3.4 HUMANS ACROSS THE EARTH

If people have a common origin, then why do some groups of people look so strikingly different from others? Has environment shaped the appearance of people, or are the differences just a matter of chance? Finally, if humans indeed came 'out of Africa', how did that happen and when? In this article, we will examine these questions, review briefly what is known, and finally--discuss some of the ways that answers are sought.

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I. PHYSICAL DIFFERENCE AND ENVIRONMENT

Human populations in different parts of the world have adjusted to the physical environment in different ways. Some bodily differences are immediately noticeable, such as skin color, nose shape, body form, hair, and eye color. Remarkably, little is known of the adaptive significance of these physical differences. Obvious traits include skin color, nose shape, hair color, eye color. Are variations in these traits advantageous in some environments?

Surprisingly, little is known of the adaptive significance of these traits. In the Old World, light colored skin may favor vitamin D production. A narrow nose may better moisten and warm air in bitterly cold environments. Eskimo tend to be short limbed, a significant benefit in minimizing heat loss.

Implicit in these questions is the idea that people have always been where they were found during the age of European expansion. The history of people on Earth, however, is one of movement. For example, when explorers examined the south Pacific, they found islands occupied by people who looked alike and often spoke similar languages. How did they get there?

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II. BUILD A RAFT AND TRAVEL THERE

The Norwegian Thor Hyerdahl built a raft with balsa wood logs lashed together and made headlines with a bold experiment: he set out by sea westward from Peru to demonstrate that Polynesian peoples could have come from South America. His book, Kon-Tiki sold 20 million copies, easily more than all (other) books in anthropology....combined! Hyerdahl's adventure fascinated millions--including this writer.

Kon Tiki was an experiment based on this premise: if he could sail from Peru to Polynesia on a primitive raft, the ancients could have done it. Researchers have looked at the problem of Polynesian origins using another premise: when people move, they take their biology, material culture, and language with them.

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Genetic analysis became possible with the discovery of blood groups. The ABO system was first described in 1900; many others are now known. The distribution of them across the world is strongly patterned. For example, blood groups A and B occur with high frequency in Africa and much of Asia. In contrast, A and B are almost entirely absent amongst aboriginal populations except for west central North America where A is common. The ABO pattern may reflect natural selection and random genetic drift; however, it offers a tantalizing first clue to people origins.

When genes for blood groups, enzymes, MtDNA and nuclear DNA are mapped in the Pacific region, large scale patterns appear. There is a genetic link between the modern populations of Southeast Asia and the small islands of Polynesia. One other pattern is interesting: the populations of the more distant islands are rather uniform, suggesting small founder populations and population bottlenecks in their history.

(My note: MtDNA hit anthropology big time when the first MtDNA study in humans was announced and the popular press christened it as the "Eve Hypothesis." Is it valid? Studies of MtDNA in mice and fruit flies give misleading clues about historical relatedness of populations.Yet, much of the evidence is intriguing.)

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When people move, they take their languages with them. We learn languages effortlessly as children, but only with difficulty as adults. Thus, they tend to be retained when people move.

When expanding agricultural populations spread out from China they carried their genes, culture, and language into much of eastern Asia and the Pacific. Areas as far flung as Polynesia (by 200 BC), Hawaii (200 AD), and New Zealand (800 AD) have a common linguistic heritage. The word for 'eye' (mata) is about the same in the Philippines, Fiji, Samoa, and even that enigmatic far-flung outpost--Easter Island.

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Many of the Pacific Islands appear to have been populated for less than 5,000 years, many much more recently. Easter Island seems to have been settled in 400 AD, went through a population boom and crash, and has suffered massive ecological damage from overexploitation of the island.

The encroachment of humans into new habitats extinguished many plants and animals throughout Polynesia. The most unfortunate loss probably was the loss of the giant birds of New Zealand.

When the refugees of the Mutiny of the Bounty explored Pitcairn and nearby Henderson Island, they made a chilling discovery that of earlier peoples had lived there--and went extinct.

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Kon Tiki survives as a remarkable adventure, but as science, it has been sunk. Polynesians didn't come from South America.

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III. WALKING TO AMERICA

When Europeans came to the Americas 500 years ago, a native Indian connection to Asia occurred to them. Columbus, using an incorrect diameter of the Earth in his navigating assumed he had reached Asia. Some thought them to be the lost tribes of Israel. The Jesuit de Acosta suggested that New World peoples came from Asia. Later knowledge of the Ice Ages provided a mechanism: when sea levels lowered during glaciation, a land bridge opened between Asia and America. Ice Age hunters following large game came to inhabit the New World 12,000 years ago.

The theory is accepted, but the timing of the earliest invasion is debated. A unique piece of material culture, a fluted stone spear tip--the Clovis point--is found widely in the Americas and part of Asia and no where else. It seemed to have been used for about 500 years nearly twelve millenia ago.

Monte Verde in Chile and the Monte Alegre site in Brazil have won increasing support as evidences of an even earlier entry into the Americas.

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The populating of the Americas by peoples from Asia is supported by three lines of evidence: sinodont dental traits (that include shovel-shaped incisors), genetic studies (specifically Gm allotypes), and language studies. Those first Americans according to the model came in three successive migrations. The earliest immigrants were Paleoindians at the close of the Ice Ages. Two subsequent migrations were the Athabascans and the Aleut-Eskimo.

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IV. CONCLUDING REMARKS

In this brief article we have briefly reviewed theories and evidence for the peopling of Polynesia and the New World. These two 'models' have been chosen to illustrate the creative use of linguistic, cultural, and genetic evidence in establishing the origins of people.

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..... CJ '98

Resources:

Bunney, S. ed. Cambridge Encyclopedia of Human Evolution. New York: Cambridge University Press, 1994.

Fagan, B. Ancient North America. New York: Thames and Hudson Inc., 1995