THE ROLE OF DATING IN HUMAN EVOLUTION STUDIES
Significance of the temporal framework of human origins has been felt always. As a number of new discoveries of hominid remains and occupation sites came to light in the years since WWII, fresh fossil data and contextual information started pouring in. Without an accurate chronological background, it is as such impossible to locate the fossils in space and time, to examine local lineages for signs of supposed evolutionary trends, to document the geographic spread of any species and the coexistence of distinct types of hominid, or actual replacement of one population by another, and many such details. Accurate age data of the fossils as well as of the sites played an important role in piecing together the records.
In this regard, the role of dating to determine the age of fossils and archaeological artefacts in the human evolution studies is enormous. During most of the last century, age attributes of European fossil hominids have generally been decided by associated archaeological association (if any), or on the basis of their associated fauna and/or flora in the context of the succession of recognized continental glacial and interglacial stages and sub-stages (Stringer et al. 1984).
As observed by Grun and Stringer (1991), before 1970 it was believed by many researchers that Europe or the Middle East were centres of origin of modern humans. Some considered that a form of Neanderthal or 'Neanderthaloid' population was the most likely precursor of modern humans. Moreover, sub-Saharan Africa and the Far East were generally considered as insignificant or retarded backwaters in recent human evolution. Such views were partly a reflection of the better (or better-known) fossil and archaeological materials from Europe and western Asia (Grun and Stringer, 1991) prevailing at that time.
Lack of adequate age data on late Pleistocene hominid sequence had created an artificial clustering of fossils with morphologically comparable hominids, or similar archaeology or associated faunas/floras. This had led to a probable compression of the actual chronology for many of the sites into the period between 30 and 50 ka (Grun and stringer, 1991); this became apparent with the application of new techniques. Dating techniques based on uranium series, thermoluminescence, and electron spin resonance made their greatest impact as they stretched a condensed chronology to a more realistic length. Some examples are discussed below.
Conventional radiocarbon method was earlier being used for determining almost all Aterian-related chronologies (Aterian - Middle Paleolithic stone tool industry of North Africa). As we know, radiocarbon dating method is reliable only for ages younger than 40–50 ka. In addition to technical limitations of the dating method, there have been conceptual preconceptions in dating the Aterian, as it was originally thought to be associated with a humid episode which was presumably dated to 40–20 ka ago. Consequently, all dates older than 40 ka, being infinite, were getting discarded.
These assumptions can now be rejected for several reasons. In order to obtain more reliable dates than infinite ones, other dating methods have been used and compared with the radiocarbon method. Thus, in 2009, Barton and Abdeljalil Bouzouggar of the National Institute of Archaeological and Heritage Sciences in Rabat reported optically-stimulated luminescence dates of at least 110,000 years from the Aterian site of Dar es-Soltane in Morocco (Balter, 2011, p. 23).
The importance of accurate dating and creation of an absolute timescale to the resolution of various issues concerning human evolution is obvious.
For example, based on the primate fossil record, scientists know that living primates evolved from fossil primates and that this evolutionary history took tens of millions of years. By comparing fossils of different primate species, scientists can examine how features changed and how primates evolved through time. However, the age of each fossil primate needs to be determined so that fossils of the same age found in different parts of the world and fossils of different ages can be compared (Peppe and Deino, 2013).
Another example, volcanic minerals from associated strata in the Olduvai Gorge were dated to approximately 1.75 ma using the K–Ar method. This greatly expanded the time range for regarding the australopithecines as human ancestors rather than extinct collateral cousins to the “true” human lineage, as considered earlier (Gundling, 2010).
Likewise, Duller ( 2001) has discussed the contributions of geochronology in resolving two main issues of peopling of Asia and Australia. One - the timing of arrival of Homo erectus in Southeast Asia, and subsequently the arrival of Homo sapiens. Another issue is the timing of the arrival of hominids in the Australian continental area (Sahul).
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