Lewis Honors College Capstone Collection

Year of Publication



Arts and Sciences



Degree Name

Bachelor of Science, Biology

First Capstone/Thesis Advisor

Dr. Carol Basin


Cycads are a group of ancient gymnosperms with a rich fossil history. While they once dominated the world’s forests, their adaptation to warm climates has now restricted them to tropical areas. They are not widely eaten by humans due to their known toxicity, but some indigenous groups of the Pacific Islands, such as the Chamorro people of Guam, have developed methods of washing the seeds for safe consumption. Cycad seeds are a common dietary item of several mammals. One such mammal, the flying fox, is considered a delicacy to several indigenous groups. In the mid-twentieth century, these groups also expressed an extraordinarily high rate of a rare and severe neurodegenerative disease known as the amyotrophic lateral sclerosis-parkinsonism dementia complex, or ALS-PDC. An early hypothesis for this high rate of ALS-PDC was toxicity resulting from the widespread consumption of cycad seeds. This was later rejected due to the finding that the washing techniques removed a sufficient amount of toxins to eliminate the possibility of negative effects. The cycad hypothesis was revived when it was discovered that large quantities of cycad toxins accumulate in the tissues of mammals such as flying foxes. Consuming even a single flying fox would deliver a similar amount of cycad toxins as up to a thousand kilograms of cycad flour. Given the demonstrated neurotoxic effects of several cycad toxins, as well as the correlating decline in rates of ALS-PDC and flying fox consumption, it is likely that an underlying cause of ALS-PDC is consumption of flying fox tissues containing bioaccumulated cycad toxins.

Included in

Biology Commons