Credited to Mali. A 2018 Current Biology study of 246 genomes placed domestication in the Inner Niger Delta in Mali. A 2019 PLOS Genetics study of 282 genomes argued instead for a non-centric, multiregional origin in which several parts of West and Central Africa contributed key domestication traits.
How it began
People grow two main rice species, African rice (Oryza glaberrima) and Asian rice (Oryza sativa), which were domesticated independently. An international study coordinated by IRD in France with CEA and the Africa Rice Center sequenced 246 African wild and cultivated rice genomes and identified the origin of African rice domestication as the Inner Niger Delta in northern Mali, more than 3,000 years ago. The researchers noted that this matches archaeological traces of rice domestication in the same area. The territory is in present-day Mali.
Before it existed
Before domestication, inhabitants of the Sahara harvested wild African rice. The genome study found that wild populations declined sharply, starting more than 10,000 years ago, as the Sahara dried. The researchers suggested that this depletion of wild resources may have triggered domestication, and that past climate change contributed to the emergence of African agricultural societies.
How it works
Domestication changed the wild plant through selection of useful traits. The genome analysis found convergent selection on a gene, PROG1, linked to an erect plant shape in both African and Asian rice, and a selection signature on a seed-shattering gene, SH5, in African rice only. Loss of shattering matters because grains that stay on the plant can be harvested rather than falling to the ground.
How it spread
According to the 2018 study, African rice cultivation expanded strongly about 2,000 years ago. During the last five centuries its cultivation declined sharply, a fall that coincided with the introduction of Asian rice in Africa. The two cultivated species had diverged genetically around one million years ago, well before either was domesticated.
Who pushed back
The single-origin account is contested. A 2019 study in PLOS Genetics analyzed 282 genomes of African rice and its wild progenitor and proposed that the crop was not domesticated in one central location. It argued that causal domestication mutations trace to wild progenitors in several locations in West and Central Africa, and that some supposed wild samples may be feral wild-domesticated hybrids.
