30
2 The Genetic Context
Capacity of bony nasopharynx = (posterior nasal spine to basion distance) × chonal width
× (perpendicular from hormion to basion-posterior nasal spine line)/0.5
Using this formula we established a mean volume of 13.0 ml for the male Polynesian
nasopharynx, compared with 10.1 ml for Norwegians and 0.5 ml for Australian Aborigines.
That is, the Polynesian nasopharynx is on average about 30% larger than that of northern
European, and 35% larger than that of the Australian Aborigine (Kean and Houghton, 1972).
This is a substantial difference, and the influence on the voice of such a great resonating
chamber above the vocal cords (Sundaberg 1977; Proctor 1980) may contribute to the wellattested Polynesian singing abilities (pp. 108–109).
The extent and complexity of these changes are remarkable: the evolution of
the greater lung capacity and larger airway needed to supply oxygen to fuel larger
muscles led to a complex reshaping of the head, involving the development of a
larger cranial vault and large cranial capacity and so the evolution of the recognized
pentagonal shape of the Polynesian skull, while changes to the mandible led to the
evolution of the rocker jaw. With respect to the latter, Houghton comments that
The mature mandible represents the most extreme adaptation of the bone found amongst
Homo sapiens, and within Polynesia the Moriori with their exceptionally flat cranial bases
show the most extreme form of rocker jaw (p. 111).
Summarizing the results of his metabolic analysis, Houghton concludes [32]:
These figures for heat production and heat loss show that, in the oceanic environment
with only neolithic technology, a larger-bodied individual is at a quantifiable and crucial
advantage in maintaining body temperature. In addition, a thick muscular limb maintains
its warmth and function better. In these wet-cold oceanic conditions only an individual
approaching Polynesian proportions and muscularity could generally sustain body heat and
limb function. For individuals of lesser build the consequences would range from extreme
discomfort to hypothermia and death, depending on the persistence of the windy, wet-cold
conditions (p. 174).
We have quoted from Houghton’s analysis in detail because its implications for
the prehistory of the ancestors of the Lapita and Polynesian peoples are so striking.
Houghton notes that the evolution of a cold-adapted phenotype may have its roots in
a distant past: “The time that the selection for large body size took is uncertain, but
there is a big gap between the earliest date for human occupation of New Ireland,
33,000 BP (Allen et al. 1988) and the appearance of Lapita ware with its voyaging
associations about 3600 BP (Green 1982)” (p. 180).
Jim Bindon [33] has argued that recent research into thrifty genes has provided
some clues that the cold- and work-adapted body build and the metabolic shift to
accommodate dietary stress may be related:
These adaptations may be the result of mutations in the region of the insulin gene (INS),
like the variable number tandem repeat (VNTR) polymorphism near INS that modulates
transcription of both the INS gene and the nearby Insulin-like Growth Factor 2 (GF2)
gene. Increasing transcription of INS could generate high blood insulin levels (hyperinsulinemia) and decrease sensitivity to insulin binding in peripheral cells (insulin resistance).
Meanwhile, high levels of IGF2 stimulate muscular and skeletal growth predisposing to a
large, robust body.
2 The Genetic Context
Capacity of bony nasopharynx = (posterior nasal spine to basion distance) × chonal width
× (perpendicular from hormion to basion-posterior nasal spine line)/0.5
Using this formula we established a mean volume of 13.0 ml for the male Polynesian
nasopharynx, compared with 10.1 ml for Norwegians and 0.5 ml for Australian Aborigines.
That is, the Polynesian nasopharynx is on average about 30% larger than that of northern
European, and 35% larger than that of the Australian Aborigine (Kean and Houghton, 1972).
This is a substantial difference, and the influence on the voice of such a great resonating
chamber above the vocal cords (Sundaberg 1977; Proctor 1980) may contribute to the wellattested Polynesian singing abilities (pp. 108–109).
The extent and complexity of these changes are remarkable: the evolution of
the greater lung capacity and larger airway needed to supply oxygen to fuel larger
muscles led to a complex reshaping of the head, involving the development of a
larger cranial vault and large cranial capacity and so the evolution of the recognized
pentagonal shape of the Polynesian skull, while changes to the mandible led to the
evolution of the rocker jaw. With respect to the latter, Houghton comments that
The mature mandible represents the most extreme adaptation of the bone found amongst
Homo sapiens, and within Polynesia the Moriori with their exceptionally flat cranial bases
show the most extreme form of rocker jaw (p. 111).
Summarizing the results of his metabolic analysis, Houghton concludes [32]:
These figures for heat production and heat loss show that, in the oceanic environment
with only neolithic technology, a larger-bodied individual is at a quantifiable and crucial
advantage in maintaining body temperature. In addition, a thick muscular limb maintains
its warmth and function better. In these wet-cold oceanic conditions only an individual
approaching Polynesian proportions and muscularity could generally sustain body heat and
limb function. For individuals of lesser build the consequences would range from extreme
discomfort to hypothermia and death, depending on the persistence of the windy, wet-cold
conditions (p. 174).
We have quoted from Houghton’s analysis in detail because its implications for
the prehistory of the ancestors of the Lapita and Polynesian peoples are so striking.
Houghton notes that the evolution of a cold-adapted phenotype may have its roots in
a distant past: “The time that the selection for large body size took is uncertain, but
there is a big gap between the earliest date for human occupation of New Ireland,
33,000 BP (Allen et al. 1988) and the appearance of Lapita ware with its voyaging
associations about 3600 BP (Green 1982)” (p. 180).
Jim Bindon [33] has argued that recent research into thrifty genes has provided
some clues that the cold- and work-adapted body build and the metabolic shift to
accommodate dietary stress may be related:
These adaptations may be the result of mutations in the region of the insulin gene (INS),
like the variable number tandem repeat (VNTR) polymorphism near INS that modulates
transcription of both the INS gene and the nearby Insulin-like Growth Factor 2 (GF2)
gene. Increasing transcription of INS could generate high blood insulin levels (hyperinsulinemia) and decrease sensitivity to insulin binding in peripheral cells (insulin resistance).
Meanwhile, high levels of IGF2 stimulate muscular and skeletal growth predisposing to a
large, robust body.