Decolonizing the “Thrifty Genotype” Hypothesis
The following article was penned by our guest writers from the School of Biomedical Sciences, University of Otago, New Zealand: Dr. Anna Gosling, a Research Fellow in the Department of Anatomy, and Dr. Tony Merriman, a Research Professor in the Department of Biochemistry:
Like the ocean that laps on the shores of the islands throughout the Pacific, it comes in waves. Every few years, the oft-repeated “Thrifty Genotype” Hypothesis, first put forth by James V. Neel back in 1962,¹ is invoked to explain the high burden of obesity, type 2 diabetes and other metabolic conditions in Pacific communities (and in fact, many other Indigenous peoples).
The fundamental basis of the hypothesis is alluring in its simplicity — that genetic variants or “genes” which promoted efficient fat deposition or superior energy usage would have been advantageous because they allowed those who possessed them to survive periods of famine during our evolutionary past. In modern conditions of relative abundance, these genes would be disadvantageous because they promote fat deposition and insulin resistance in preparation of a famine that never comes. It is a seemingly simple and elegant explanation — but one which falls to pieces when one considers the implications too closely, for populations worldwide more generally, and particularly when one considers more closely the evolutionary history of the Pacific and recent history of colonialism.
Understanding the evolutionary history of the Pacific region and the colonization process is essential when applying an evolutionary hypothesis such as the “Thrifty Genotype” hypothesis. It is a region with a deep history, where some of both the earliest and the most recent population settlements occurred — with the arrival of people in Australia and Papua New Guinea around 50,000 years ago (onto the ancient continent of Sahul), more recent expansions of Austronesian-language speaking peoples (associated with the Lapita culture) around 3,300 years ago (as far as Tonga and Samoa), and then finally the settlement of the eastern Polynesian Islands (eg. Hawai’i, Cook Islands, Rapa Nui, Aotearoa New Zealand) between 800 and 1,000 years ago.² While we don’t have much evidence surrounding the rapidity of the earliest migration, we do know that the latter two occurred extremely fast, over the course of only a few hundred years.³
In the context of the Pacific, we assert that the “Thrifty Genotype” hypothesis relies on significant population loss mediated by restricted food supply, possibly operating in two different ways: a) starvation during the voyaging and settlement of the Pacific, or b) Pacific Island populations might be subject to more famine events because of their relative isolation and their susceptibility to cyclonic weather patterns and tsunami.
Scenario A assumes that the voyaging process was perilous with a high mortality rate. However the process of colonizing the Pacific is likely to have involved safe, systematic, and planned exploration prior to the colonization. The speed at which successful settlement of the wider Pacific region occurred could not be sustained if there was great loss of life. During the 1950s and 1960s, there were debates about the deliberate nature of Pacific voyaging and navigation, with theorists such as Andrew Sharp arguing for “accidental voyaging.”⁴ However most scholars now agree that preliminary scouts were sent out on two-way exploratory voyages prior to the departure of a well-provisioned and well-informed colonization party traveling to a known destination. Weather patterns such as El Niño may also have contributed to easier sailing during certain periods, making voyaging times faster.⁵,⁶,⁷,⁸
Starving at sea is not the only voyaging-related proposal put forth to explain genetic diversity in the Pacific. A few theorists such as Phil Houghton have suggested that the increased body mass among Aotearoa New Zealand Māori and other Polynesian populations is a result of selection due to the cold temperatures faced during open ocean voyaging, the premise being that higher body mass would insulate one against wind chill and ocean spray (an adaption of a hypothesis known as Bergmann’s rule).⁹ While Houghton performed some sophisticated calculations to show the likelihood of survival for 10 days voyaging on open ocean at various latitudes, these calculations assumed naked bodies that have no cold protection. This does not fit with knowledge of Polynesian voyaging and there is historical evidence for protective clothing and structures in the canoe allowing for some weather protection.¹⁰,¹¹
Scenario B, where Pacific populations suffered periods of famine because of their apparently fragile island environments which are vulnerable to phenomena like tsunami and cyclones, is also overly simplistic. It does not appreciate the variation in subsistence patterns seen across the Pacific, which is partly a result of the different geological origins of inhabited islands, such as atolls vs volcanic islands vs continental islands. Water availability and soil composition will affect what horticultural domesticates can grow, whether a sizable surplus can be produced, and even the sorts of endemic flora and fauna that can be utilized. Different islands are likely to have had quite different levels of vulnerability when faced with natural disasters. The distribution of obesity- and metabolic disease- prone populations through the Pacific, under this model, would require multiple independent episodes of selection for a “Thrifty Genotype,” which would mean that we’d expect to see a different genetic contribution to phenotype in each population.
