In our paper just published in PLOS ONE, we show that humans were the main agents for dispersing the boab (Adansonia gregorii) in the Kimberley region of northwest Australia. We combined evidence from boab genetics and linguistic word-forms for boabs in the Aboriginal languages of the Kimberley with palaeoclimatic and archaeological studies, to reveal that these ancient settlers in the remote northwest were responsible for bringing the boabs inland as sea levels started rising dramatically 20,000 years ago.
The results of our study reveal the mystery of ancient Aboriginal settlement and interaction in the Kimberley. Aboriginal peoples probably lived along the northwest coastal areas of the exposed continental shelf during the last Ice Age and retreated inland as these areas were flooded by rising sea levels. They carried boab fruit with them as they moved inland into central and eastern parts of the Kimberley region, and introduced the tree and associated words to other Aboriginal communities living there.
We wouldn’t have stumbled upon this discovery if we hadn’t been trying to solve another mystery about how the boabs got to Australia and why their geographical distribution is limited to the Kimberley region. The prevailing theory is that the ancestor of the boab came in a fruit pod that floated across the Indian Ocean from Africa or Madagascar and made landfall somewhere on the northwest coast. Once there, it evolved into a different species over several million years and gradually assumed its natural distribution through seed dispersal by animals and floods.
This theory raised more questions than answers for us. If the boab had been in Australia since it diverged from its sisters in Africa and Madagascar, surely there would be more than one boab species? The reasons for why there was just a single boab species could be either because the ancestor arrived fairly recently in Australia and didn’t have enough time to speciate, or that there was a lot of gene flow happening between boabs. The Kimberley has a number of biogeographical barriers which have influenced speciation in rock wallabies, geckos and bloodwoods. So, for there to be significant gene flow among boabs across the Kimberley, there had to be some agent that could carry the seed over long distances and across these barriers. And the result was….?
Read the paper to find out whodunit, and how it helped us solve the mystery of ancient human settlement in northwest Australia.