Bridal gifts and caterpillar gods

As you may be aware, Ecowarwicker sits within our broader research group and our broader conservation interests. One of those is our interest in the conservation genetics of crops. This last week we published in Science some fascinating work on cassava in collaboration with the Smithsonian Institute and Embrapa. Cassava is grown throughout the tropics, mostly by vegetative propagation. We were super surprised to find the crop has retained ALL its genetic diversity. How?

Dibber tool used to plant cassava adorned with the Kukurro caterpillar god

Well, from our work with the indigenous tribes of the Xingu in Brazil we learned how cultural practices over the past 4000 years or so are responsible. Although vegetatively propagated, occasionally new cassava varieties appear from sexual crosses by accident - 'cassava from the sky'. These varieties are tested by the tribes, and if they like them, they keep them. But here's where the religious culture plays an important role. The catapillar god Kukurro is the deity associated with cassava. When the crop is planted a 'Kukurro house' is built as an offering to the god, which is a mound of earth with a crown of cassava sticks protruding of different varieties. It is a quirk of clonal lines that to get successful crosses you need to cross quite distantly related individuals. The Kukurro house causes this to happen. This way the religous practices of the tribe repair the genetic diversity of the crop. Then, when the time comes to marry, brides will take the households varieties with them to new tribed, so spreading new varieties right across the continent in the end. We found highly closely related plants from thousands of miles apart. Outside of this homeland no new varieties are produced because cassava is just clonally propagated, and subject to the gradual genomic decline that goes with that. Here we see how indigenous cultural practices on the small scale are so important to global food security.