Finally, we need to consider what sorts of populations this hypothesis is being applied to. Why is it that when the suggestion of “thrifty genes” comes up, often European populations are not considered? In reality, almost every population in the world is likely to have suffered from periods of reduced food supply at some relatively recent point — so we should probably all have thrifty genes. We know that during the Little Ice Age, a period between 1300 and 1870, European and North American populations were subject to much colder winters, and prolonged cool, dry periods, resulting in crop failure and poor livestock survival — and periods of famine. In the Great Famine of 1315–1317, most of Europe was affected and millions of people died, and further millions were left vulnerable to the Black Plague which ravaged Europe shortly after. That European populations are generally left out of such applications of the hypothesis is misguided.
This is not to suggest that “thrifty genes” don’t exist at all — but we likely need to go much further back in hominid evolution to see these. By now, such genetic variants are likely to be invariant and fixed in the modern human population. Rick Johnson and colleagues have proposed that the genetic inactivation of the enzyme uricase could be one such example.¹²
For Indigenous populations, we should also be considering the impact of colonialism — both the effects of population loss due to the introduction of western diseases to immunologically naïve populations (ie. populations who had never been exposed to these diseases before), and the effects of the structural inequalities that these populations have faced, with loss of traditional lands and lifeways.
Written by Anna Gosling and Tony Merriman.
- Neel, J. V. 1962. Diabetes mellitus: A “thrifty” genotype rendered detrimental by “progress”? Am J Hum Genet 14, 353–362.
- Gosling AL, Buckley HR, Matisoo-Smith E, Merriman TR. 2015. Pacific Populations, Metabolic Disease and ‘Just-So Stories’: A Critique of the ‘Thrifty Genotype’ Hypothesis in Oceania. Ann Hum Genet. Nov; 79(6):470–80.
- Wilmshurst, J. M., Hunt, T. L., Lipo, C. P. & Anderson, A. J. 2011. High-precision radiocarbon dating shows recent and rapid initial human colonization of East Polynesia. Proc Natl Acad Sci USA 108, 1815–1820.
- Sharp, A. 1956. Ancient voyagers in the Pacific. Wellington: Polynesian Society.
- Irwin, G. 1989. Against, across and down the wind: a case for the systematic exploration of the remote Pacific Islands. J Polyn Soc 98, 167–206.
- Kirch, P. 2000. On the road of the winds: An archaeological history of the Pacific Islands before European contact. Berkley: University of California Press.
- Fitzpatrick, S. M. 2007. Archaeology’s contribution to island studies. Isl Stud J 2, 77–100.
- Montenegro, A., Callaghan, R. T. & Fitzpatrick, S. M. 2014. From west to east: Environmental influences on the rate and pathways of Polynesian colonization. Holocene 24, 242–256.
- Houghton, P. 1990. The adaptive significance of Polynesian body form. Ann Hum Biol 17, 19–32.
- Hiroa, T. R. 1924. The evolution of Maori clothing. J Polyn Soc 33, 293–316.
- VanDijk, N. 1991. The Hansel and Gretel syndrome: A critique of Houghton’s cold adaptation hypothesis and an alternative model. NZJA 13, 65–89.
- Kratzer, J. T., Lanaspa, M. A., Murphy, M. N., Cicerchi, C., Graves, C. L., Tipton, P. A., Ortlund, E. A., Johnson, R. J. & Gaucher, E.A. 2014. Evolutionary history and metabolic insights of ancient mammalian uricases. Proc Natl Acad Sci USA 111, 3763–3768.
