Scientists have uncovered the origins of the coffee plants responsible for the majority of the world’s coffee supply, tracing their emergence to a hybridization event that occurred around 600,000 to 1 million years ago in the forests of Ethiopia. Through population genomic modeling methods, researchers determined that the original Coffea arabica plants developed as a result of natural hybridization between two other coffee species, Coffea canephora and Coffea eugenioides. This hybridization resulted in a polyploid genome, meaning each offspring contained two sets of chromosomes from each parent. This may have provided a survival advantage, enabling Coffea arabica to thrive and adapt to various conditions.
The researchers used genetic information from 41 samples of Coffea arabica from diverse locations, including an 18th-century specimen. Despite a margin of error in the estimated time of hybridization, the study suggests that this event occurred during the Pleistocene epoch. The hybrid genome enabled the plant to flourish as it was cultivated across the world, with its origins believed to be in Ethiopia, from where it spread to the Middle East and beyond.
However, the polyploid nature of Coffea arabica’s genome also left it vulnerable to disease, particularly coffee leaf rust (Hemileia vastatrix). Genetic bottlenecks due to climate variations and human cultivation further reduced genetic diversity. The fact that all current Coffea arabica plants can be traced back to a single parent has created an additional bottleneck, limiting its ability to confront rust in an ‘arms race’ with evolving rust populations.
In 1927, Coffea arabica naturally crossed back to one of its parent species, Coffea canephora, on the island of Timor. This event created a more rust-resistant variety of coffee, but the quality of the beans was inferior to those produced by Coffea arabica or Robusta (another name for Coffea canephora). Nevertheless, the discovery of the hybridization event that led to the emergence of Coffea arabica provides valuable insights into the origins of this globally consumed beverage, highlighting the role of natural cross-pollination and polyploidy in plant evolution.
