Glenda Lewis
Last week we explained how some of the DNA we inherit from our mothers enables us to trace the journeys of our ancestors out of Africa. This clever reverse tracking, comparing the DNA from living people and fossils, was the brainchild of New Zealand scientist Allan Wilson.
To recap: everyone inherits a small loop of DNA from their mother, which is not combined with father’s DNA when the sperm fertilises the egg. It sits outside the cell nucleus where all our other DNA resides. This DNA is contained in, and is the work-plan for, our mitochondria, which are self-contained spherical units that generate the energy to drive cell functions.
Occasionally, on average once every 100 generations, there is a mutation in this mitochondrial DNA (mtDNA). Once a mutation occurs, it is passed on to all future generations of that woman’s children and thus acts as an ancestral sign post. These changes enable evolutionary biologists to trace our maternal line very accurately, going right back to our common origins in Africa.
Maternal lineages, characterised by these mutations, are labelled by alternating letters and numbers. All non-Africans descend from one maternal lineage (L3) that left Africa about 65,000 years ago. Each time a mutation that is shared by a large number of people is identified, the branch on the human family tree splits and is given a number. So the B branch may split into four branches – B1, B2, B3 and B4.
Then when those branches split, the new lineages, or subbranches, are given letters, so B4 splits into B4a and B4b and so on. The next level splits are numbered – B4a1, B4a2 etc, then B4a1a, B4a1a1, B4a1a1. These specific subbranches, with their letter and number designations, are called haplogroups, and are like a postcode designation of where your mtDNA sits on the growing human family tree.
Most Polynesians, including Ma¯ori, have mtDNA that belongs to the B4a1a branches. No Ma¯orispecific mtDNA lineages have been identified, as all of the lineages identified in Ma¯ori are also found in other Polynesian populations, which is to be expected given the timing and history of settlement.
The mutations that define the B branch of the mtDNA family tree first occurred between 40,000 and 50,000 years ago in Asia. About a third of indigenous Americans are also of the B lineage, but are on the B2 branch. Their ancestors migrated from Asia to America before the land bridge disappeared at the end of the last Ice Age, about 10,000 years ago. People carrying the B4a1a lineages spread down through island Southeast Asia and eastward into the Pacific.
These early island dwellers are known as the Lapita people, identified by remains of their pottery which has distinctive patterns of indentation. Lapita sites first appear around the Bismarck Archipelago (New Guinea) about 3350 years ago, and the Lapita were the first people to settle Vanuatu, New Caledonia, Fiji, Tonga and Samoa, about 3000 years ago.
It was another 2000 years before the next big push into Central and East Polynesia, journeys of several thousand kilometres. These bold voyagers sailed east against the prevailing winds which means that these journeys were probably deliberate explorations and not random excursions. That they found tiny, vastly separated places
DNA evidence shows the founding population of Aotearoa must have numbered in the hundreds,
reports in the second and final article on human migration to this land.
such as Hawaii and Easter Island is a testament to their sailing and navigational skills.
Even Captain Cook was impressed, and he knew what was involved. ‘‘How shall we account for this nation spreading itself over so vast an ocean?’’ he wondered. Cook noted how very similar all the island languages were – an indication of very recent separation.
Language evolution is a proxy for human DNA changes and migration. Tupaia, the highranking priest Cook took with him in 1769 when he left Tahiti, was able to communicate with Ma¯ori in Uawa/Tolaga Bay on the East Coast. They may never have been allowed onshore otherwise. Our islands were the last to be discovered – the end of a 65,000-year diaspora by humans, who used their creative ingenuity to adapt to any habitat, from Siberia to the American deserts.
In excavations undertaken from the 1930s through the 1960s,