- Introduction
- Homo sapiens
- Approaches to understand modern human origin
(a) Complete replacement model
(b) Partial replacement model
(c) Regional continuity/multiregional model
(d) A critical appraisal of the models of modern human evolution - Major fossil discoveries of modern human
(i) Africa
(ii) Asia
(iii) Europe
(iv) Australia - Technology and art
(i) Upper Paleolithic technology
(ii) Upper Paleolithic arts
- Approaches to understand modern human origin
- Conclusions
- Summary points
Learning Objectives:
- To develop an understanding about characteristic features of H. sapiens.
- To describe various fossil finds discovered from several places in Africa, Asia, Europe and Australia.
- To discuss various models of the evolution of modern human.
- To describe Paleolithic and artistic cultural traditions associated with H. sapiens
INTRODUCTION
Over past few decades, scholars of several disciplines remained keen to understand emergence and evolution of biologically and behaviorally ‘modern’ human. New discoveries and new scientific techniques have changed the discourse about evolution of modern man. Sophisticated dating methods and molecular approaches have brought a paradigm shift in discoveries and interpretation on human evolution. Acknowledging abilities to exploit surrounding environment, emergence and existence of human particularly Homo sapiens remained central issue of debate in modern academic thoughts.
Discoveries of Homo erectus from several sites in different continents inculcated interest among
scholars to trace missing links between Homo erectus and Homo sapiens. Interpretation of Petralona skull by Stringer, Howell and Melentis showed that size of brain case, difference in skull structure pertaining to enlarged brain size are distinguishing features from Homo erectus to Homo sapiens (Stringer et al., 1979). Several discoveries from Africa, Europe, Asia, Australia and New world have established antiquity of Homo sapiens fossils and associated tool technologies as well as arts.
HOMO SAPIENS: There is no general agreement about the definition of Homo sapiens. Certain
biological and cultural characteristics are attributed to the species ‘sapiens’ which includes increased size of brain case, increased height of skull vault, smaller amount of constrictions or wasting behind the orbits, relatively lower position of ridges on skull for the attachment of neck muscles. Associated with this are cranial capacity of 900 to 2300 cc, rounded occiput, bent basicrania, maximum skull breadth higher on the skull, flatter face, well defined chin and smaller incisors as distinct feature of Homo sapiens. Postcranial features include straighter long bones with less articular surface for the attachment of muscles, bones are thinner than in Neanderthals, sockets of femurs are farther forwarded and less powerful grip, etc (Stein and Rowe, 2011).
Owing to changed climatic conditions during Pleistocene period Homo sapiens evolved and developed advance tool technology and associated art traditions. Upper Paleolithic period is mainly associated to early Homo sapiens. Several scholars believe that pictorial art originated with modern man. Although Neanderthal and modern people emerged almost together yet pictorial art developed not before 40,000 years ago. This suggests that pictorial art is a result of environmental changes and cultural exchange and not because of biological modifications. People before modern man might have other creative outlets which are a matter of investigation for present day palaeoanthropologists.
Approaches to Understanding Modern Human Origins
In attempting to organize and explain modern human origins, paleoanthropologists have proposed a few major theories that can be summarized into two contrasting views: the regional continuity model and various versions of replacement models. These two views are quite distinct, and in some ways they’re completely opposed to each other. Since so much of our contemporary view of modern human origins is influenced by the debates linked to these differing theories. Then we’ll turn to the fossil and archaeological evidence itself to see what it can contribute to answering the five questions we’ve posed.
a) The Regional Continuity Model: Multiregional Evolution
The regional continuity model is most closely associated with paleoanthropologist Milford Wolpoff, of the University of Michigan, and his associates (Wolpoff et al., 1994, 2001). They suggest that local populations—not all, of course—in Europe, Asia, and Africa continued their indigenous evolutionary development from premodern Middle Pleistocene forms to anatomically modern humans.
But if that’s true, then we have to ask how so many different local populations around the globe happened to evolve with such similar morphology. In other words, how could anatomically modern humans arise separately in different continents and end up so much alike, both physically and genetically? The multiregional model answers this question by (1) denying that the earliest modern H. sapiens populations originated exclusively in Africa and (2) asserting that significant levels of gene flow (migration) between various geographically dispersed premodern populations were extremely likely throughout the Pleistocene.
Through gene flow and natural selection, according to the multiregional hypothesis, local populations would not have evolved totally independently from one another, and such mixing would have “prevented speciation between the regional lineages and thus maintained human beings as a single, although obviously polytypic , species throughout the Pleistocene” (Smith et al., 1989). Thus, under a multiregional model, there are no taxonomic distinctions between modern and premodern hominins. That is, all hominins following H. erectus are classified as a single species: H. sapiens.
In light of emerging evidence over the last few years, almost all advocates of the multiregional model aren’t dogmatic about the degree of regional continuity. They recognize that a strong influence of modern humans evolving first in Africa has left an imprint on populations throughout the world that is still detectable today. Nevertheless, the most recent data suggest that multiregional models no longer tell us much about the origins of modern humans; nor do they seem to provide much information regarding the dispersal of modern H. sapiens.
b) Replacement Models
Replacement models all emphasize that modern humans first evolved in Africa and only later dispersed to other parts of the world, where they replaced those hominins already living in these other regions. In recent years, two versions of such replacement models have been proposed.
