THROUGH THE LENS OF ANTHROPOLOGY: AN INTRODUCTION TO HUMAN EVOLUTION AND CULTURE40

of years old. We really don’t know the variability within various species, genera, and other categories. A relatively small sample size also affects our ability to classify.

Understanding and describing primate evolution is simplified through the use of time periods called epochs, created by geologists. Epochs are based in part on observ-able changes in the geological record, including the record of plants and animals.

BOX 2.2 Rafting Monkeys

One of the most intriguing areas of interest in the study of primate evolution has to do with the origin of the Platyrrhini, commonly known as the New World monkeys. They begin to appear in the fossil record of Central and South America about 30 million years ago, but their antecedents are unknown.

One common hypothesis suggests there was ongoing evolution from some of the earliest forms of primates existing in North America during the Eocene. A problem is the lack of supporting evidence in the fossil record. While there were animals best described as primates in the region during the Oligocene, there is no evidence of primates at all in the fossil record for at least 10 million years before the Platyrrihini, and those early forms did not resemble monkeys.

Another hypothesis is that the earliest Platyrrhini rafted over from Africa. The rafts were presum-ably floating islands of natural debris. To some it seems like a far-fetched idea, but for many it seems the most probable scenario. This hypoth-esis is covered by Alan de Queiroz (2014) in his book The Monkey’s Voyage: How Improbable Journeys Shaped the History of Life. Several kinds of evidence are used in support of the hypothe-sis, including the knowledge that primates made it hundreds of miles from Africa to the island of Madagascar tens of millions of years ago (presumably by rafting on floating vegetation) and that, in more recent times, early populations of humans apparently traveled to some of the

islands of Southeast Asia. Other support includes the observation of very large natural rafts, includ-ing one described to be as large as Belgium and another with living trees growing to a height of 30 feet. Such natural rafts have been observed to occur at the mouths of rivers, where fallen trees and other kinds of vegetation accumulate and on occasion float into the ocean.

One of the biggest problems to deal with in accepting the hypothesis is the sheer size of the journey from Africa across the ocean to Central or South America. As pointed out by de Queiroz, while the distance today is about 1,800 miles, it was probably half that about 40 million years ago. It is also suggested that there were likely multiple islands in the ocean during the voyage.

Models factoring distance, currents, and winds suggest that the voyage could have been best measured in days rather than weeks. Further support is provided by the recognition of molec-ular studies suggesting that other animals also made the journey from Africa to the Americas via natural rafts, although these other animals were mostly lizards and snakes.

The fossil evidence may also be interpreted as supporting the rafting hypothesis. There are some primate fossils from the Oligocene in Africa that appear to be good candidates for being ancestral to both the Platyrrhini and Catarrhini, with evidence including, for example, the dental formula most commonly associated with Platyrrhini (2–1–3–3).

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