Helminths and human ancestral immune ecology: What is the evidence for high helminth loads among foragers?

OBJECTIVES

Recent theories of human immune ecology have invoked high helminth loads as an important selection factor among early humans. However, few studies have assessed this assumption among extant human foragers.

METHODS

We review the current evidence for high helminth loads in documented forager populations and present new data from members of a Kawymeno Waorani forager group in Amazonian Ecuador (n = 16) compared with neighboring Kichwa subsistence farmers (n = 63).

RESULTS

Stool samples indicated a near absence of helminths among the Kawymeno foraging group (6.25% with Ascaris lumbricoides and 0% with Ancylostoma duodenale or Trichuris trichiura). In contrast neighboring, isolated Kichwa subsistence farmers in a similar ecosystem had abundant helminth infestations (76.1% with Ascaris lumbricoides, 11.1% with Ancylostoma duodenale, and 1.5% with Trichuris trichiura). The presence of helminths among the Waorani and Kichwa was triangulated across multiple data sources, including presence in stool samples, medical exams, and 3 years of participant observation.

CONCLUSIONS

These findings, coupled with the modern forager literature, raise questions as to whether helminths were prevalent enough in Paleolithic humans to be a unique evolutionary selective force in human physiology.