baobab Adansonia digitata.  They named it Adansonia kilima [8].

Another part of our project investigates the dispersal of African baobabs to other parts of the Indian Ocean.  Adansonia digitata grows (or grew) in diverse places around peninsular Arabia, coastal Iran, Pakistan, India and Sri Lanka [3], as well as near old settlement sites on the northwest coast of Madagascar (a country with its own six species of baobab).  It is often stated that “Arab traders” brought baobabs to these places.  Yet this incomplete and misleading, as Priya and Karen show in their study of baobabs in India [9, 10], where the tree is found in several widely dispersed regions. They piece together evidence from molecular genetics of baobab trees, ethnographic observations of rituals and language, and archival and historical sources.  They confirm that baobabs have indeed been introduced to India, but that the introductions are multiple, from different sources in Africa, and possibly quite ancient (several 1000s of years), and likely involved African sailors, migrants, merchants, soldiers, and slaves.

More “recent” networks of exchange continue to move baobabs from place to place.  European colonialism led to the introduction of the tree to other Indian Ocean islands, like Reunion and Mauritius, and places further afield like Malaysia or the Caribbean.

This research was funded by an ARC research grant called “The Enigma of Arrival”.

References cited

[1] Duvall, CS (2007) Human settlement and baobab distribution in south-western Mali. Journal of Biogeography 34 (11):1947-1961.

[2] Leong Pock Tsy, J-M, R Lumaret, D Mayne, AOM Vall, YIM Abutaba, M Sagna, SOR Raoseta & P Danthu (2009) Chloroplast DNA phylogeography suggests a West African centre of origin for the baobab, Adansonia digitata L. (Bombacoideae, Malvaceae). Molecular Ecology 18:1707-15.

[3] Wickens, GE & P Lowe (2008) The Baobabs: Pachycauls of Africa, Madagascar and Australia. Springer.

[4] Rangan, H, KL Bell, DA Baum, R Fowler, P McConvell, T Saunders, S Spronck, CA Kull & DJ Murphy (2015) New genetic and linguistic analyses show ancient human influence on baobab evolution and distribution in Australia. PLoS ONE 10 (4):e0119758. pdf

[5] Bell, KL, H Rangan, R Fowler, CA Kull, JD Pettigrew, CE Vickers & DJ Murphy (2014) Genetic diversity and biogeography of the boab Adansonia gregorii (Malvaceae: Bombacoideae). Australian Journal of Botany 62 (2):164-174.

[6] Baum, DA, RL Small & JF Wendel (1998) Biogeography and floral evolution of baobabs (Adansonia, Bombacaceae) as inferred from multiple data sets. Systematic Biology 47 (2):181-207. pdf

[7] Pettigrew, J (2011) Iconography in Bradshaw rock art: breaking the circularity. Clinical and Experimental Optometry 94 (5):403-417.

[8] Pettigrew, JD, KL Bell, A Bhagwandin, E Grinan, N Jillani, J Meyer, E Wabuyele & CE Vickers (2012) Morphology, ploidy and molecular phylogenetics reveal a new diploid species from Africa in the baobab genus Adansonia (Malvaceae: Bombacoideae). Taxon 61 (6):1240-1250. pdf

[9] Rangan, H & KL Bell (2015) Elusive traces: baobabs and the African diaspora in South Asia. Environment and History 21 (1):103-133.

[10] Bell KL, H Rangan, CA Kull, and DJ Murphy (n.d.).  This paper on the history of Adansonia digitata introduction to India using molecular genetics is currently “in revision”.  I’ll update this link once it is published.

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