Fishing for iodine: what aquatic foraging by bonobos tells us about human evolution

Abstract

BackgroundExpansion of brain tissue and development of advanced cognitive skills are characteristic traits of human evolution. Their emergence has been causally linked to the intake of nutrients that promote brain development and iodine is considered a critical resource. Rich sources of iodine exist in coastal areas and evolutionary scenarios associate the progressive development of brain size and cognitive skills to such landscapes. This raises the question of how early hominins living in continental areas could have met their iodine requirements. One way to explore this question is to use information from hominoid primates as a proxy for the nutritional ecology of early hominins. Bonobos are particularly interesting in this context as they are restricted to the central part of the Congo basin, an area considered to be iodine deficient based on human standards.MethodsPooled samples of fruit, terrestrial and aquatic herbs were used to assess mineral content with an inductively coupled plasma optical emission spectrometer. Iodine content was measured with the catalytic technique of Sandell-Kolthoff and two separate inductively coupled plasma mass spectrometry methods.ResultsNutritional analyses revealed that the mineral content of aquatic herbs is higher than in other plant foods. Moreover, two species of aquatic herbs consumed by bonobos contain iodine concentrations that are almost equivalent to marine algae.ConclusionsThese data challenge the general notion that the Congo basin is iodine deficient and demonstrate that its lowland forest offers natural sources of iodine in concentrations high enough to prevent iodine deficiency in hominoids and humans.