Why are Polynesians much larger than most? Ancestral sea trips offer strong link

While much of East Polynesia has a tropical climate, the southern third, including New Zealand, experiences a warm-to-cool temperate climate. This climatic variation might explain why New Zealand was one of the last habitable places on Earth to be settled. The first settlers arrived in New Zealand around the 14th century.

To evaluate how body size influenced energy expenditure for thermoregulation (maintaining body temperature) during the voyages, the researchers considered three body types: one resembling modern Polynesians, a second with higher weight, and a third with higher body weight and additional subcutaneous fat layer thickness.

Using a voyage simulation model that estimates daily distances based on winds and currents, combined with likely environmental conditions, such as air temperatures and wind, the energy required to maintain body temperature during the journey from Tahiti to New Zealand was calculated.

They compared this to the energy requirements for a similar trip to Hawaii (approximately 23 days).

The study's results revealed that for a summer trip (which would require less energy than a winter trip), each traveler bound for New Zealand would need an average of an extra 965 calories per day to maintain their body temperature, compared to those traveling to Hawaii.

If the additional energy requirement were entirely met by burning fat, those sailing to New Zealand would lose an average of 5.9 extra pounds throughout the 25-day journey. 

If the difference were compensated solely by muscle mass, the overall weight loss would be around 13.3 pounds.

Ultimately, the model calculations indicated that individuals with larger body sizes experienced lower heat loss, giving them an energy advantage over those with smaller body sizes. This advantage was more pronounced for females.

These findings align with the larger body sizes observed in present-day Polynesian populations, with females being approximately 31 percent heavier and males 24 percent heavier than populations to the west of Polynesia.

"Our analysis can't definitively prove that the size differences we see in Polynesia today are the result of larger people being more likely to survive the original trips and colonizing the region, but it certainly is consistent with that fact," Montenegro concluded.

The complete study was published in PLoS ONE and can be found here.