(i) The complete replacement model : proposes that anatomically modern populations arose in Africa within the last 200,000 years and then migrated from Africa, completely replacing populations in Europe and Asia (Stringer and Andrews, 1988). It’s important to note that this model doesn’t account for a transition from premodern forms to modern H. sapiens anywhere in the world except Africa. A critical deduction of the original Stringer and Andrews theory argued that anatomically modern humans appeared as the result of a biological speciation event. So in this view, migrating African modern H. sapiens could not have interbred with local non-African populations, because the African modern humans were a biologically different species. Taxonomically, all of the premodern populations outside Africa would, in this view, be classified as belonging to different species of Homo. For example, the Neandertals would be classified as H. neanderthalensis. This speciation explanation fits nicely with, and in fact helps explain, complete replacement; but Stringer has more recently stated that he isn’t insistent on this issue. He does suggest that even though there may have been potential for interbreeding, apparently very little actually took place.
Interpretations of the latter phases of human evolution have recently been greatly extended by newly available genetic techniques, and they’ve recently been applied to the question of modern human origins. Using numerous contemporary human populations as a data source, geneticists have precisely determined and compared a wide variety of DNA sequences. The theoretical basis of this approach assumes that at least some of the genetic patterning seen today can act as a kind of window into the past. In particular, the genetic patterns observed today between geographically widely dispersed humans are thought to partly reflect migrations occurring in the Late Pleistocene. This hypothesis can be further tested as contemporary population genetic patterning is better documented.
As these new data accumulate, consistent relationships are emerging, especially in showing that indigenous African populations have far greater diversity than do populations from elsewhere in the world. The consistency of the results is highly significant, because it strongly supports an African origin for modern humans and some mode of replacement elsewhere. New, even more complete data on contemporary population patterning for large portions of nuclear DNA further confirm these conclusions.
Certainly, most molecular data come from contemporary species, since DNA is not usually preserved in long-dead individuals. Even so, exceptions do occur, and these cases open another genetic window—one that can directly illuminate the past. mtDNA has been recovered from more than a dozen Neandertal fossils. In addition, researchers have recently sequenced the mtDNA of nine ancient fully modern H. sapiens skeletons from sites in Italy, France, the Czech Republic, and Russia (Caramelli et al., 2003, 2006; Kulikov et al., 2004; Serre et al., 2004). MtDNA data, however, are somewhat limited because mtDNA is a fairly small segment of DNA, and it is transmitted between generations as a single unit; genetically it acts like a single gene.
Indeed, in just the last few years, comparisons of Neandertal and early modern mtDNA led to some significant misinterpretations. Clearly, data from the vastly larger nuclear genome are far more informative. A giant leap forward occurred in 2010 when sequencing of the entire Neandertal nuclear genome was completed. Researchers immediately compared the Neandertal genome with that of people living today and discovered that some populations still retain some Neandertal genes (Green et al., 2010). Without doubt, we can now conclude that some interbreeding took place between Neandertals and modern humans, arguing against complete replacement and supporting some form of partial replacement.
(ii)Partial Replacement Models
For a number of years, several paleoanthropologists, including Günter Bräuer, of the University of Hamburg, suggested that very little interbreeding occurred— a view supported more recently by John Relethford (2001) in what he described as “mostly out of Africa.” The new findings from DNA analysis further confirm that the degree of interbreeding was modest, ranging from 1 to 4 percent in modern populations outside Africa; moreover, contemporary Africans have no trace of Neandertal genes, suggesting that any interbreeding occurred after modern humans migrated out of Africa. This would seem obvious when you consider that (as far as we know) Neandertals never lived anywhere in Africa. For our African ancestors to even have the opportunity to mate with a Neandertal, they would first have to leave their African homeland. Another fascinating discovery is that among the modern people so far sampled (five individuals), the three non-Africans all have some Neandertal DNA. The tentative conclusion from these preliminary findings suggests that the interbreeding occurred soon after modern humans emigrated out of Africa. The most likely scenario suggests that the intermixing occurred around 80,000–50,000 ya, quite possibly in the Middle East.
These results are very new and are partly based on very limited samples of living people. Technological innovations in DNA sequencing are occurring at an amazing pace, making it faster and cheaper. But it is still a challenge to sequence all the 3 billion+ nucleotides each of us has in our nuclear genome. When we have full genomes from more individuals living in many more geographical areas, the patterns of modern human dispersal should become clearer. Did the modern human-Neandertal interbreeding occur primarily in one area, or did it happen in several regions? And did some modern human populations several thousand years ago interbreed with their Neandertal cousins more than others did? Even more interesting, were there still other premodern human groups still around when modern humans emigrated from Africa— and did they interbreed, too?
From his study of fossil remains, Fred Smith, of Illinois State University, has proposed an “assimilation” model that hypothesizes that more interbreeding did take place, at least in some regions (Smith, 2002). To test these hypotheses and answer all the fascinating questions,
we will also need more whole-genome DNA from ancient remains, particularly from early modern human skeletons. This, too, won’t be an easy task; remember, it took four years of intensive effort to decode and reassemble the Neandertal genome. Then, too, we need to be aware that DNA thousands of years old can be obtained from hominin remains that are found in environments that have been persistently cold (or at least cool). In tropical areas, DNA degrades rapidly; so it seems a long shot that any usable DNA can be obtained from hominins that lived in many extremely large and significant regions (for example, Africa and Southeast Asia)