How did the first arabica coffee tree originate?

Nowadays, approximately 60-70 per cent of global coffee turnover is Arabica.

The experts examined more than 30 different plants of this variety, including an 18th century specimen from the Natural History Museum in London.
The population of this variety of coffee had been changing for thousands of years before humans began to cultivate it. The population bottlenecks were caused by bad harvests, with only a small fraction of plants surviving.