20.11 Low Maori Genetic Diversity
367
significant contributions to the Maori gene pool by this stage, even though all these
early migrants would have intermarried with indigenous tribes for protection and
to obtain land rights. Nearly all of the genetic contribution to the gene pool at the
beginning of the Medieval Climatic Optimum would have been from the founding
first-wave Spice Island colonists.
We have noted that a power law estimate of a founder population of 289 is a
size in accord with the traditional practice of using fleets to found colonies. The
practice, mentioned from earliest times in oral records, clearly persisted down to the
Heke. The survival – physical, genetic and cultural – of a Lapita-age Spice Island
colony in New Zealand may well have depended on this practice of providing a
significant founder population, given both the long climate-imposed isolation of
the colony early in its history and the near-extinction event recorded in Moriori
tradition. Even though kin-based, a large founder population would have provided
greater initial genetic diversity, making survival of a near-extinction event more
likely and helping to counteract faster coalescence caused by extended early isolation which prevented the possibility of new genetic input for more than 600 years.
That the original Spice Island colony survived for 1,500 years, despite an early
extinction event and a long climate-enforced isolation, suggests that it was a large,
well-organized migration with a significant founder population (as archaeological
evidence shows most Lapita-age colonizations to have been).
The major loss of genetic diversity through an early near-extinction event might
alone account for most of the low genetic diversity of Maori. But this early loss
would have been compounded by the catastrophic population losses in New Zealand
during the Little Ice Age and from AD 1800 to AD 1896 following European
contact. The factors favouring higher genetic diversity in Eastern Polynesia and
the factors explaining limited genetic diversity in New Zealand are specific to
each region. Genetic outcomes for both can be seen as a consequence of the
relative time depths of settlement and of their own genetic and demographic
histories.
And yet, although a very considerable time depth in New Zealand would allow
for increased coalescence and so loss of genetic diversity, it would also allow for the
generation of genetic diversity through mutation. The four rare Maori haplotypes
discovered by Whyte, Marshall and Chambers [16], two of which are fast-evolving
and one of which is stated to have only a 33 generation mutation time, can be
explained as indigenous mutations, dispersed through coalescence into the genetic
matrix of New Zealand Maori. The contrast between Eastern Polynesian and Maori
haplotypes contradicts the claim that Eastern Polynesia was the sole source for
Maori genes. Of the 24 Eastern Polynesian haplotypes, New Zealand has only four
and of these only one is uniquely shared with Eastern Polynesia. Of the four held
in common three are also shared with Western Polynesia and two with Melanesia.
Four haplotypes out of nine appear to be indigenous, unique to Maori, unknown
elsewhere in Oceania. A long prehistory in New Zealand allows time for these haplotypes to represent indigenous mutations. Because migration was one way, from
Eastern Polynesia to New Zealand, these unique Maori mutations could not have
been shared with other parts of Polynesia.
367
significant contributions to the Maori gene pool by this stage, even though all these
early migrants would have intermarried with indigenous tribes for protection and
to obtain land rights. Nearly all of the genetic contribution to the gene pool at the
beginning of the Medieval Climatic Optimum would have been from the founding
first-wave Spice Island colonists.
We have noted that a power law estimate of a founder population of 289 is a
size in accord with the traditional practice of using fleets to found colonies. The
practice, mentioned from earliest times in oral records, clearly persisted down to the
Heke. The survival – physical, genetic and cultural – of a Lapita-age Spice Island
colony in New Zealand may well have depended on this practice of providing a
significant founder population, given both the long climate-imposed isolation of
the colony early in its history and the near-extinction event recorded in Moriori
tradition. Even though kin-based, a large founder population would have provided
greater initial genetic diversity, making survival of a near-extinction event more
likely and helping to counteract faster coalescence caused by extended early isolation which prevented the possibility of new genetic input for more than 600 years.
That the original Spice Island colony survived for 1,500 years, despite an early
extinction event and a long climate-enforced isolation, suggests that it was a large,
well-organized migration with a significant founder population (as archaeological
evidence shows most Lapita-age colonizations to have been).
The major loss of genetic diversity through an early near-extinction event might
alone account for most of the low genetic diversity of Maori. But this early loss
would have been compounded by the catastrophic population losses in New Zealand
during the Little Ice Age and from AD 1800 to AD 1896 following European
contact. The factors favouring higher genetic diversity in Eastern Polynesia and
the factors explaining limited genetic diversity in New Zealand are specific to
each region. Genetic outcomes for both can be seen as a consequence of the
relative time depths of settlement and of their own genetic and demographic
histories.
And yet, although a very considerable time depth in New Zealand would allow
for increased coalescence and so loss of genetic diversity, it would also allow for the
generation of genetic diversity through mutation. The four rare Maori haplotypes
discovered by Whyte, Marshall and Chambers [16], two of which are fast-evolving
and one of which is stated to have only a 33 generation mutation time, can be
explained as indigenous mutations, dispersed through coalescence into the genetic
matrix of New Zealand Maori. The contrast between Eastern Polynesian and Maori
haplotypes contradicts the claim that Eastern Polynesia was the sole source for
Maori genes. Of the 24 Eastern Polynesian haplotypes, New Zealand has only four
and of these only one is uniquely shared with Eastern Polynesia. Of the four held
in common three are also shared with Western Polynesia and two with Melanesia.
Four haplotypes out of nine appear to be indigenous, unique to Maori, unknown
elsewhere in Oceania. A long prehistory in New Zealand allows time for these haplotypes to represent indigenous mutations. Because migration was one way, from
Eastern Polynesia to New Zealand, these unique Maori mutations could not have
been shared with other parts of Polynesia.