The South American highlands were a center of early agriculture. Genetic testing of the wide variety of cultivars and wild species suggests that the potato has a single origin in the area of southern Peru, from a species in the Solanum brevicaule complex. Over 99% of all modern cultivated potatoes worldwide are descendants of a subspecies indigenous to south-central Chile, Solanum tuberosum ssp. tuberosum, where it was cultivated as long as 10,000 years ago. According to George Raudzens, "It is clear that in pre-Columbian times some groups struggled to survive and often suffered food shortages and famines, while others enjoyed a varied and substantial diet." The persistent drought around 850 AD coincided with the collapse of Classic Maya civilization, and the famine of One Rabbit (AD 1454) was a major catastrophe in Mexico.