The biohistory of the human peopling of the Fuegian Archipelago and the processes of biocultural adaptation and microdifferentiation of the ethnohistorical ‘canoe’ (‘sea nomad’) and ‘foot’ natives are poorly known. Here we report the oldest human remains of a ‘sea nomad’ native discovered so far in the Beagle Channel region. The specimen consists of a deciduous molar from the site of Imiwaia I, dated to 5870 ± 145 years BP. The microwear pattern indicates the consumption of hard food processed by long chewing cycles. The histomorphometric analysis shows the presence of at least three episodes of stress between 8 and 10.5 months after birth, and an unusually thin neonatal line, suggesting a mechanically non-stressing birth event. Copyright © 2006 John Wiley & Sons, Ltd.