AGE OF MAN. - The problem of the age of the h. r. remains one of the most difficult and controversial, since its solution is bound up with that of other problems of a geological, geophysical and astronomical nature that are still the subject of lively discussion. Among these one may mention: the boundary between the Pliocene and the Pleistocene; the synchronization of the Neozoic deposits of the various continents and the interpretation of the famous "eoliths" found in various levels of the Cenozoic. These will be rapidly reviewed.
The appearance and spread of man are certainly among the most important phenomena characterizing the Neozoic or Quaternary era, so much so that it is also called the Anthropozoic. But it is not clear whether the appearance of man coincides with the beginning of the era or precedes or follows it.
In order to give a complete clarification on this point, one would first of all have to establish the precise epoch of the beginning of the Pleistocene, that is, of the first period of the Neozoic era. But on this authors are by no means in agreement. Some hold that the beginning of the Pleistocene is marked by the migration into Europe of certain important groups of Asiatic mammals, such as elephants and bovids. But it is objected that the European fauna of that time (Villafranchian) still displays markedly Pliocene characters and is therefore still to be considered Cenozoic. Others, more appropriately, make the beginning of the Quaternary coincide with that of the great glacial expansions, which cloaked vast zones of the boreal hemisphere and all the principal mountain chains with mighty ice sheets. This grandiose phenomenon is attested, besides by morainic and fluvioglacial formations, also by migrations of continental and marine Arctic faunas into the European and Mediterranean regions. The preference here is for this last version. But even granting this, it still remains to be established at what moment, relative to the glacial period, the first appearance of man occurred, that is, whether it preceded the glaciations, or corresponded to one of the periods of glacial expansion, or again to one of the warm periods interposed between them, called interglacials, and, among these, to which one precisely. But here matters become terribly complicated, because it is not yet known how many glaciations there were, whose number, according to different authors, varies from two to as many as twelve.
At present the majority of specialists propose three or at most four glaciations, called respectively Günz, Mindel, Riss and Würm, after the names of four Alpine watercourses. But since the first glacial (Günz) is not accepted by everyone, it happens that sometimes the same deposits are attributed, depending on the author, to the preglacial (Villafranchian) or to the first interglacial (Günz-Mindel).
The solution of the problem is rendered even more difficult by the fact that it is not simple to synchronize the deposits of different regions, especially those of regions in which glacial invasions did or did not occur, for example, the European deposits with those of the Far East or of tropical Africa. But apart from this, even within Europe itself it is evident that the evidence of climatic changes appears in the deposits of the northern regions somewhat earlier than in the coeval formations of the southern regions, especially the Mediterranean ones.
Bearing in mind what has been set out thus far, an attempt will now be made to see what the oldest evidence so far known of the existence of man is, and to what epochs it can be traced back. In Europe the oldest human being so far known is represented by the Mauer mandible (palaeanthropus heidelbergensis) found in western Germany, which according to the most reliable authors would be referable to the first interglacial. Roughly contemporary would be the Sinanthropus (sinanthropus pekinensis) of China and, according to some, some individual of the famous Pithecanthropi of Java (pithecanthropus erectus, p. robustus). All these most ancient representatives of humanity display markedly pithecoid characters. Until recently the majority of authors considered roughly contemporary with these also the Eoanthropus (eoanthropus dawsoni) of Piltdown, in England, but recent research conducted with the "fluorine method" has cast serious doubt on its such high antiquity.
To the same interglacial are referred the first certain evidence of human industry, consisting of very coarse but certainly intentional lithic artifacts, referable to the Abbevillian (= Chellean) and Clactonian cultures, and in traces of fire. According to some authors, however, there would be remains of human industry also in older, preglacial formations. As for the famous and much debated "eoliths" found even in Miocene and Eocene deposits, no one any longer gives them credence, but on the other hand the presence of true artifacts in some English preglacial "crags", and in some Villafranchian deposit of Europe or Africa, cannot be excluded. Very recent is the report (Arambourg, 1949) in the Villafranchian of Algeria of curious polyhedral flints, to which it is difficult to deny the character of artifacts. One cannot therefore exclude at least the possibility that man appeared already at the end of the Pliocene, before the beginning of the great glacial expansions.
On the whole, then, it may be considered probable that the appearance of man corresponds roughly to the period of transition between the Pliocene and the Pleistocene. This conclusion agrees well also with current knowledge (still rather scanty, to tell the truth) about the primates from which the human body could have derived by evolution. Indeed it is precisely at the end of the Pliocene and the beginning of the Pleistocene that there appear on the one hand the anthropomorphic apes closest to human characters (australopithecines) and on the other the most primitive hominids mentioned above (Mauer, Sinanthropus, Pithecanthropi).
This being established, it remains to be seen whether it is possible to determine how many years ago the appearance of man dates back. Here too one is far from having a secure basis, since absolute chronology is still in its infancy. There are at present various methods for dating the principal events of the Neozoic era. The first, more reliable, is based on the study of the so-called "varves", that is, of particular stratified clays that were deposited in the great lakes near the sources of the Neozoic ice during the last period of retreat. Since it is known that each pair of layers of these clays corresponds to one year, one can calculate the duration of the retreat period of the last glaciation, which has been estimated at about 18,000 years by De Geer and his pupils for Scandinavia. This method, however, is valid only for postglacial times, corresponding, as is known, only to the most recent periods of prehistory (from the Mesolithic onward).
For earlier periods one resorts to a second method, which is less reliable, being still based on theoretical conceptions whose application to Quaternary climatic phenomena is not entirely demonstrated, but which is now accepted, albeit with some reservation, by a good part of Quaternary specialists. This is the method based on the so-called "Milankovitch curve", that is, on the curve of variations in solar radiation, calculated by the author cited on the basis of the periodic variations of certain elements of the Earth's orbit, precisely of the following: eccentricity of the orbit, obliquity of the ecliptic and heliocentric longitude of the perihelion. The variation in the quantity of solar radiation, dependent on the variations of the above-mentioned elements, and on which in turn depend, according to Milankovitch, the climatic alternations of the glacial period, has been calculated exactly for the last 600,000 years and with a certain approximation for another 400,000 years before that.
Now from these calculations it would appear that the 1st glaciation (that of Günz, since Milankovitch admits 4 glaciations) would have begun ca. 600,000 years ago, and that if Man appeared — as the more reliable authors think — at least during the first interglacial (Günz-Mindel), his existence would go back to ca. 300,000 years.
It is well, however, to bear in mind the hypothetical character that these evaluations still present, which in any case can give us only the order of magnitude of the periods with which we are dealing.
At present the possibility is being studied of applying also to the chronology of the Neozoic era the methods based on radioactivity, that is, on the computation of the time corresponding to the disintegration of certain isotopes of radioactive minerals, among which mention will be made of thorium 220 for research on deep-sea sediments and carbon 14 for substances containing that isotope, which sometimes accompany prehistoric human remains. The latter research relating to carbon is valid, however, only for limited durations and, in general, the methods based on radioactivity are still in their initial phase and for now offer only relative guarantees.
In any case, it may be considered by now accepted, on the basis of a whole complex of factual data and well-founded considerations, that human prehistory corresponds to an extremely long period of time, and that the appearance of man therefore goes back to an epoch much more ancient than was believed until some time ago.
BIBL.: sources